skia2/site/user/api/SkMatrix_Reference.md

SkMatrix Reference

Matrix

Class SkMatrix

Matrix holds a 3x3 matrix for transforming coordinates. This allows mapping Points and Vectors with translation, scaling, skewing, rotation, and perspective.

Matrix elements are in row major order. Matrix does not have a constructor, so it must be explicitly initialized. setIdentity initializes Matrix so it has no effect. setTranslate, setScale, setSkew, setRotate, set9 and setAll initializes all Matrix elements with the corresponding mapping.

Matrix includes a hidden variable that classifies the type of matrix to improve performance. Matrix is not thread safe unless getType is called first.

Overview

Subtopics

topics	description

Operators

function	description
operator!=(const SkMatrix& a, const SkMatrix& b)	Returns true if members are unequal.
operator==(const SkMatrix& a, const SkMatrix& b)	Returns true if members are equal.
operator[](int index) const	Returns Matrix value.
operator[](int index)	Returns writable reference to Matrix value.

Member Functions

function	description
Concat	Returns the concatenation of Matrix pair.
I	Returns a reference to a const identity Matrix.
InvalidMatrix	Returns a reference to a const invalid Matrix.
MakeAll	Constructs all nine values.
MakeRectToRect	Constructs from source Rect to destination Rect.
MakeScale	Constructs from scale in x and y.
MakeTrans	Constructs from translate in x and y.
SetAffineIdentity	Sets 3x2 array to identity.
asAffine	Copies to 3x2 array.
cheapEqualTo	Compares Matrix pair using memcmp().
decomposeScale	Separates scale if possible.
dirtyMatrixTypeCache	Sets internal cache to unknown state.
dump	Sends text representation using floats to standard output.
fixedStepInX	Returns step in x for a position in y.
get	Returns one of nine Matrix values.
get9	Returns all nine Matrix values.
getMaxScale	Returns maximum scaling, if possible.
getMinMaxScales	Returns minimum and maximum scaling, if possible.
getMinScale	Returns minimum scaling, if possible.
getPerspX	Returns input x perspective factor.
getPerspY	Returns input y perspective factor.
getScaleX	Returns horizontal scale factor.
getScaleY	Returns vertical scale factor.
getSkewX	Returns horizontal skew factor.
getSkewY	Returns vertical skew factor.
getTranslateX	Returns horizontal translation.
getTranslateY	Returns vertical translation.
getType	Returns transform complexity.
hasPerspective	Returns if transform includes perspective.
invert	Returns inverse, if possible.
isFinite	Returns if all Matrix values are not infinity, NaN.
isFixedStepInX	Returns if transformation supports fixed step in x.
isIdentity	Returns if matrix equals the identity Matrix .
isScaleTranslate	Returns if transform is limited to scale and translate.
isSimilarity	Returns if transform is limited to square scale and rotation.
isTranslate	Returns if transform is limited to translate.
mapHomogeneousPoints	Maps Point3 array.
mapPoints	Maps Point array.
mapRadius	Returns mean radius of mapped Circle.
mapRect	Returns bounds of mapped Rect.
mapRectScaleTranslate	Returns bounds of mapped Rect.
mapRectToQuad	Maps Rect to Point array.
mapVector	Maps Vector.
mapVectors	Maps Vector array.
mapXY	Maps Point.
postConcat	Post-multiplies Matrix by Matrix parameter.
postIDiv	Post-multiplies Matrix by inverse scale.
postRotate	Post-multiplies Matrix by rotation.
postScale	Post-multiplies Matrix by scale.
postSkew	Post-multiplies Matrix by skew.
postTranslate	Post-multiplies Matrix by translation.
preConcat	Pre-multiplies Matrix by Matrix parameter.
preRotate	Pre-multiplies Matrix by rotation.
preScale	Pre-multiplies Matrix by scale.
preSkew	Pre-multiplies Matrix by skew.
preTranslate	Pre-multiplies Matrix by translation.
preservesAxisAlignment	Returns if mapping restricts to 90 degree multiples and mirroring.
preservesRightAngles	Returns if mapped 90 angle remains 90 degrees.
rectStaysRect	Returns if mapped Rect can be represented by another Rect.
reset	Sets Matrix to identity.
set	Sets one value.
set9	Sets all values from Scalar array.
setAffine	Sets left two columns.
setAll	Sets all values from parameters.
setConcat	Sets to Matrix parameter multiplied by Matrix parameter.
setIdentity	Sets Matrix to identity.
setPerspX	Sets input x perspective factor.
setPerspY	Sets input y perspective factor.
setPolyToPoly	Sets to map one to four points to an equal array of points.
setRSXform	Sets to rotate, scale, and translate.
setRectToRect	Sets to map one Rect to another.
setRotate	Sets to rotate about a point.
setScale	Sets to scale about a point.
setScaleTranslate	Sets to scale and translate.
setScaleX	Sets horizontal scale factor.
setScaleY	Sets vertical scale factor
setSinCos	Sets to rotate and scale about a point.
setSkew	Sets to skew about a point.
setSkewX	Sets horizontal skew factor.
setSkewY	Sets vertical skew factor.
setTranslate	Sets to translate in x and y.
setTranslateX	Sets horizontal translation.
setTranslateY	Sets vertical translation.
toString	Converts Matrix to machine readable form.

MakeScale

static SkMatrix SK_WARN_UNUSED_RESULT MakeScale(SkScalar sx, SkScalar sy)

Sets Matrix to scale by (sx, sy). Returned matrix is:

| sx  0  0 |
|  0 sy  0 |
|  0  0  1 |

Parameters

sx	horizontal scale factor
sy	vertical scale factor

Return Value

Matrix with scale

Example

See Also

setScale postScale preScale

---

static SkMatrix SK_WARN_UNUSED_RESULT MakeScale(SkScalar scale)

Sets Matrix to scale by (scale, scale). Returned matrix is:

| scale   0   0 |
|   0   scale 0 |
|   0     0   1 |

Parameters

scale

horizontal and vertical scale factor

Return Value

Matrix with scale

Example

See Also

setScale postScale preScale

---

MakeTrans

static SkMatrix SK_WARN_UNUSED_RESULT MakeTrans(SkScalar dx, SkScalar dy)

Sets Matrix to translate by (dx, dy). Returned matrix is:

| 1 0 dx |
| 0 1 dy |
| 0 0  1 |

Parameters

dx	horizontal translation
dy	vertical translation

Return Value

Matrix with translation

Example

See Also

setTranslate postTranslate preTranslate

---

MakeAll

static SkMatrix SK_WARN_UNUSED_RESULT MakeAll(SkScalar scaleX, SkScalar skewX, SkScalar transX,
                                              SkScalar skewY, SkScalar scaleY, SkScalar transY,
                                              SkScalar pers0, SkScalar pers1, SkScalar pers2)

Sets Matrix to:

| scaleX  skewX transX |
|  skewY scaleY transY |
|  pers0  pers1  pers2 |

Parameters

scaleX	horizontal scale factor
skewX	horizontal skew factor
transX	horizontal translation
skewY	vertical skew factor
scaleY	vertical scale factor
transY	vertical translation
pers0	input x perspective factor
pers1	input y perspective factor
pers2	perspective scale factor

Return Value

Matrix constructed from parameters

Example

See Also

setAll set9 postConcat preConcat

---

Enum SkMatrix::TypeMask

enum TypeMask {
kIdentity Mask = 0,
kTranslate Mask = 0x01,
kScale Mask = 0x02,
kAffine Mask = 0x04,
kPerspective Mask = 0x08,
};

Enum of bit fields for mask returned by getType. Used to identify the complexity of Matrix, to optimize performance.

Constants

SkMatrix::kIdentity_Mask	0	all bits clear if Matrix is identity
SkMatrix::kTranslate_Mask	1	set if Matrix has translation
SkMatrix::kScale_Mask	2	set if Matrix has x or y scale
SkMatrix::kAffine_Mask	4	set if Matrix skews or rotates
SkMatrix::kPerspective_Mask	8	set if Matrix has perspective

Example

Example Output

after reset: kIdentity_Mask
after postTranslate: kTranslate_Mask
after postScale: kTranslate_Mask kScale_Mask
after postScale: kTranslate_Mask kScale_Mask kAffine_Mask
after setPolyToPoly: kTranslate_Mask kScale_Mask kAffine_Mask kPerspective_Mask

See Also

getType

getType

TypeMask getType() const

Returns a bit field describing the transformations the matrix may perform. The bit field is computed conservatively, so it may include false positives. For example, when kPerspective Mask is set, all other bits are set.

Return Value

kIdentity Mask, or combinations of: kTranslate Mask, kScale Mask, kAffine Mask, kPerspective Mask

Example

Example Output

identity flags hex: 0 decimal: 0
set all  flags hex: f decimal: 15

See Also

TypeMask

---

isIdentity

bool isIdentity() const

Returns true if Matrix is identity. Identity matrix is:

| 1 0 0 |
| 0 1 0 |
| 0 0 1 |

Return Value

true if Matrix has no effect

Example

Example Output

is identity: true
is identity: false

See Also

reset setIdentity getType

---

isScaleTranslate

bool isScaleTranslate() const

Returns true if Matrix at most scales and translates. Matrix may be identity, contain only scale elements, only translate elements, or both. Matrix form is:

| scale-x    0    translate-x |
|    0    scale-y translate-y |
|    0       0         1      |

Return Value

true if Matrix is identity; or scales, translates, or both

Example

Example Output

is scale-translate: true
is scale-translate: true
is scale-translate: true
is scale-translate: true

See Also

setScale isTranslate setTranslate getType

---

isTranslate

bool isTranslate() const

Returns true if Matrix is identity, or translates. Matrix form is:

| 1 0 translate-x |
| 0 1 translate-y |
| 0 0      1      |

Return Value

true if Matrix is identity, or translates

Example

Example Output

is translate: true
is translate: true
is translate: false
is translate: false

See Also

setTranslate getType

---

rectStaysRect

bool rectStaysRect() const

Returns true Matrix maps Rect to another Rect. If true, Matrix is identity, or scales, or rotates a multiple of 90 degrees, or mirrors in x or y. In all cases, Matrix may also have translation. Matrix form is either:

| scale-x    0    translate-x |
|    0    scale-y translate-y |
|    0       0         1      |

or

|    0     rotate-x translate-x |
| rotate-y    0     translate-y |
|    0        0          1      |

for non-zero values of scale-x, scale-y, rotate-x, and rotate-y.

Also called preservesAxisAlignment; use the one that provides better inline documentation.

Return Value

true if Matrix maps one Rect into another

Example

Example Output

rectStaysRect: true
rectStaysRect: true
rectStaysRect: true
rectStaysRect: true

See Also

preservesAxisAlignment preservesRightAngles

---

preservesAxisAlignment

bool preservesAxisAlignment() const

Returns true Matrix maps Rect to another Rect. If true, Matrix is identity, or scales, or rotates a multiple of 90 degrees, or mirrors in x or y. In all cases, Matrix may also have translation. Matrix form is either:

| scale-x    0    translate-x |
|    0    scale-y translate-y |
|    0       0         1      |

or

|    0     rotate-x translate-x |
| rotate-y    0     translate-y |
|    0        0          1      |

for non-zero values of scale-x, scale-y, rotate-x, and rotate-y.

Also called rectStaysRect; use the one that provides better inline documentation.

Return Value

true if Matrix maps one Rect into another

Example

Example Output

preservesAxisAlignment: true
preservesAxisAlignment: true
preservesAxisAlignment: true
preservesAxisAlignment: true

See Also

rectStaysRect preservesRightAngles

---

hasPerspective

bool hasPerspective() const

Returns true if the matrix contains perspective elements. Matrix form is:

|       --            --              --          |
|       --            --              --          |
| perspective-x  perspective-y  perspective-scale |

where perspective-x or perspective-y is non-zero, or perspective-scale is not one. All other elements may have any value.

Return Value

true if Matrix is in most general form

Example

See Also

setAll set9 MakeAll

---

isSimilarity

bool isSimilarity(SkScalar tol = SK_ScalarNearlyZero) const

Returns true if Matrix contains only translation, rotation, reflection, and uniform scale. Returns false if Matrix contains different scales, skewing, perspective, or degenerate forms that collapse to a line or point.

Describes that the Matrix makes rendering with and without the matrix are visually alike; a transformed circle remains a circle. Mathematically, this is referred to as similarity of a Euclidean_Space, or a similarity transformation.

Preserves right angles, keeping the arms of the angle equal lengths.

Parameters

tol	to be deprecated

Return Value

true if Matrix only rotates, uniformly scales, translates

Example

String is drawn four times through but only two are visible. Drawing the pair with isSimilarity false reveals the pair not visible through the matrix.

See Also

isScaleTranslate preservesRightAngles rectStaysRect isFixedStepInX

---

preservesRightAngles

bool preservesRightAngles(SkScalar tol = SK_ScalarNearlyZero) const

Returns true if Matrix contains only translation, rotation, reflection, and scale. Scale may differ along rotated axes. Returns false if Matrix skewing, perspective, or degenerate forms that collapse to a line or point.

Preserves right angles, but not requiring that the arms of the angle retain equal lengths.

Parameters

tol	to be deprecated

Return Value

true if Matrix only rotates, scales, translates

Example

Equal scale is both similar and preserves right angles. Unequal scale is not similar but preserves right angles. Skews are not similar and do not preserve right angles.

See Also

isScaleTranslate isSimilarity rectStaysRect isFixedStepInX

---

Enum SkMatrix::_anonymous

enum {
kMScaleX,
kMSkewX,
kMTransX,
kMSkewY,
kMScaleY,
kMTransY,
kMPersp0,
kMPersp1,
kMPersp2,
};

Matrix organizes its values in row order. These members correspond to each value in Matrix.

Constants

SkMatrix::kMScaleX	0	horizontal scale factor
SkMatrix::kMSkewX	1	horizontal skew factor
SkMatrix::kMTransX	2	horizontal translation
SkMatrix::kMSkewY	3	vertical skew factor
SkMatrix::kMScaleY	4	vertical scale factor
SkMatrix::kMTransY	5	vertical translation
SkMatrix::kMPersp0	6	input x perspective factor
SkMatrix::kMPersp1	7	input y perspective factor
SkMatrix::kMPersp2	8	perspective bias

Example

See Also

get set

Enum SkMatrix::_anonymous_2

enum {
kAScaleX,
kASkewY,
kASkewX,
kAScaleY,
kATransX,
kATransY,
};

Affine arrays are in column major order to match the matrix used by PDF and XPS.

Constants

SkMatrix::kAScaleX	0	horizontal scale factor
SkMatrix::kASkewY	1	vertical skew factor
SkMatrix::kASkewX	2	horizontal skew factor
SkMatrix::kAScaleY	3	vertical scale factor
SkMatrix::kATransX	4	horizontal translation
SkMatrix::kATransY	5	vertical translation

See Also

SetAffineIdentity asAffine setAffine

operator[]

SkScalar operator[](int index) _const

Returns one matrix value. Asserts if index is out of range and SK_DEBUG is defined.

Parameters

index

one of: kMScaleX, kMSkewX, kMTransX, kMSkewY, kMScaleY, kMTransY, kMPersp0, kMPersp1, kMPersp2

Return Value

value corresponding to index

Example

Example Output

matrix[SkMatrix::kMScaleX] == 42
matrix[SkMatrix::kMScaleY] == 24

See Also

get set

---

get

SkScalar get(int index) const

Returns one matrix value. Asserts if index is out of range and SK_DEBUG is defined.

Parameters

index

one of: kMScaleX, kMSkewX, kMTransX, kMSkewY, kMScaleY, kMTransY, kMPersp0, kMPersp1, kMPersp2

Return Value

value corresponding to index

Example

Example Output

matrix.get(SkMatrix::kMSkewX) == 42
matrix.get(SkMatrix::kMSkewY) == 24

See Also

operator[](int index) set

---

getScaleX

SkScalar getScaleX() const

Returns scale factor multiplied by x input, contributing to x output. With mapPoints, scales Points along the x-axis.

Return Value

horizontal scale factor

Example

Example Output

matrix.getScaleX() == 42

See Also

get getScaleY setScaleX setScale

---

getScaleY

SkScalar getScaleY() const

Returns scale factor multiplied by y input, contributing to y output. With mapPoints, scales Points along the y-axis.

Return Value

vertical scale factor

Example

Example Output

matrix.getScaleY() == 24

See Also

get getScaleX setScaleY setScale

---

getSkewY

SkScalar getSkewY() const

Returns scale factor multiplied by x input, contributing to y output. With mapPoints, skews Points along the y-axis. Skew x and y together can rotate Points.

Return Value

vertical skew factor

Example

Example Output

matrix.getSkewY() == 24

See Also

get getSkewX setSkewY setSkew

---

getSkewX

SkScalar getSkewX() const

Returns scale factor multiplied by y input, contributing to x output. With mapPoints, skews Points along the x-axis. Skew x and y together can rotate Points.

Return Value

horizontal scale factor

Example

Example Output

matrix.getSkewX() == 42

See Also

get getSkewY setSkewX setSkew

---

getTranslateX

SkScalar getTranslateX() const

Returns translation contributing to x output. With mapPoints, moves Points along the x-axis.

Return Value

horizontal translation factor

Example

Example Output

matrix.getTranslateX() == 42

See Also

get getTranslateY setTranslateX setTranslate

---

getTranslateY

SkScalar getTranslateY() const

Returns translation contributing to y output. With mapPoints, moves Points along the y-axis.

Return Value

vertical translation factor

Example

Example Output

matrix.getTranslateY() == 24

See Also

get getTranslateX setTranslateY setTranslate

---

getPerspX

SkScalar getPerspX() const

Returns factor scaling input x relative to input y.

Return Value

input x perspective factor

Example

See Also

kMPersp0 getPerspY

---

getPerspY

SkScalar getPerspY() const

Returns factor scaling input y relative to input x.

Return Value

input y perspective factor

Example

See Also

kMPersp1 getPerspX

---

operator[]

SkScalar& operator[](int index)

Returns writable Matrix value. Asserts if index is out of range and SK_DEBUG is defined. Clears internal cache anticipating that caller will change Matrix value.

Next call to read Matrix state may recompute cache; subsequent writes to Matrix value must be followed by dirtyMatrixTypeCache.

Parameters

index

one of: kMScaleX, kMSkewX, kMTransX, kMSkewY, kMScaleY, kMTransY, kMPersp0, kMPersp1, kMPersp2

Return Value

writable value corresponding to index

Example

Example Output

with identity matrix: x = 24
after skew x mod:     x = 24
after 2nd skew x mod: x = 24
after dirty cache:    x = 66

See Also

get dirtyMatrixTypeCache set

---

set

void set(int index, SkScalar value)

Sets Matrix value. Asserts if index is out of range and SK_DEBUG is defined. Safer than operator[]; internal cache is always maintained.

Parameters

index	one of: kMScaleX, kMSkewX, kMTransX, kMSkewY, kMScaleY, kMTransY, kMPersp0, kMPersp1, kMPersp2
value	Scalar to store in Matrix

Example

Example Output

with identity matrix: x = 24
after skew x mod:     x = 24
after 2nd skew x mod: x = 66

See Also

operator[] get

---

setScaleX

void setScaleX(SkScalar v)

Sets horizontal scale factor.

Parameters

v	horizontal scale factor to store

Example

See Also

set setScale setScaleY

---

setScaleY

void setScaleY(SkScalar v)

Sets vertical scale factor.

Parameters

v	vertical scale factor to store

Example

See Also

set setScale setScaleX

---

setSkewY

void setSkewY(SkScalar v)

Sets vertical skew factor.

Parameters

v	vertical skew factor to store

Example

See Also

set setSkew setSkewX

---

setSkewX

void setSkewX(SkScalar v)

Sets horizontal skew factor.

Parameters

v	horizontal skew factor to store

Example

See Also

set setSkew setSkewX

---

setTranslateX

void setTranslateX(SkScalar v)

Sets horizontal translation.

Parameters

v	horizontal translation to store

Example

See Also

set setTranslate setTranslateY

---

setTranslateY

void setTranslateY(SkScalar v)

Sets vertical translation.

Parameters

v	vertical translation to store

Example

See Also

set setTranslate setTranslateX

---

setPerspX

void setPerspX(SkScalar v)

Sets input x perspective factor, which causes mapXY to vary input x inversely proportional to input y.

Parameters

v	perspective factor

Example

See Also

getPerspX set setAll set9 MakeAll

---

setPerspY

void setPerspY(SkScalar v)

Sets input y perspective factor, which causes mapXY to vary input y inversely proportional to input x.

Parameters

v	perspective factor

Example

See Also

getPerspY set setAll set9 MakeAll

---

setAll

void setAll(SkScalar scaleX, SkScalar skewX, SkScalar transX, SkScalar skewY, SkScalar scaleY,
            SkScalar transY, SkScalar persp0, SkScalar persp1, SkScalar persp2)

Sets all values from parameters. Sets matrix to:

| scaleX  skewX transX |
|  skewY scaleY transY |
| persp0 persp1 persp2 |

Parameters

scaleX	horizontal scale factor to store
skewX	horizontal skew factor to store
transX	horizontal translation to store
skewY	vertical skew factor to store
scaleY	vertical scale factor to store
transY	vertical translation to store
persp0	input x perspective factor to store
persp1	input y perspective factor to store
persp2	perspective scale factor to store

Example

See Also

set9 MakeAll

---

get9

void get9(SkScalar buffer[9]) const

Copies nine Scalar values contained by Matrix into buffer, in member value ascending order: kMScaleX, kMSkewX, kMTransX, kMSkewY, kMScaleY, kMTransY, kMPersp0, kMPersp1, kMPersp2.

Parameters

buffer

storage for nine Scalar values

Example

Example Output

{4, 0, 3},
{0, 5, 4},
{0, 0, 1}

See Also

set9

---

set9

void set9(const SkScalar buffer[9])

Sets Matrix to nine Scalar values in buffer, in member value ascending order: kMScaleX, kMSkewX, kMTransX, kMSkewY, kMScaleY, kMTransY, kMPersp0, kMPersp1, kMPersp2.

Sets matrix to:

| buffer[0] buffer[1] buffer[2] |
| buffer[3] buffer[4] buffer[5] |
| buffer[6] buffer[7] buffer[8] |

In the future, set9 followed by get9 may not return the same values. Since Matrix maps non-homogeneous coordinates, scaling all nine values produces an equivalent transformation, possibly improving precision.

Parameters

buffer

nine Scalar values

Example

See Also

setAll get9 MakeAll

---

reset

void reset()

Sets Matrix to identity; which has no effect on mapped Points. Sets Matrix to:

| 1 0 0 |
| 0 1 0 |
| 0 0 1 |

Also called setIdentity; use the one that provides better inline documentation.

Example

Example Output

m.isIdentity(): true

See Also

isIdentity setIdentity

---

setIdentity

void setIdentity()

Sets Matrix to identity; which has no effect on mapped Points. Sets Matrix to:

| 1 0 0 |
| 0 1 0 |
| 0 0 1 |

Also called reset; use the one that provides better inline documentation.

Example

Example Output

m.isIdentity(): true

See Also

isIdentity reset

---

setTranslate

void setTranslate(SkScalar dx, SkScalar dy)

Sets Matrix to translate by (dx, dy).

Parameters

dx	horizontal translation
dy	vertical translation

Example

See Also

setTranslateX setTranslateY

---

void setTranslate(const SkVector& v)

Sets Matrix to translate by (v.fX, v.fY).

Parameters

v	Vector containing horizontal and vertical translation

Example

See Also

setTranslateX setTranslateY MakeTrans

---

setScale

void setScale(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py)

Sets Matrix to scale by sx and sy, about a pivot point at (px, py). The pivot point is unchanged when mapped with Matrix.

Parameters

sx	horizontal scale factor
sy	vertical scale factor
px	pivot x
py	pivot y

Example

See Also

setScaleX setScaleY MakeScale preScale postScale

---

void setScale(SkScalar sx, SkScalar sy)

Sets Matrix to scale by sx and sy about at pivot point at (0, 0).

Parameters

sx	horizontal scale factor
sy	vertical scale factor

Example

See Also

setScaleX setScaleY MakeScale preScale postScale

---

setRotate

void setRotate(SkScalar degrees, SkScalar px, SkScalar py)

Sets Matrix to rotate by degrees about a pivot point at (px, py). The pivot point is unchanged when mapped with Matrix.

Positive degrees rotates clockwise.

Parameters

degrees	angle of axes relative to upright axes
px	pivot x
py	pivot y

Example

See Also

setSinCos preRotate postRotate

---

void setRotate(SkScalar degrees)

Sets Matrix to rotate by degrees about a pivot point at (0, 0). Positive degrees rotates clockwise.

Parameters

degrees

angle of axes relative to upright axes

Example

See Also

setSinCos preRotate postRotate

---

setSinCos

void setSinCos(SkScalar sinValue, SkScalar cosValue, SkScalar px, SkScalar py)

Sets Matrix to rotate by sinValue and cosValue, about a pivot point at (px, py). The pivot point is unchanged when mapped with Matrix.

Vector (sinValue, cosValue) describes the angle of rotation relative to (0, 1). Vector length specifies scale.

Parameters

sinValue	rotation vector x component
cosValue	rotation vector y component
px	pivot x
py	pivot y

Example

See Also

setRotate setScale setRSXform

---

void setSinCos(SkScalar sinValue, SkScalar cosValue)

Sets Matrix to rotate by sinValue and cosValue, about a pivot point at (0, 0).

Vector (sinValue, cosValue) describes the angle of rotation relative to (0, 1). Vector length specifies scale.

Parameters

sinValue	rotation vector x component
cosValue	rotation vector y component

Example

Canvas needs offset after applying Matrix to pivot about Rect center.

See Also

setRotate setScale setRSXform

---

setRSXform

SkMatrix& setRSXform(const SkRSXform& rsxForm)

Sets Matrix to rotate, scale, and translate using a compressed matrix form.

Vector (rsxForm.fSSin, rsxForm.fSCos) describes the angle of rotation relative to (0, 1). Vector length specifies scale. Mapped point is rotated and scaled by Vector, then translated by (rsxForm.fTx, rsxForm.fTy).

Parameters

rsxForm

compressed RSXform matrix

Return Value

reference to Matrix

Example

Canvas needs offset after applying Matrix to pivot about Rect center.

See Also

setSinCos setScale setTranslate

---

setSkew

void setSkew(SkScalar kx, SkScalar ky, SkScalar px, SkScalar py)

Sets Matrix to skew by kx and ky, about a pivot point at (px, py). The pivot point is unchanged when mapped with Matrix.

Parameters

kx	horizontal skew factor
ky	vertical skew factor
px	pivot x
py	pivot y

Example

See Also

setSkewX setSkewY preSkew postSkew

---

void setSkew(SkScalar kx, SkScalar ky)

Sets Matrix to skew by kx and ky, about a pivot point at (0, 0).

Parameters

kx	horizontal skew factor
ky	vertical skew factor

Example

See Also

setSkewX setSkewY preSkew postSkew

---

setConcat

void setConcat(const SkMatrix& a, const SkMatrix& b)

Sets Matrix to Matrix a multiplied by Matrix b. Either a or b may be this.

Given:

    | A B C |      | J K L |
a = | D E F |, b = | M N O |
    | G H I |      | P Q R |

sets Matrix to:

        | A B C |   | J K L |   | AJ+BM+CP AK+BN+CQ AL+BO+CR |
a * b = | D E F | * | M N O | = | DJ+EM+FP DK+EN+FQ DL+EO+FR |
        | G H I |   | P Q R |   | GJ+HM+IP GK+HN+IQ GL+HO+IR |

Parameters

a	Matrix on left side of multiply expression
b	Matrix on right side of multiply expression

Example

setPolyToPoly creates perspective matrices, one the inverse of the other. Multiplying the matrix by its inverse turns into an identity matrix.

See Also

Concat preConcat postConcat SkCanvas::concat

---

preTranslate

void preTranslate(SkScalar dx, SkScalar dy)

Sets Matrix to Matrix multiplied by Matrix constructed from translation (dx, dy). This can be thought of as moving the point to be mapped before applying Matrix.

Given:

         | A B C |               | 1 0 dx |
Matrix = | D E F |,  T(dx, dy) = | 0 1 dy |
         | G H I |               | 0 0  1 |

sets Matrix to:

                     | A B C | | 1 0 dx |   | A B A*dx+B*dy+C |
Matrix * T(dx, dy) = | D E F | | 0 1 dy | = | D E D*dx+E*dy+F |
                     | G H I | | 0 0  1 |   | G H G*dx+H*dy+I |

Parameters

dx	x translation before applying Matrix
dy	y translation before applying Matrix

Example

See Also

postTranslate setTranslate MakeTrans

---

preScale

void preScale(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py)

Sets Matrix to Matrix multiplied by Matrix constructed from scaling by (sx, sy) about pivot point (px, py). This can be thought of as scaling about a pivot point before applying Matrix.

Given:

         | A B C |                       | sx  0 dx |
Matrix = | D E F |,  S(sx, sy, px, py) = |  0 sy dy |
         | G H I |                       |  0  0  1 |

where

dx = px - sx * px
dy = py - sy * py

sets Matrix to:

                             | A B C | | sx  0 dx |   | A*sx B*sy A*dx+B*dy+C |
Matrix * S(sx, sy, px, py) = | D E F | |  0 sy dy | = | D*sx E*sy D*dx+E*dy+F |
                             | G H I | |  0  0  1 |   | G*sx H*sy G*dx+H*dy+I |

Parameters

sx	horizontal scale factor
sy	vertical scale factor
px	pivot x
py	pivot y

Example

See Also

postScale setScale MakeScale

---

void preScale(SkScalar sx, SkScalar sy)

Sets Matrix to Matrix multiplied by Matrix constructed from scaling by (sx, sy) about pivot point (0, 0). This can be thought of as scaling about the origin before applying Matrix.

Given:

         | A B C |               | sx  0  0 |
Matrix = | D E F |,  S(sx, sy) = |  0 sy  0 |
         | G H I |               |  0  0  1 |

sets Matrix to:

                     | A B C | | sx  0  0 |   | A*sx B*sy C |
Matrix * S(sx, sy) = | D E F | |  0 sy  0 | = | D*sx E*sy F |
                     | G H I | |  0  0  1 |   | G*sx H*sy I |

Parameters

sx	horizontal scale factor
sy	vertical scale factor

Example

See Also

postScale setScale MakeScale

---

preRotate

void preRotate(SkScalar degrees, SkScalar px, SkScalar py)

Sets Matrix to Matrix multiplied by Matrix constructed from rotating by degrees about pivot point (px, py). This can be thought of as rotating about a pivot point before applying Matrix.

Positive degrees rotates clockwise.

Given:

         | A B C |                        | c -s dx |
Matrix = | D E F |,  R(degrees, px, py) = | s  c dy |
         | G H I |                        | 0  0  1 |

where

c  = cos(degrees)
s  = sin(degrees)
dx =  s * py + (1 - c) * px
dy = -s * px + (1 - c) * py

sets Matrix to:

                              | A B C | | c -s dx |   | Ac+Bs -As+Bc A*dx+B*dy+C |
Matrix * R(degrees, px, py) = | D E F | | s  c dy | = | Dc+Es -Ds+Ec D*dx+E*dy+F |
                              | G H I | | 0  0  1 |   | Gc+Hs -Gs+Hc G*dx+H*dy+I |

Parameters

degrees	angle of axes relative to upright axes
px	pivot x
py	pivot y

Example

See Also

postRotate setRotate

---

void preRotate(SkScalar degrees)

Sets Matrix to Matrix multiplied by Matrix constructed from rotating by degrees about pivot point (0, 0). This can be thought of as rotating about the origin before applying Matrix.

Positive degrees rotates clockwise.

Given:

         | A B C |                        | c -s 0 |
Matrix = | D E F |,  R(degrees, px, py) = | s  c 0 |
         | G H I |                        | 0  0 1 |

where

c  = cos(degrees)
s  = sin(degrees)

sets Matrix to:

                              | A B C | | c -s 0 |   | Ac+Bs -As+Bc C |
Matrix * R(degrees, px, py) = | D E F | | s  c 0 | = | Dc+Es -Ds+Ec F |
                              | G H I | | 0  0 1 |   | Gc+Hs -Gs+Hc I |

Parameters

degrees

angle of axes relative to upright axes

Example

See Also

postRotate setRotate

---

preSkew

void preSkew(SkScalar kx, SkScalar ky, SkScalar px, SkScalar py)

Sets Matrix to Matrix multiplied by Matrix constructed from skewing by (kx, ky) about pivot point (px, py). This can be thought of as skewing about a pivot point before applying Matrix.

Given:

         | A B C |                       |  1 kx dx |
Matrix = | D E F |,  K(kx, ky, px, py) = | ky  1 dy |
         | G H I |                       |  0  0  1 |

where

dx = -kx * py
dy = -ky * px

sets Matrix to:

                             | A B C | |  1 kx dx |   | A+B*ky A*kx+B A*dx+B*dy+C |
Matrix * K(kx, ky, px, py) = | D E F | | ky  1 dy | = | D+E*ky D*kx+E D*dx+E*dy+F |
                             | G H I | |  0  0  1 |   | G+H*ky G*kx+H G*dx+H*dy+I |

Parameters

kx	horizontal skew factor
ky	vertical skew factor
px	pivot x
py	pivot y

Example

See Also

postSkew setSkew

---

void preSkew(SkScalar kx, SkScalar ky)

Sets Matrix to Matrix multiplied by Matrix constructed from skewing by (kx, ky) about pivot point (0, 0). This can be thought of as skewing about the origin before applying Matrix.

Given:

         | A B C |               |  1 kx 0 |
Matrix = | D E F |,  K(kx, ky) = | ky  1 0 |
         | G H I |               |  0  0 1 |

sets Matrix to:

                     | A B C | |  1 kx 0 |   | A+B*ky A*kx+B C |
Matrix * K(kx, ky) = | D E F | | ky  1 0 | = | D+E*ky D*kx+E F |
                     | G H I | |  0  0 1 |   | G+H*ky G*kx+H I |

Parameters

kx	horizontal skew factor
ky	vertical skew factor

Example

See Also

postSkew setSkew

---

preConcat

void preConcat(const SkMatrix& other)

Sets Matrix to Matrix multiplied by Matrix other. This can be thought of mapping by other before applying Matrix.

Given:

         | A B C |          | J K L |
Matrix = | D E F |, other = | M N O |
         | G H I |          | P Q R |

sets Matrix to:

                 | A B C |   | J K L |   | AJ+BM+CP AK+BN+CQ AL+BO+CR |
Matrix * other = | D E F | * | M N O | = | DJ+EM+FP DK+EN+FQ DL+EO+FR |
                 | G H I |   | P Q R |   | GJ+HM+IP GK+HN+IQ GL+HO+IR |

Parameters

other

Matrix on right side of multiply expression

Example

setPolyToPoly creates perspective matrices, one the inverse of the other. Multiplying the matrix by its inverse turns into an identity matrix.

See Also

postConcat setConcat Concat

---

postTranslate

void postTranslate(SkScalar dx, SkScalar dy)

Sets Matrix to Matrix constructed from translation (dx, dy) multiplied by Matrix. This can be thought of as moving the point to be mapped after applying Matrix.

Given:

         | J K L |               | 1 0 dx |
Matrix = | M N O |,  T(dx, dy) = | 0 1 dy |
         | P Q R |               | 0 0  1 |

sets Matrix to:

                     | 1 0 dx | | J K L |   | J+dx*P K+dx*Q L+dx*R |
T(dx, dy) * Matrix = | 0 1 dy | | M N O | = | M+dy*P N+dy*Q O+dy*R |
                     | 0 0  1 | | P Q R |   |      P      Q      R |

Parameters

dx	x translation after applying Matrix
dy	y translation after applying Matrix

Example

Compare with preTranslate example.

See Also

preTranslate setTranslate MakeTrans

---

postScale

void postScale(SkScalar sx, SkScalar sy, SkScalar px, SkScalar py)

Sets Matrix to Matrix constructed from scaling by (sx, sy) about pivot point (px, py), multiplied by Matrix. This can be thought of as scaling about a pivot point after applying Matrix.

Given:

         | J K L |                       | sx  0 dx |
Matrix = | M N O |,  S(sx, sy, px, py) = |  0 sy dy |
         | P Q R |                       |  0  0  1 |

where

dx = px - sx * px
dy = py - sy * py

sets Matrix to:

                             | sx  0 dx | | J K L |   | sx*J+dx*P sx*K+dx*Q sx*L+dx+R |
S(sx, sy, px, py) * Matrix = |  0 sy dy | | M N O | = | sy*M+dy*P sy*N+dy*Q sy*O+dy*R |
                             |  0  0  1 | | P Q R |   |         P         Q         R |

Parameters

sx	horizontal scale factor
sy	vertical scale factor
px	pivot x
py	pivot y

Example

See Also

preScale setScale MakeScale

---

void postScale(SkScalar sx, SkScalar sy)

Sets Matrix to Matrix constructed from scaling by (sx, sy) about pivot point (0, 0), multiplied by Matrix. This can be thought of as scaling about the origin after applying Matrix.

Given:

         | J K L |               | sx  0  0 |
Matrix = | M N O |,  S(sx, sy) = |  0 sy  0 |
         | P Q R |               |  0  0  1 |

sets Matrix to:

                     | sx  0  0 | | J K L |   | sx*J sx*K sx*L |
S(sx, sy) * Matrix = |  0 sy  0 | | M N O | = | sy*M sy*N sy*O |
                     |  0  0  1 | | P Q R |   |    P    Q    R |

Parameters

sx	horizontal scale factor
sy	vertical scale factor

Example

See Also

preScale setScale MakeScale

---

postIDiv

bool postIDiv(int divx, int divy)

Sets Matrix to Matrix constructed from scaling by(1/divx, 1/divy)about pivot point (px, py), multiplied by Matrix.

Returns false if either divx or divy is zero.

Given:

         | J K L |                   | sx  0  0 |
Matrix = | M N O |,  I(divx, divy) = |  0 sy  0 |
         | P Q R |                   |  0  0  1 |

where

sx = 1 / divx
sy = 1 / divy

sets Matrix to:

                         | sx  0  0 | | J K L |   | sx*J sx*K sx*L |
I(divx, divy) * Matrix = |  0 sy  0 | | M N O | = | sy*M sy*N sy*O |
                         |  0  0  1 | | P Q R |   |    P    Q    R |

Parameters

divx	integer divisor for inverse scale in x
divy	integer divisor for inverse scale in y

Return Value

true on successful scale

Example

See Also

postScale MakeScale

---

postRotate

void postRotate(SkScalar degrees, SkScalar px, SkScalar py)

Sets Matrix to Matrix constructed from rotating by degrees about pivot point (px, py), multiplied by Matrix. This can be thought of as rotating about a pivot point after applying Matrix.

Positive degrees rotates clockwise.

Given:

         | J K L |                        | c -s dx |
Matrix = | M N O |,  R(degrees, px, py) = | s  c dy |
         | P Q R |                        | 0  0  1 |

where

c  = cos(degrees)
s  = sin(degrees)
dx =  s * py + (1 - c) * px
dy = -s * px + (1 - c) * py

sets Matrix to:

                              |c -s dx| |J K L|   |cJ-sM+dx*P cK-sN+dx*Q cL-sO+dx+R|
R(degrees, px, py) * Matrix = |s  c dy| |M N O| = |sJ+cM+dy*P sK+cN+dy*Q sL+cO+dy*R|
                              |0  0  1| |P Q R|   |         P          Q          R|

Parameters

degrees	angle of axes relative to upright axes
px	pivot x
py	pivot y

Example

See Also

preRotate setRotate

---

void postRotate(SkScalar degrees)

Sets Matrix to Matrix constructed from rotating by degrees about pivot point (0, 0), multiplied by Matrix. This can be thought of as rotating about the origin after applying Matrix.

Positive degrees rotates clockwise.

Given:

         | J K L |                        | c -s 0 |
Matrix = | M N O |,  R(degrees, px, py) = | s  c 0 |
         | P Q R |                        | 0  0 1 |

where

c  = cos(degrees)
s  = sin(degrees)

sets Matrix to:

                              | c -s dx | | J K L |   | cJ-sM cK-sN cL-sO |
R(degrees, px, py) * Matrix = | s  c dy | | M N O | = | sJ+cM sK+cN sL+cO |
                              | 0  0  1 | | P Q R |   |     P     Q     R |

Parameters

degrees

angle of axes relative to upright axes

Example

See Also

preRotate setRotate

---

postSkew

void postSkew(SkScalar kx, SkScalar ky, SkScalar px, SkScalar py)

Sets Matrix to Matrix constructed from skewing by (kx, ky) about pivot point (px, py), multiplied by Matrix. This can be thought of as skewing about a pivot point after applying Matrix.

Given:

         | J K L |                       |  1 kx dx |
Matrix = | M N O |,  K(kx, ky, px, py) = | ky  1 dy |
         | P Q R |                       |  0  0  1 |

where

dx = -kx * py
dy = -ky * px

sets Matrix to:

                             | 1 kx dx| |J K L|   |J+kx*M+dx*P K+kx*N+dx*Q L+kx*O+dx+R|
K(kx, ky, px, py) * Matrix = |ky  1 dy| |M N O| = |ky*J+M+dy*P ky*K+N+dy*Q ky*L+O+dy*R|
                             | 0  0  1| |P Q R|   |          P           Q           R|

Parameters

kx	horizontal skew factor
ky	vertical skew factor
px	pivot x
py	pivot y

Example

See Also

preSkew setSkew

---

void postSkew(SkScalar kx, SkScalar ky)

Sets Matrix to Matrix constructed from skewing by (kx, ky) about pivot point (0, 0), multiplied by Matrix. This can be thought of as skewing about the origin after applying Matrix.

Given:

         | J K L |               |  1 kx 0 |
Matrix = | M N O |,  K(kx, ky) = | ky  1 0 |
         | P Q R |               |  0  0 1 |

sets Matrix to:

                     |  1 kx 0 | | J K L |   | J+kx*M K+kx*N L+kx*O |
K(kx, ky) * Matrix = | ky  1 0 | | M N O | = | ky*J+M ky*K+N ky*L+O |
                     |  0  0 1 | | P Q R |   |      P      Q      R |

Parameters

kx	horizontal skew factor
ky	vertical skew factor

Example

See Also

preSkew setSkew

---

postConcat

void postConcat(const SkMatrix& other)

Sets Matrix to Matrix other multiplied by Matrix. This can be thought of mapping by other after applying Matrix.

Given:

         | J K L |           | A B C |
Matrix = | M N O |,  other = | D E F |
         | P Q R |           | G H I |

sets Matrix to:

                 | A B C |   | J K L |   | AJ+BM+CP AK+BN+CQ AL+BO+CR |
other * Matrix = | D E F | * | M N O | = | DJ+EM+FP DK+EN+FQ DL+EO+FR |
                 | G H I |   | P Q R |   | GJ+HM+IP GK+HN+IQ GL+HO+IR |

Parameters

other

Matrix on left side of multiply expression

Example

See Also

preConcat setConcat Concat

---

Enum SkMatrix::ScaleToFit

enum ScaleToFit {
kFill ScaleToFit,
kStart ScaleToFit,
kCenter ScaleToFit,
kEnd ScaleToFit,
};

ScaleToFit describes how Matrix is constructed to map one Rect to another. ScaleToFit may allow Matrix to have unequal horizontal and vertical scaling, or may restrict Matrix to square scaling. If restricted, ScaleToFit specifies how Matrix maps to the side or center of the destination Rect.

Constants

SkMatrix::kFill_ScaleToFit	0	Computes Matrix that scales in x and y independently, so that source Rect is mapped to completely fill destination Rect. The aspect ratio of source Rect may change.
SkMatrix::kStart_ScaleToFit	1	Computes Matrix that maintains source Rect aspect ratio, mapping source Rect width or height to destination Rect. Aligns mapping to left and top edges of destination Rect.
SkMatrix::kCenter_ScaleToFit	2	Computes Matrix that maintains source Rect aspect ratio, mapping source Rect width or height to destination Rect. Aligns mapping to center of destination Rect.
SkMatrix::kEnd_ScaleToFit	3	Computes Matrix that maintains source Rect aspect ratio, mapping source Rect width or height to destination Rect. Aligns mapping to right and bottom edges of destination Rect.

Example

See Also

setRectToRect MakeRectToRect setPolyToPoly

setRectToRect

bool setRectToRect(const SkRect& src, const SkRect& dst, ScaleToFit stf)

Sets Matrix to scale and translate src Rect to dst Rect. stf selects whether mapping completely fills dst or preserves the aspect ratio, and how to align src within dst. Returns false if src is empty, and sets Matrix to identity. Returns true if dst is empty, and sets Matrix to:

| 0 0 0 |
| 0 0 0 |
| 0 0 1 |

Parameters

src	Rect to map from
dst	Rect to map to
stf	one of: kFill ScaleToFit, kStart ScaleToFit, kCenter ScaleToFit, kEnd ScaleToFit

Return Value

true if Matrix can represent Rect mapping

Example

Example Output

src: 0, 0, 0, 0  dst: 0, 0, 0, 0  success: false
[  1.0000   0.0000   0.0000][  0.0000   1.0000   0.0000][  0.0000   0.0000   1.0000]
src: 0, 0, 0, 0  dst: 5, 6, 8, 9  success: false
[  1.0000   0.0000   0.0000][  0.0000   1.0000   0.0000][  0.0000   0.0000   1.0000]
src: 1, 2, 3, 4  dst: 0, 0, 0, 0  success: true
[  0.0000   0.0000   0.0000][  0.0000   0.0000   0.0000][  0.0000   0.0000   1.0000]
src: 1, 2, 3, 4  dst: 5, 6, 8, 9  success: true
[  1.5000   0.0000   3.5000][  0.0000   1.5000   3.0000][  0.0000   0.0000   1.0000]

See Also

MakeRectToRect ScaleToFit setPolyToPoly SkRect::isEmpty

---

MakeRectToRect

static SkMatrix MakeRectToRect(const SkRect& src, const SkRect& dst, ScaleToFit stf)

Returns Matrix set to scale and translate src Rect to dst Rect. stf selects whether mapping completely fills dst or preserves the aspect ratio, and how to align src within dst. Returns the identity Matrix if src is empty. If dst is empty, returns Matrix set to:

| 0 0 0 |
| 0 0 0 |
| 0 0 1 |

Parameters

src	Rect to map from
dst	Rect to map to
stf	one of: kFill ScaleToFit, kStart ScaleToFit, kCenter ScaleToFit, kEnd ScaleToFit

Return Value

Matrix mapping src to dst

Example

Example Output

src: 0, 0, 0, 0  dst: 0, 0, 0, 0
[  1.0000   0.0000   0.0000][  0.0000   1.0000   0.0000][  0.0000   0.0000   1.0000]
src: 0, 0, 0, 0  dst: 5, 6, 8, 9
[  1.0000   0.0000   0.0000][  0.0000   1.0000   0.0000][  0.0000   0.0000   1.0000]
src: 1, 2, 3, 4  dst: 0, 0, 0, 0
[  0.0000   0.0000   0.0000][  0.0000   0.0000   0.0000][  0.0000   0.0000   1.0000]
src: 1, 2, 3, 4  dst: 5, 6, 8, 9
[  1.5000   0.0000   3.5000][  0.0000   1.5000   3.0000][  0.0000   0.0000   1.0000]

See Also

setRectToRect ScaleToFit setPolyToPoly SkRect::isEmpty

---

setPolyToPoly

bool setPolyToPoly(const SkPoint src[], const SkPoint dst[], int count)

Sets Matrix to map src to dst. count must be zero or greater, and four or less.

If count is zero, sets Matrix to identity and returns true. If count is one, sets Matrix to translate and returns true. If count is two or more, sets Matrix to map Points if possible; returns false if Matrix cannot be constructed. If count is four, Matrix may include perspective.

Parameters

src	Points to map from
dst	Points to map to
count	number of Points in src and dst

Return Value

true if Matrix was constructed successfully

Example

See Also

setRectToRect MakeRectToRect

---

invert

bool SK_WARN_UNUSED_RESULT invert(SkMatrix* inverse) const

Sets inverse to reciprocal matrix, returning true if Matrix can be inverted. Geometrically, if Matrix maps from source to destination, inverse Matrix maps from destination to source. If Matrix can not be inverted, inverse is unchanged.

Parameters

inverse

storage for inverted Matrix; may be nullptr

Return Value

true if Matrix can be inverted

Example

See Also

Concat

---

SetAffineIdentity

static void SetAffineIdentity(SkScalar affine[6])

Fills affine with identity values in column major order. Sets affine to:

| 1 0 0 |
| 0 1 0 |

Affine 3x2 matrices in column major order are used by OpenGL and XPS.

Parameters

affine

storage for 3x2 affine matrix

Example

Example Output

ScaleX: 1 SkewY: 0 SkewX: 0 ScaleY: 1 TransX: 0 TransY: 0

See Also

setAffine asAffine

---

asAffine

bool SK_WARN_UNUSED_RESULT asAffine(SkScalar affine[6]) const

Fills affine in column major order. Sets affine to:

| scale-x  skew-x translate-x |
| skew-y  scale-y translate-y |

If Matrix contains perspective, returns false and leaves affine unchanged.

Parameters

affine

storage for 3x2 affine matrix; may be nullptr

Return Value

true if Matrix does not contain perspective

Example

Example Output

ScaleX: 2 SkewY: 5 SkewX: 3 ScaleY: 6 TransX: 4 TransY: 7

See Also

setAffine SetAffineIdentity

---

setAffine

void setAffine(const SkScalar affine[6])

Sets Matrix to affine values, passed in column major order. Given affine, column, then row, as:

| scale-x  skew-x translate-x |
|  skew-y scale-y translate-y |

Matrix is set, row, then column, to:

| scale-x  skew-x translate-x |
|  skew-y scale-y translate-y |
|       0       0           1 |

Parameters

affine

3x2 affine matrix

Example

Example Output

ScaleX: 2 SkewY: 5 SkewX: 3 ScaleY: 6 TransX: 4 TransY: 7
[  2.0000   3.0000   4.0000][  5.0000   6.0000   7.0000][  0.0000   0.0000   1.0000]

See Also

asAffine SetAffineIdentity

---

mapPoints

void mapPoints(SkPoint dst[], const SkPoint src[], int count) const

Maps src Point array of length count to dst Point array of equal or greater length. Points are mapped by multiplying each Point by Matrix. Given:

         | A B C |        | x |
Matrix = | D E F |,  pt = | y |
         | G H I |        | 1 |

where

for (i = 0; i < count; ++i) {
    x = src[i].fX
    y = src[i].fY
}

each dst Point is computed as:

              |A B C| |x|                               Ax+By+C   Dx+Ey+F
Matrix * pt = |D E F| |y| = |Ax+By+C Dx+Ey+F Gx+Hy+I| = ------- , -------
              |G H I| |1|                               Gx+Hy+I   Gx+Hy+I

src and dst may point to the same storage.

Parameters

dst	storage for mapped Points
src	Points to transform
count	number of Points to transform

Example

See Also

mapXY mapHomogeneousPoints mapVectors

---

void mapPoints(SkPoint pts[], int count) const

Maps pts Point array of length count in place. Points are mapped by multiplying each Point by Matrix. Given:

         | A B C |        | x |
Matrix = | D E F |,  pt = | y |
         | G H I |        | 1 |

where

for (i = 0; i < count; ++i) {
    x = pts[i].fX
    y = pts[i].fY
}

each resulting pts Point is computed as:

              |A B C| |x|                               Ax+By+C   Dx+Ey+F
Matrix * pt = |D E F| |y| = |Ax+By+C Dx+Ey+F Gx+Hy+I| = ------- , -------
              |G H I| |1|                               Gx+Hy+I   Gx+Hy+I

Parameters

pts	storage for mapped Points
count	number of Points to transform

Example

See Also

mapXY mapHomogeneousPoints mapVectors

---

mapHomogeneousPoints

void mapHomogeneousPoints(SkPoint3 dst[], const SkPoint3 src[], int count) const

Maps src Point3 array of length count to dst Point3 array, which must of length count or greater. Point3 array is mapped by multiplying each Point3 by Matrix. Given:

         | A B C |         | x |
Matrix = | D E F |,  src = | y |
         | G H I |         | z |

each resulting dst Point is computed as:

               |A B C| |x|
Matrix * src = |D E F| |y| = |Ax+By+Cz Dx+Ey+Fz Gx+Hy+Iz|
               |G H I| |z|

Parameters

dst	storage for mapped Point3 array
src	Point3 array to transform
count	items in Point3 array to transform

Example

See Also

mapPoints mapXY mapVectors

---

mapXY

void mapXY(SkScalar x, SkScalar y, SkPoint* result) const

Maps Point (x, y) to result. Point is mapped by multiplying by Matrix. Given:

         | A B C |        | x |
Matrix = | D E F |,  pt = | y |
         | G H I |        | 1 |

result is computed as:

              |A B C| |x|                               Ax+By+C   Dx+Ey+F
Matrix * pt = |D E F| |y| = |Ax+By+C Dx+Ey+F Gx+Hy+I| = ------- , -------
              |G H I| |1|                               Gx+Hy+I   Gx+Hy+I

Parameters

x	x-coordinate of Point to map
y	y-coordinate of Point to map
result	storage for mapped Point

Example

See Also

mapPoints mapVectors

---

SkPoint mapXY(SkScalar x, SkScalar y) const

Returns Point (x, y) multiplied by Matrix. Given:

         | A B C |        | x |
Matrix = | D E F |,  pt = | y |
         | G H I |        | 1 |

result is computed as:

              |A B C| |x|                               Ax+By+C   Dx+Ey+F
Matrix * pt = |D E F| |y| = |Ax+By+C Dx+Ey+F Gx+Hy+I| = ------- , -------
              |G H I| |1|                               Gx+Hy+I   Gx+Hy+I

Parameters

x	x-coordinate of Point to map
y	y-coordinate of Point to map

Return Value

mapped Point

Example

See Also

mapPoints mapVectors

---

mapVectors

void mapVectors(SkVector dst[], const SkVector src[], int count) const

Maps src Vector array of length count to Vector Point array of equal or greater length. Vectors are mapped by multiplying each Vector by Matrix, treating Matrix translation as zero. Given:

         | A B 0 |         | x |
Matrix = | D E 0 |,  src = | y |
         | G H I |         | 1 |

where

for (i = 0; i < count; ++i) {
    x = src[i].fX
    y = src[i].fY
}

each dst Vector is computed as:

               |A B 0| |x|                            Ax+By     Dx+Ey
Matrix * src = |D E 0| |y| = |Ax+By Dx+Ey Gx+Hy+I| = ------- , -------
               |G H I| |1|                           Gx+Hy+I   Gx+Hy+I

src and dst may point to the same storage.

Parameters

dst	storage for mapped Vectors
src	Vectors to transform
count	number of Vectors to transform

Example

See Also

mapVector mapPoints mapXY

---

void mapVectors(SkVector vecs[], int count) const

Maps vecs Vector array of length count in place, multiplying each Vector by Matrix, treating Matrix translation as zero. Given:

         | A B 0 |         | x |
Matrix = | D E 0 |,  vec = | y |
         | G H I |         | 1 |

where

for (i = 0; i < count; ++i) {
    x = vecs[i].fX
    y = vecs[i].fY
}

each result Vector is computed as:

               |A B 0| |x|                            Ax+By     Dx+Ey
Matrix * vec = |D E 0| |y| = |Ax+By Dx+Ey Gx+Hy+I| = ------- , -------
               |G H I| |1|                           Gx+Hy+I   Gx+Hy+I

Parameters

vecs	Vectors to transform, and storage for mapped Vectors
count	number of Vectors to transform

Example

See Also

mapVector mapPoints mapXY

---

mapVector

void mapVector(SkScalar dx, SkScalar dy, SkVector* result) const

Maps Vector (x, y) to result. Vector is mapped by multiplying by Matrix, treating Matrix translation as zero. Given:

         | A B 0 |         | dx |
Matrix = | D E 0 |,  vec = | dy |
         | G H I |         |  1 |

each result Vector is computed as:

               |A B 0| |dx|                                        A*dx+B*dy     D*dx+E*dy
Matrix * vec = |D E 0| |dy| = |A*dx+B*dy D*dx+E*dy G*dx+H*dy+I| = ----------- , -----------
               |G H I| | 1|                                       G*dx+H*dy+I   G*dx+*dHy+I

Parameters

dx	x-coordinate of Vector to map
dy	y-coordinate of Vector to map
result	storage for mapped Vector

Example

See Also

mapVectors mapPoints mapXY

---

SkVector mapVector(SkScalar dx, SkScalar dy) const

Returns Vector (x, y) multiplied by Matrix, treating Matrix translation as zero. Given:

         | A B 0 |         | dx |
Matrix = | D E 0 |,  vec = | dy |
         | G H I |         |  1 |

each result Vector is computed as:

               |A B 0| |dx|                                        A*dx+B*dy     D*dx+E*dy
Matrix * vec = |D E 0| |dy| = |A*dx+B*dy D*dx+E*dy G*dx+H*dy+I| = ----------- , -----------
               |G H I| | 1|                                       G*dx+H*dy+I   G*dx+*dHy+I

Parameters

dx	x-coordinate of Vector to map
dy	y-coordinate of Vector to map

Return Value

mapped Vector

Example

See Also

mapVectors mapPoints mapXY

---

mapRect

bool mapRect(SkRect* dst, const SkRect& src) const

Sets dst to bounds of src corners mapped by Matrix. Returns true if mapped corners are dst corners.

Returned value is the same as calling rectStaysRect.

Parameters

dst	storage for bounds of mapped Points
src	Rect to map

Return Value

true if dst is equivalent to mapped src

Example

See Also

mapPoints rectStaysRect

---

bool mapRect(SkRect* rect) const

Sets rect to bounds of rect corners mapped by Matrix. Returns true if mapped corners are computed rect corners.

Returned value is the same as calling rectStaysRect.

Parameters

rect	rectangle to map, and storage for bounds of mapped corners

Return Value

true if result is equivalent to mapped src

Example

See Also

mapRectScaleTranslate mapPoints rectStaysRect

---

mapRectToQuad

void mapRectToQuad(SkPoint dst[4], const SkRect& rect) const

Maps four corners of rect to dst. Points are mapped by multiplying each rect corner by Matrix. rect corner is processed in this order: (rect.fLeft, rect.fTop), (rect.fRight, rect.fTop), (rect.fRight, rect.fBottom), (rect.fLeft, rect.fBottom).

rect may be empty: rect.fLeft may be greater than or equal to rect.fRight; rect.fTop may be greater than or equal to rect.fBottom.

Given:

         | A B C |        | x |
Matrix = | D E F |,  pt = | y |
         | G H I |        | 1 |

where pt is initialized from each of (rect.fLeft, rect.fTop), (rect.fRight, rect.fTop), (rect.fRight, rect.fBottom), (rect.fLeft, rect.fBottom), each dst Point is computed as:

              |A B C| |x|                               Ax+By+C   Dx+Ey+F
Matrix * pt = |D E F| |y| = |Ax+By+C Dx+Ey+F Gx+Hy+I| = ------- , -------
              |G H I| |1|                               Gx+Hy+I   Gx+Hy+I

Parameters

dst	storage for mapped corner Points
rect	Rect to map

Example

See Also

mapRect mapRectScaleTranslate

---

mapRectScaleTranslate

void mapRectScaleTranslate(SkRect* dst, const SkRect& src) const

Sets dst to bounds of src corners mapped by Matrix. If matrix contains elements other than scale or translate: asserts if SK_DEBUG is defined; otherwise, results are undefined.

Parameters

dst	storage for bounds of mapped Points
src	Rect to map

Example

See Also

mapRect mapRectToQuad isScaleTranslate rectStaysRect

---

mapRadius

SkScalar mapRadius(SkScalar radius) const

Returns geometric mean radius of ellipse formed by constructing Circle of size radius, and mapping constructed Circle with Matrix. The result squared is equal to the major axis length times the minor axis length. Result is not meaningful if Matrix contains perspective elements.

Parameters

radius

Circle size to map

Return Value

average mapped radius

Example

The area enclosed by a square with sides equal to mappedRadius is the same as the area enclosed by the ellipse major and minor axes.

See Also

mapVector

---

isFixedStepInX

bool isFixedStepInX() const

Returns true if a unit step in x at some y mapped through Matrix can be represented by a constant Vector. Returns true if getType returns kIdentity Mask, or combinations of: kTranslate Mask, kScale Mask, and kAffine Mask.

May return true if getType returns kPerspective Mask, but only when Matrix does not include rotation or skewing along the y-axis.

Return Value

true if Matrix does not have complex perspective

Example

Example Output

[  1.0000   0.0000   0.0000][  0.0000   1.0000   0.0000][  0.0000   0.0000   1.0000]
isFixedStepInX: true
[  1.0000   0.0000   0.0000][  0.0000   2.0000   0.0000][  0.0000   0.0000   1.0000]
isFixedStepInX: true
[  1.0000   0.0000   0.0000][  0.0000   1.0000   0.0000][  0.0000   0.1000   1.0000]
isFixedStepInX: true
[  1.0000   0.0000   0.0000][  0.0000   2.0000   0.0000][  0.0000   0.1000   1.0000]
isFixedStepInX: true
[  1.0000   0.0000   0.0000][  0.0000   1.0000   0.0000][  0.1000   0.0000   1.0000]
isFixedStepInX: false
[  1.0000   0.0000   0.0000][  0.0000   2.0000   0.0000][  0.1000   0.0000   1.0000]
isFixedStepInX: false
[  1.0000   0.0000   0.0000][  0.0000   1.0000   0.0000][  0.1000   0.1000   1.0000]
isFixedStepInX: false
[  1.0000   0.0000   0.0000][  0.0000   2.0000   0.0000][  0.1000   0.1000   1.0000]
isFixedStepInX: false

See Also

fixedStepInX getType

---

fixedStepInX

SkVector fixedStepInX(SkScalar y) const

Returns Vector representing a unit step in x at y mapped through Matrix. If isFixedStepInX is false, returned value is undefined.

Parameters

y	position of line parallel to x-axis

Return Value

Vector advance of mapped unit step in x

Example

See Also

isFixedStepInX getType

---

cheapEqualTo

bool cheapEqualTo(const SkMatrix& m) const

Returns true if Matrix equals m, using an efficient comparison.

Returns false when the sign of zero values is the different; when one matrix has positive zero value and the other has negative zero value.

Returns true even when both Matrices contain NaN.

NaN never equals any value, including itself. To improve performance, NaN values are treated as bit patterns that are equal if their bit patterns are equal.

Parameters

m	Matrix to compare

Return Value

true if m and Matrix are represented by identical bit patterns

Example

Example Output

identity: a == b a.cheapEqualTo(b): true
neg zero: a == b a.cheapEqualTo(b): false
one NaN: a != b a.cheapEqualTo(b): false
both NaN: a != b a.cheapEqualTo(b): true

See Also

operator==(const SkMatrix& a, const SkMatrix& b)

---

operator==

bool operator==(const SkMatrix& a, const SkMatrix& b)

Compares a and b; returns true if a and b are numerically equal. Returns true even if sign of zero values are different. Returns false if either Matrix contains NaN, even if the other Matrix also contains NaN.

Parameters

a	Matrix to compare
b	Matrix to compare

Return Value

true if m and Matrix are numerically equal

Example

Example Output

identity: a == b a.cheapEqualTo(b): true

See Also

cheapEqualTo operator!=(const SkMatrix& a, const SkMatrix& b)

---

operator!=

bool operator!=(const SkMatrix& a, const SkMatrix& b)

Compares a and b; returns true if a and b are not numerically equal. Returns false even if sign of zero values are different. Returns true if either Matrix contains NaN, even if the other Matrix also contains NaN.

Parameters

a	Matrix to compare
b	Matrix to compare

Return Value

true if m and Matrix are numerically not equal

Example

See Also

cheapEqualTo operator==(const SkMatrix& a, const SkMatrix& b)

---

dump

void dump() const

Writes text representation of Matrix to standard output. Floating point values are written with limited precision; it may not be possible to reconstruct original Matrix from output.

Example

Example Output

[  0.7071  -0.7071   0.0000][  0.7071   0.7071   0.0000][  0.0000   0.0000   1.0000]
[  0.7071  -0.7071   0.0000][  0.7071   0.7071   0.0000][  0.0000   0.0000   1.0000]
matrix != nearlyEqual

See Also

toString

---

toString

void toString(SkString* str) const

Creates string representation of Matrix. Floating point values are written with limited precision; it may not be possible to reconstruct original Matrix from output.

Parameters

str	storage for string representation of Matrix

Example

Example Output

mStr  [  0.7071  -0.7071   0.0000][  0.7071   0.7071   0.0000][  0.0000   0.0000   1.0000]
neStr [  0.7071  -0.7071   0.0000][  0.7071   0.7071   0.0000][  0.0000   0.0000   1.0000]
matrix != nearlyEqual

See Also

dump

---

getMinScale

SkScalar getMinScale() const

Returns the minimum scaling factor of Matrix by decomposing the scaling and skewing elements. Returns -1 if scale factor overflows or Matrix contains perspective.

Return Value

minimum scale factor

Example

Example Output

matrix.getMinScale() 24

See Also

getMaxScale getMinMaxScales

---

getMaxScale

SkScalar getMaxScale() const

Returns the maximum scaling factor of Matrix by decomposing the scaling and skewing elements. Returns -1 if scale factor overflows or Matrix contains perspective.

Return Value

maximum scale factor

Example

Example Output

matrix.getMaxScale() 42

See Also

getMinScale getMinMaxScales

---

getMinMaxScales

bool SK_WARN_UNUSED_RESULT getMinMaxScales(SkScalar scaleFactors[2]) const

Sets scaleFactors[0] to the minimum scaling factor, and scaleFactors[1] to the maximum scaling factor. Scaling factors are computed by decomposing the Matrix scaling and skewing elements.

Returns true if scaleFactors are found; otherwise, returns false and sets scaleFactors to undefined values.

Parameters

scaleFactors

storage for minimum and maximum scale factors

Return Value

true if scale factors were computed correctly

Example

Example Output

matrix.getMinMaxScales() false 2 2

See Also

getMinScale getMaxScale

---

decomposeScale

bool decomposeScale(SkSize* scale, SkMatrix* remaining = nullptr) const

Decomposes Matrix into scale components and whatever remains. Returns false if Matrix could not be decomposed.

Sets scale to portion of Matrix that scales in x and y. Sets remaining to Matrix with x and y scaling factored out. remaining may be passed as nullptr to determine if Matrix can be decomposed without computing remainder.

Returns true if scale components are found. scale and remaining are unchanged if Matrix contains perspective; scale factors are not finite, or are nearly zero.

On successMatrix = scale * Remaining

Parameters

scale	x and y scaling factors; may be nullptr
remaining	Matrix without scaling; may be nullptr

Return Value

true if scale can be computed

Example

Example Output

[  0.0000  -0.2500   0.0000][  0.5000   0.0000   0.0000][  0.0000   0.0000   1.0000]
success: true  scale: 0.5, 0.25
[  0.0000  -0.5000   0.0000][  2.0000   0.0000   0.0000][  0.0000   0.0000   1.0000]
[  0.0000  -0.2500   0.0000][  0.5000   0.0000   0.0000][  0.0000   0.0000   1.0000]

See Also

setScale MakeScale

---

I

static const SkMatrix& I()

Returns reference to const identity Matrix. Returned Matrix is set to:

| 1 0 0 |
| 0 1 0 |
| 0 0 1 |

Return Value

const identity Matrix

Example

Example Output

m1 == m2
m2 == m3

See Also

reset setIdentity

---

InvalidMatrix

static const SkMatrix& InvalidMatrix()

Returns reference to a const Matrix with invalid values. Returned Matrix is set to:

| SK_ScalarMax SK_ScalarMax SK_ScalarMax |
| SK_ScalarMax SK_ScalarMax SK_ScalarMax |
| SK_ScalarMax SK_ScalarMax SK_ScalarMax |

Return Value

const invalid Matrix

Example

Example Output

scaleX 3.40282e+38

See Also

SeeAlso getType

---

Concat

static SkMatrix Concat(const SkMatrix& a, const SkMatrix& b)

Returns Matrix a multiplied by Matrix b.

Given:

    | A B C |      | J K L |
a = | D E F |, b = | M N O |
    | G H I |      | P Q R |

sets Matrix to:

        | A B C |   | J K L |   | AJ+BM+CP AK+BN+CQ AL+BO+CR |
a * b = | D E F | * | M N O | = | DJ+EM+FP DK+EN+FQ DL+EO+FR |
        | G H I |   | P Q R |   | GJ+HM+IP GK+HN+IQ GL+HO+IR |

Parameters

a	Matrix on left side of multiply expression
b	Matrix on right side of multiply expression

Return Value

Matrix computed from a times b

Example

setPolyToPoly creates perspective matrices, one the inverse of the other. Multiplying the matrix by its inverse turns into an identity matrix.

See Also

preConcat postConcat

---

dirtyMatrixTypeCache

void dirtyMatrixTypeCache()

Sets internal cache to unknown state. Use to force update after repeated modifications to Matrix element reference returned by operator[](int index).

Example

Example Output

with identity matrix: x = 24
after skew x mod:     x = 24
after 2nd skew x mod: x = 24
after dirty cache:    x = 66

See Also

operator[](int index) getType

---

setScaleTranslate

void setScaleTranslate(SkScalar sx, SkScalar sy, SkScalar tx, SkScalar ty)

Initializes Matrix with scale and translate elements.

| sx  0 tx |
|  0 sy ty |
|  0  0  1 |

Parameters

sx	horizontal scale factor to store
sy	vertical scale factor to store
tx	horizontal translation to store
ty	vertical translation to store

Example

Example Output

[  1.0000   0.0000   3.0000][  0.0000   2.0000   4.0000][  0.0000   0.0000   1.0000]

See Also

setScale preTranslate postTranslate

---

isFinite

bool isFinite() const

Returns true if all elements of the matrix are finite. Returns false if any element is infinity, or NaN.

Return Value

true if matrix has only finite elements

Example

Example Output

[  1.0000   0.0000      nan][  0.0000   1.0000   0.0000][  0.0000   0.0000   1.0000]
matrix is finite: false
matrix != matrix

See Also

operator==

---