skia2/site/user/api/SkRegion_Reference.md

SkRegion Reference

Region is a compressed one bit mask. Region describes an aliased clipping area on integer boundaries. Region can also describe an array of integer rectangles.

Canvas uses Region to reduce the current clip. Region may be drawn to Canvas; Paint determines if Region is filled or stroked, its Color, and so on.

Region may be constructed from IRect array or Path. Diagonal lines and curves in Path become integer rectangle edges. Regions operators compute union, intersection, difference, and so on. Canvas allows only intersection and difference; successive clips can only reduce available Canvas area.

---

class SkRegion {
public:
    SkRegion();
    SkRegion(const SkRegion& region);
    explicit SkRegion(const SkIRect& rect);
    ~SkRegion();
    SkRegion& operator=(const SkRegion& region);
    bool operator==(const SkRegion& other)_const;
    bool operator!=(const SkRegion& other)_const;
    bool set(const SkRegion& src);
    void swap(SkRegion& other);
    bool isEmpty() const;
    bool isRect() const;
    bool isComplex() const;
    const SkIRect& getBounds() const;
    int computeRegionComplexity() const;
    bool getBoundaryPath(SkPath* path) const;
    bool setEmpty();
    bool setRect(const SkIRect& rect);
    bool setRect(int32_t left, int32_t top, int32_t right, int32_t bottom);
    bool setRects(const SkIRect rects[], int count);
    bool setRegion(const SkRegion& region);
    bool setPath(const SkPath& path, const SkRegion& clip);
    bool intersects(const SkIRect& rect) const;
    bool intersects(const SkRegion& other) const;
    bool contains(int32_t x, int32_t y) const;
    bool contains(const SkIRect& other) const;
    bool contains(const SkRegion& other) const;
    bool quickContains(const SkIRect& r) const;
    bool quickContains(int32_t left, int32_t top, int32_t right,
                       int32_t bottom) const;
    bool quickReject(const SkIRect& rect) const;
    bool quickReject(const SkRegion& rgn) const;
    void translate(int dx, int dy);
    void translate(int dx, int dy, SkRegion* dst) const;

    enum Op {
        kDifference_Op,
        kIntersect_Op,
        kUnion_Op,
        kXOR_Op,
        kReverseDifference_Op,
        kReplace_Op,
        kLastOp = kReplace_Op,
    };

    static const int kOpCnt = kLastOp + 1;
    bool op(const SkIRect& rect, Op op);
    bool op(int left, int top, int right, int bottom, Op op);
    bool op(const SkRegion& rgn, Op op);
    bool op(const SkIRect& rect, const SkRegion& rgn, Op op);
    bool op(const SkRegion& rgn, const SkIRect& rect, Op op);
    bool op(const SkRegion& rgna, const SkRegion& rgnb, Op op);
    char* toString();

    class Iterator {
    public:
        Iterator();
        Iterator(const SkRegion& region);
        bool rewind();
        void reset(const SkRegion& region);
        bool done() const;
        void next();
        const SkIRect& rect() const;
        const SkRegion* rgn() const;
    };

    class Cliperator {
    public:
        Cliperator(const SkRegion& region, const SkIRect& clip);
        bool done();
        void next();
        const SkIRect& rect() const;
    };

    class Spanerator {
    public:
        Spanerator(const SkRegion& region, int y, int left, int right);
        bool next(int* left, int* right);
    };

    size_t writeToMemory(void* buffer) const;
    size_t readFromMemory(const void* buffer, size_t length);
};

SkRegion describes the set of pixels used to clip Canvas. SkRegion is compact, efficiently storing a single integer rectangle, or a run length encoded array of rectangles. SkRegion may reduce the current Canvas Clip, or may be drawn as one or more integer rectangles. SkRegion iterator returns the scan lines or rectangles contained by it, optionally intersecting a bounding rectangle.

---

    class Iterator {
    public:
        Iterator();
        Iterator(const SkRegion& region);
        bool rewind();
        void reset(const SkRegion& region);
        bool done() const;
        void next();
        const SkIRect& rect();
        const SkRegion* rgn();
    };

Returns sequence of rectangles, sorted along y-axis, then x-axis, that make up Region.

---

Iterator()

Initializes Iterator with an empty Region. done() on Iterator returns true. Call reset() to initialized Iterator at a later time.

Return Value

empty Region ierator

Example

Example Output

rect={1,2,3,4}

See Also

reset SkRegion

---

Iterator(const SkRegion& region)

Sets Iterator to return elements of IRect array in region.

Parameters

region

Region to iterate

Return Value

Region iterator

Example

Example Output

rect={1,2,3,4}

See Also

reset SkRegion Cliperator Spanerator

---

bool rewind()

Points Iterator to start of Region. Returns true if Region was set; otherwise, returns false.

Return Value

true if Region was set

Example

Example Output

#Volatile
empty iter rewind success=false
empty iter rect={0,0,0,0}
empty region rewind success=true
empty region rect={0,0,0,0}
after set rect rect={1,2,3,4}
after rewind rewind success=true
after rewind rect={1,2,3,4}

See Also

reset

---

void reset(const SkRegion& region)

Resets iterator, using the new Region.

Parameters

region

Region to iterate

Example

Example Output

empty region: done=true
after set rect: done=true
after reset: done=false

See Also

rewind

---

bool done() const

Returns true if Iterator is pointing to final IRect in Region.

Return Value

true if data parsing is complete

Example

Example Output

done=true
done=false

See Also

next rect

---

void next()

Advances Iterator to next IRect in Region if it is not done.

Example

Example Output

rect={1,2,3,4}
rect={5,6,7,8}

See Also

done rect

---

const SkIRect& rect() const

Returns IRect element in Region. Does not return predictable results if Region is empty.

Return Value

part of Region as IRect

Example

Example Output

#Volatile
rect={0,0,0,0}
rect={1,2,3,4}

See Also

next done

---

const SkRegion* rgn() const

Returns Region if set; otherwise, returns nullptr.

Return Value

iterated Region

Example

See Also

Iterator reset

---

    class SK_API Cliperator {
    public:
        Cliperator(const SkRegion& region, const SkIRect& clip);
        bool done();
        void next();
        const SkIRect& rect() const;
    };

Returns the sequence of rectangles, sorted along y-axis, then x-axis, that make up Region intersected with the specified clip rectangle.

---

Cliperator(const SkRegion& region, const SkIRect& clip)

Sets Cliperator to return elements of IRect array in Region within clip.

Parameters

region	Region to iterate
clip	bounds of iteration

Return Value

Region iterator

Example

Example Output

rect={1,2,2,3}

See Also

SkRegion Iterator Spanerator

---

bool done()

Returns true if Cliperator is pointing to final IRect in Region.

Return Value

true if data parsing is complete

Example

Example Output

empty region done=true
after add rect done=false

See Also

next rect

---

void  next()

Advances iterator to next IRect in Region contained by clip.

Example

Example Output

rect={1,3,3,4}
rect={5,6,7,7}

See Also

done

---

const SkIRect& rect() const

Returns IRect element in Region, intersected with clip passed to Cliperator constructor. Does not return predictable results if Region is empty.

Return Value

part of Region inside clip as IRect

Example

Example Output

#Volatile
empty region rect={1094713344,1065353216,0,-1}
after set rect rect={1,2,3,3}

See Also

next done

---

    class Spanerator {
    public:
        Spanerator(const SkRegion& region, int y, int left, int right);
        bool next(int* left, int* right);
    };

Returns the line segment ends within Region that intersect a horizontal line.

---

Spanerator(const SkRegion& region, int y, int left, int right)

Sets Spanerator to return line segments in Region on scan line.

Parameters

region	Region to iterate
y	horizontal line to intersect
left	bounds of iteration
right	bounds of iteration

Return Value

Region iterator

Example

See Also

SkRegion Iterator Cliperator

---

bool next(int* left, int* right)

Advances iterator to next span intersecting Region within line segment provided in constructor. Returns true if interval was found.

Parameters

left	pointer to span start; may be nullptr
right	pointer to span end; may be nullptr

Return Value

true if interval was found

Example

Example Output

empty region: result=false
after set rect: result=true left=2 right=3

See Also

done

---

SkRegion()

Constructs an empty Region. Region is set to empty bounds at (0, 0) with zero width and height.

Return Value

empty Region

Example

Example Output

region bounds: {0, 0, 0, 0}

See Also

setEmpty

---

SkRegion(const SkRegion& region)

Constructs a copy of an existing region. Copy constructor makes two regions identical by value. Internally, region and the returned result share pointer values. The underlying Rect array is copied when modified.

Creating a Region copy is very efficient and never allocates memory. Regions are always copied by value from the interface; the underlying shared pointers are not exposed.

Parameters

region

Region to copy by value

Return Value

copy of Region

Example

Example Output

region bounds: {1,2,3,4}
region2 bounds: {1,2,3,4}
after region set empty:
region bounds: {0,0,0,0}
region2 bounds: {1,2,3,4}

See Also

setRegion operator=(const SkRegion& region)

---

explicit SkRegion(const SkIRect& rect)

Constructs a rectangular Region matching the bounds of rect.

Parameters

rect	bounds of constructed Region

Return Value

rectangular Region

Example

See Also

setRect^[2] setRegion

---

~SkRegion()

Releases ownership of any shared data and deletes data if Region is sole owner.

Example

delete calls Region Destructor, but copy of original in region2 is unaffected.

Example Output

region2 bounds: {1,2,3,4}

See Also

SkRegion() SkRegion(const SkRegion& region) SkRegion(const SkIRect& rect) operator=(const SkRegion& region)

---

SkRegion& operator=(const SkRegion& region)

Constructs a copy of an existing region. Makes two regions identical by value. Internally, region and the returned result share pointer values. The underlying Rect array is copied when modified.

Creating a Region copy is very efficient and never allocates memory. Regions are always copied by value from the interface; the underlying shared pointers are not exposed.

Parameters

region

Region to copy by value

Return Value

Region to copy by value

Example

Example Output

region1 bounds: {1,2,3,4}
region2 bounds: {1,2,3,4}

See Also

set swap SkRegion(const SkRegion& region)

---

bool operator==(const SkRegion& other) const

Compares Region and other; returns true if they enclose exactly the same area.

Parameters

other

Region to compare

Return Value

true if Region pair are equivalent

Example

Example Output

empty one == two
set rect one != two
set empty one == two

See Also

operator!=(const SkRegion& other) const operator=(const SkRegion& region)

---

bool operator!=(const SkRegion& other) const

Compares Region and other; returns true if they do not enclose the same area.

Parameters

other

Region to compare

Return Value

true if Region pair are not equivalent

Example

Example Output

empty one == two
set rect one != two
union rect one == two

See Also

operator==(const SkRegion& other) const operator=(const SkRegion& region)

---

bool set(const SkRegion& src)

Sets Region to src, and returns true if src bounds is not empty. This makes Region and src identical by value. Internally, Region and src share pointer values. The underlying Rect array is copied when modified.

Creating a Region copy is very efficient and never allocates memory. Regions are always copied by value from the interface; the underlying shared pointers are not exposed.

Parameters

src	Region to copy

Return Value

copy of src

Example

Example Output

region1 bounds: {1,2,3,4}
region2 bounds: {1,2,3,4}

See Also

operator=(const SkRegion& region) swap SkRegion(const SkRegion& region)

---

void swap(SkRegion& other)

Exchanges IRect array of Region and other. swap() internally exchanges pointers, so it is lightweight and does not allocate memory.

swap() usage has largely been replaced by operator=(const SkRegion& region). Paths do not copy their content on assignment until they are written to, making assignment as efficient as swap().

Parameters

other

operator=(const SkRegion& region) set

Example

Example Output

region1 bounds: {0,0,0,0}
region2 bounds: {1,2,3,4}

See Also

operator=(const SkRegion& region) set SkRegion(const SkRegion& region)

---

bool isEmpty() const

Returns true if Region is empty. Empty Region has bounds width or height less than or equal to zero. SkRegion() constructs empty Region; setEmpty and setRect with dimensionless data make Region empty.

Return Value

true if bounds has no width or height

Example

Example Output

initial: region is empty
set rect: region is not empty
set empty: region is empty

See Also

isRect isComplex operator==(const SkRegion& other) const

---

bool isRect() const

Returns true if Region is one IRect with positive dimensions.

Return Value

true if Region contains one IRect

Example

Example Output

initial: region is not rect
set rect: region is rect
set empty: region is not rect

See Also

isEmpty isComplex

---

bool isComplex() const

Returns true if Region is described by more than one rectangle.

Return Value

true if Region contains more than one IRect

Example

Example Output

initial: region is not complex
set rect: region is not complex
op rect: region is complex

See Also

isEmpty isRect

---

const SkIRect& getBounds() const

Returns minimum and maximum axes values of IRect array. Returns (0, 0, 0, 0) if Region is empty.

Return Value

combined bounds of all IRect elements

Example

Example Output

bounds: {1,2,4,5}

See Also

isEmpty isRect

---

int computeRegionComplexity() const

Returns a value that increases with the number of elements in Region. Returns zero if Region is empty. Returns one if Region equals IRect; otherwise, returns value greater than one indicating that Region is complex.

Call to compare Regions for relative complexity.

Return Value

relative complexity

Example

Example Output

initial: region complexity 0
set rect: region complexity 1
op rect: region complexity 3

See Also

isRect isComplex

---

bool getBoundaryPath(SkPath* path) const

Appends outline of Region to path. Returns true if Region is not empty; otherwise, returns false, and leaves path unmodified.

Parameters

path	Path to append to

Return Value

true if path changed

Example

See Also

isEmpty isComplex

---

bool setEmpty()

Constructs an empty Region. Region is set to empty bounds at (0, 0) with zero width and height. Always returns false.

Return Value

false

Example

Example Output

region bounds: {1,2,3,4}
after region set empty:
region bounds: {0,0,0,0}

See Also

SkRegion()

---

bool setRect(const SkIRect& rect)

Constructs a rectangular Region matching the bounds of rect. If rect is empty, constructs empty and returns false.

Parameters

rect	bounds of constructed Region

Return Value

true if rect is not empty

Example

Example Output

region is not empty
region is empty
setEmpty: false

See Also

SkRegion(const SkIRect& rect)

---

bool setRect(int32_t left, int32_t top, int32_t right, int32_t bottom)

Constructs Region with bounds (left, top, right, bottom). Returns true if left is less than right and top is less than bottom; otherwise, constructs empty Region and returns false.

Parameters

left	edge of bounds on x-axis
top	edge of bounds on y-axis
right	edge of bounds on x-axis
bottom	edge of bounds on y-axis

Return Value

rectangular Region

Example

Example Output

set to: 1,2,3,4: success:true {1,2,3,4}
set to: 3,2,1,4: success:false {0,0,0,0}

See Also

SkRegion(const SkIRect& rect)

---

bool setRects(const SkIRect rects[], int count)

Constructs Region as the union of IRect in rects array. If count is zero, constructs empty Region. Returns false if constructed Region is empty.

May be faster than repeated calls to op().

Parameters

rects	array of IRects
count	array size

Return Value

true if constructed Region is not empty

Example

See Also

setRect^[2] op^{[2][3][4][5][6]}

---

bool setRegion(const SkRegion& region)

Constructs a copy of an existing region. Makes two regions identical by value. Internally, region and the returned result share pointer values. The underlying Rect array is copied when modified.

Creating a Region copy is very efficient and never allocates memory. Regions are always copied by value from the interface; the underlying shared pointers are not exposed.

Parameters

region

Region to copy by value

Return Value

Region to copy by value

Example

Example Output

region bounds: {1,2,3,4}
region2 bounds: {1,2,3,4}
after region set empty:
region bounds: {1,2,3,4}
region2 bounds: {0,0,0,0}

See Also

SkRegion(const SkRegion& region)

---

bool setPath(const SkPath& path, const SkRegion& clip)

Constructs Region to match outline of path within clip. Returns false if constructed Region is empty.

Constructed Region draws the same pixels as path through clip when Anti Aliasing is disabled.

Parameters

path	Path providing outline
clip	Region containing path

Return Value

true if constructed Region is not empty

Example

See Also

setRects op^{[2][3][4][5][6]}

---

bool intersects(const SkIRect& rect) const

Returns true if Region intersects rect. Returns false if either rect or Region is empty, or do not intersect.

Parameters

rect	IRect to intersect

Return Value

true if rect and Region have area in common

Example

See Also

contains^[2][3] SkRect::intersects^[2]

---

bool intersects(const SkRegion& other) const

Returns true if Region intersects other. Returns false if either other or Region is empty, or do not intersect.

Parameters

other

Region to intersect

Return Value

true if other and Region have area in common

Example

See Also

contains^[2][3] SkRect::intersects^[2]

---

bool contains(int32_t x, int32_t y) const

Returns true if IPoint (x, y) is inside Region. Returns false if Region is empty.

Parameters

x	test IPoint x-coordinate
y	test IPoint y-coordinate

Return Value

true if (x, y) is inside Region

Example

See Also

intersects^[2] SkRect::contains^[2][3]

---

bool contains(const SkIRect& other) const

Returns true if other is completely inside Region. Returns false if Region or other is empty.

Parameters

other

IRect to contain

Return Value

true if other is inside Region

Example

See Also

intersects^[2] SkRect::contains^[2][3]

---

bool contains(const SkRegion& other) const

Returns true if other is completely inside Region. Returns false if Region or other is empty.

Parameters

other

Region to contain

Return Value

true if other is inside Region

Example

See Also

intersects^[2] SkRect::contains^[2][3]

---

bool quickContains(const SkIRect& r) const

Returns true if Region is a single rectangle and contains r. May return false even though Region contains r.

Parameters

r	IRect to contain

Return Value

true quickly if r points are equal or inside

Example

Example Output

quickContains 1: true
quickContains 2: true
quickContains 3: false

See Also

contains^[2][3] quickReject^[2] intersects^[2]

---

bool quickContains(int32_t left, int32_t top, int32_t right, int32_t bottom) const

Returns true if Region is a single rectangle and contains IRect (left, top, right, bottom). Returns false if Region is empty or IRect (left, top, right, bottom) is empty. May return false even though Region contains (left, top, right, bottom).

Parameters

left	edge of bounds on x-axis
top	edge of bounds on y-axis
right	edge of bounds on x-axis
bottom	edge of bounds on y-axis

Return Value

true quickly if IRect are equal or inside

Example

Example Output

quickContains 1: true
quickContains 2: true
quickContains 3: false

See Also

contains^[2][3] quickReject^[2] intersects^[2]

---

bool quickReject(const SkIRect& rect) const

Returns true if Region does not intersect rect. Returns true if rect is empty or Region is empty. May return false even though Region does not intersect rect.

Parameters

rect	IRect to intersect

Return Value

true if rect does not intersect

Example

Example Output

quickReject 1: true
quickReject 2: true
quickReject 3: false

See Also

quickContains^[2] contains^[2][3] intersects^[2]

---

bool quickReject(const SkRegion& rgn) const

Returns true if Region does not intersect rgn. Returns true if rgn is empty or Region is empty. May return false even though Region does not intersect rgn.

Parameters

rgn	Region to intersect

Return Value

true if rgn does not intersect

Example

Example Output

quickReject 1: true
quickReject 2: true
quickReject 3: false

See Also

quickContains^[2] contains^[2][3] intersects^[2]

---

void translate(int dx, int dy)

Offsets Region by IVector (dx, dy). Has no effect if Region is empty.

Parameters

dx	x-axis offset
dy	y-axis offset

Example

See Also

SkCanvas::translate SkIRect::offset^[2] SkPath::offset^[2]

---

void translate(int dx, int dy, SkRegion* dst) const

Offsets Region by IVector (dx, dy), writing result to dst. Region may be passed as dst parameter, translating Region in place. Has no effect if dst is nullptr. If Region is empty, sets dst to empty.

Parameters

dx	x-axis offset
dy	y-axis offset
dst	translated result

Example

See Also

SkCanvas::translate SkIRect::offset^[2] SkPath::offset^[2]

---

    enum Op {
        kDifference_Op,
        kIntersect_Op,
        kUnion_Op,
        kXOR_Op,
        kReverseDifference_Op,
        kReplace_Op,
        kLastOp = kReplace_Op,
    };

The logical operations that can be performed when combining two Regions.

Constants

Const	Value	Description
SkRegion::kDifference_Op	0	Subtracts operand Region from target Region.
SkRegion::kIntersect_Op	1	Intersects operand Region and target Region.
SkRegion::kUnion_Op	2	Unions operand Region and target Region.
SkRegion::kXOR_Op	3	Replaces target Region with area exclusive to both Regions.
SkRegion::kReverseDifference_Op	4	Subtracts target Region from operand Region.
SkRegion::kReplace_Op	5	Replaces target Region with operand Region.
SkRegion::kLastOp	5	last operator

Example

See Also

SkPathOp

Constants

Const	Value	Description
SkRegion::kOpCnt	6	May be used to verify that Op is a legal value.

---

bool op(const SkIRect& rect, Op op)

Replaces Region with the result of Region op rect. Returns true if replaced Region is not empty.

Parameters

rect	IRect operand
op	operator, one of: kDifference Op, kIntersect Op, kUnion Op, kXOR Op, kReverseDifference Op, kReplace Op

Return Value

false if result is empty

Example

See Also

setRects Op

---

bool op(int left, int top, int right, int bottom, Op op)

Replaces Region with the result of Region op IRect (left, top, right, bottom). Returns true if replaced Region is not empty.

Parameters

left	edge of bounds on x-axis
top	edge of bounds on y-axis
right	edge of bounds on x-axis
bottom	edge of bounds on y-axis
op	operator, one of: kDifference Op, kIntersect Op, kUnion Op, kXOR Op, kReverseDifference Op, kReplace Op

Return Value

false if result is empty

Example

See Also

setRects Op

---

bool op(const SkRegion& rgn, Op op)

Replaces Region with the result of Region op rgn. Returns true if replaced Region is not empty.

Parameters

rgn	Region operand
op	operator, one of: kDifference Op, kIntersect Op, kUnion Op, kXOR Op, kReverseDifference Op, kReplace Op

Return Value

false if result is empty

Example

See Also

setRects Op

---

bool op(const SkIRect& rect, const SkRegion& rgn, Op op)

Replaces Region with the result of rect op rgn. Returns true if replaced Region is not empty.

Parameters

rect	IRect operand
rgn	Region operand
op	operator, one of: kDifference Op, kIntersect Op, kUnion Op, kXOR Op, kReverseDifference Op, kReplace Op

Return Value

false if result is empty

Example

See Also

setRects Op

---

bool op(const SkRegion& rgn, const SkIRect& rect, Op op)

Replaces Region with the result of rgn op rect. Returns true if replaced Region is not empty.

Parameters

rgn	Region operand
rect	IRect operand
op	operator, one of: kDifference Op, kIntersect Op, kUnion Op, kXOR Op, kReverseDifference Op, kReplace Op

Return Value

false if result is empty

Example

See Also

setRects Op

---

bool op(const SkRegion& rgna, const SkRegion& rgnb, Op op)

Replaces Region with the result of rgna op rgnb. Returns true if replaced Region is not empty.

Parameters

rgna	Region operand
rgnb	Region operand
op	operator, one of: kDifference Op, kIntersect Op, kUnion Op, kXOR Op, kReverseDifference Op, kReplace Op

Return Value

false if result is empty

Example

See Also

setRects Op

---

char* toString()

Private: Android framework only.

Return Value

string representation of Region

---

size_t writeToMemory(void* buffer) const

Writes Region to buffer, and returns number of bytes written. If buffer is nullptr, returns number number of bytes that would be written.

Parameters

buffer

storage for binary data

Return Value

size of Region

Example

See Also

readFromMemory

---

size_t readFromMemory(const void* buffer, size_t length)

Constructs Region from buffer of size length. Returns bytes read. Returned value will be multiple of four or zero if length was too small.

Parameters

buffer	storage for binary data
length	size of buffer

Return Value

bytes read

Example

See Also

writeToMemory