skia2/site/user/api/SkImageInfo_Reference.md

SkImageInfo Reference

Image Info

Image Info specifies the dimensions and encoding of the pixels in a Bitmap. The dimensions are integral width and height. The encoding is how pixel bits describe Color Alpha, transparency; Color components red, blue, and green; and Color Space, the range and linearity of colors.

Image Info describes an uncompressed raster pixels. In contrast, Image additionally describes compressed pixels like PNG, and Surface describes destinations on the GPU. Image and Surface may be specified by Image Info, but Image and Surface may not contain Image Info.

Overview

Overview Subtopic

name	description
Constructor	functions that construct SkImageInfo
Member Function	static functions and member methods
Operator	operator overloading methods
Related Function	similar methods grouped together

Constant

name	description

Alpha Type

Enum SkAlphaType

enum SkAlphaType {
kUnknown_SkAlphaType,
kOpaque_SkAlphaType,
kPremul_SkAlphaType,
kUnpremul_SkAlphaType,
kLastEnum_SkAlphaType = kUnpremul_SkAlphaType,
};

Describes how to interpret the alpha component of a pixel. A pixel may be opaque, or Color Alpha, describing multiple levels of transparency.

In simple blending, Color Alpha weights the draw color and the destination color to create a new color. If alpha describes a weight from zero to one:

new color = draw color * alpha + destination color * (1 - alpha)In practice alpha is encoded in two or more bits, where 1.0 equals all bits set.

Color RGB may have Color Alpha included in each component value; the stored value is the original Color RGB multiplied by Color Alpha. Premultiplied color components improve performance.

Constants

kUnknown_SkAlphaType	0	Alpha Type is uninitialized.
kOpaque_SkAlphaType	1	Pixels are opaque. The Color Type must have no explicit alpha component, or all alpha components must be set to their maximum value.
kPremul_SkAlphaType	2	Pixels have alpha premultiplied into color components. Surface pixels must be premultiplied.
kUnpremul_SkAlphaType	3	Pixel color component values are independent of alpha value. Images generated from encoded data like PNG do not premultiply pixel color components. kUnpremul_SkAlphaType is supported for Image pixels, but not for Surface pixels.

See Also

SkColorType SkColorSpace

Alpha Type Opaque

Use Opaque as a hint to optimize drawing when alpha component of all pixel is set to its maximum value of 1.0; all alpha component bits are set. If Image Info is set to Opaque but all alpha values are not 1.0, results are undefined.

Example

SkPreMultiplyARGB parameter a is set to 255, its maximum value, and is interpreted as Color Alpha of 1.0. kOpaque_SkAlphaType may be set to improve performance. If SkPreMultiplyARGB parameter a is set to a value smaller than 255, kPremul_SkAlphaType must be used instead to avoid undefined results. The four displayed values are the original component values, though not necessarily in the same order.

Alpha Type Premul

Use Premul when stored color components are the original color multiplied by the alpha component. The alpha component range of 0.0 to 1.0 is achieved by dividing the integer bit value by the maximum bit value.

stored color = original color * alpha / max alphaThe color component must be equal to or smaller than the alpha component, or the results are undefined.

Example

SkPreMultiplyARGB parameter a is set to 150, less than its maximum value, and is interpreted as Color Alpha of about 0.6. kPremul_SkAlphaType must be set, since SkPreMultiplyARGB parameter a is set to a value smaller than 255, to avoid undefined results. The four displayed values reflect that the alpha component has been multiplied by the original color.

Alpha Type Unpremul

Use Unpremul if stored color components are not divided by the alpha component. Some drawing destinations may not support Unpremul.

Example

SkColorSetARGB parameter a is set to 150, less than its maximum value, and is interpreted as Color Alpha of about 0.6. color is not premultiplied; color components may have values greater than color alpha. The four displayed values are the original component values, though not necessarily in the same order.

Color Type

Color Type Native

Enum SkColorType

enum SkColorType {
kUnknown_SkColorType,
kAlpha_8_SkColorType,
kRGB_565_SkColorType,
kARGB_4444_SkColorType,
kRGBA_8888_SkColorType,
kRGB_888x_SkColorType,
kBGRA_8888_SkColorType,
kRGBA_1010102_SkColorType,
kRGB_101010x_SkColorType,
kGray_8_SkColorType,
kRGBA_F16_SkColorType,
kLastEnum_SkColorType = kRGBA_F16_SkColorType,
kN32_SkColorType = kBGRA_8888_SkColorType,
kN32_SkColorType = kRGBA_8888_SkColorType,
};

Describes how pixel bits encode color. A pixel may be an alpha mask, a gray level, Color RGB, or Color ARGB.

kN32_SkColorType selects the native 32-bit Color ARGB format. On Little_Endian processors, pixels containing 8-bit Color ARGB components pack into 32-bit kBGRA_8888_SkColorType. On Big_Endian processors, pixels pack into 32-bit kRGBA_8888_SkColorType.

Constants

kUnknown_SkColorType	0
kAlpha_8_SkColorType	1	Encodes Color Alpha as Alpha 8 pixel in an 8-bit byte.
kRGB_565_SkColorType	2	Encodes Color RGB as BGR 565 pixel in a 16-bit word.
kARGB_4444_SkColorType	3	Encodes Color ARGB as ABGR 4444 pixel in a 16-bit word.
kRGBA_8888_SkColorType	4	Encodes Color ARGB as RGBA 8888 pixel in a 32-bit word.
kRGB_888x_SkColorType	5	Encodes Color RGB as RGB 888x pixel in a 32-bit word.
kBGRA_8888_SkColorType	6	Encodes Color ARGB as BGRA 8888 pixel in a 32-bit word.
kRGBA_1010102_SkColorType	7	Encodes Color ARGB as RGBA 1010102 pixel in a 32-bit word.
kRGB_101010x_SkColorType	8	Encodes Color RGB as RGB 101010x pixel in a 32-bit word.
kGray_8_SkColorType	9	Encodes Color Gray as Gray 8 in an 8-bit byte.
kRGBA_F16_SkColorType	10	Encodes Color ARGB as RGBA F16 in a 64-bit word.

Constants

kN32_SkColorType

4

Encodes Color ARGB as either RGBA 8888 or BGRA 8888, whichever is native to the platform.

See Also

SkAlphaType SkColorSpace

Color Type Alpha 8

Alpha 8 is an 8-bit byte pixel encoding that represents transparency. A value of zero is completely transparent; a value of 255 is completely opaque. Bitmap with Alpha 8 pixels does not visibly draw, because its pixels have no color information. The paired SkAlphaType is ignored.

Example

Alpha 8 pixels can modify another draw. orangePaint fills the bounds of bitmap, with its transparency set to alpha8 pixel value.

Color Type BGR 565

BGR 565 is a 16-bit word pixel encoding that contains five bits of blue, six bits of green, and five bits of red. BGR 565 is fully opaque as if its Color Alpha was set to one, and should always be paired with kOpaque_SkAlphaType.

Example

Color Type ABGR 4444

ABGR 4444 is a 16-bit word pixel encoding that contains four bits of alpha, four bits of blue, four bits of green, and four bits of red.

If paired with kPremul_SkAlphaType: blue, green, and red components are premultiplied by the alpha value. If blue, green, or red is greater than alpha, the drawn result is undefined.

If paired with kUnpremul_SkAlphaType: alpha, blue, green, and red components may have any value. There may be a performance penalty with unpremultipled pixels.

If paired with kOpaque_SkAlphaType: all alpha component values are at the maximum; blue, green, and red components are fully opaque. If any alpha component is less than 15, the drawn result is undefined.

Example

Color Type RGBA 8888

RGBA 8888 is a 32-bit word pixel encoding that contains eight bits of red, eight bits of green, eight bits of blue, and eight bits of alpha.

If paired with kPremul_SkAlphaType: red, green, and blue components are premultiplied by the alpha value. If red, green, or blue is greater than alpha, the drawn result is undefined.

If paired with kUnpremul_SkAlphaType: alpha, red, green, and blue components may have any value. There may be a performance penalty with unpremultipled pixels.

If paired with kOpaque_SkAlphaType: all alpha component values are at the maximum; red, green, and blue components are fully opaque. If any alpha component is less than 255, the drawn result is undefined.

On Big_Endian platforms, RGBA 8888 is the native Color Type, and will have the best performance. Use kN32_SkColorType to choose the best Color Type for the platform at compile time.

Example

Color Type RGB 888x

RGB 888x is a 32-bit word pixel encoding that contains eight bits of red, eight bits of green, eight bits of blue, and eight unused bits. RGB 888x is fully opaque as if its Color Alpha was set to one, and should always be paired with kOpaque_SkAlphaType.

Example

Color Type BGRA 8888

BGRA 8888 is a 32-bit word pixel encoding that contains eight bits of blue, eight bits of green, eight bits of red, and eight bits of alpha.

If paired with kPremul_SkAlphaType: blue, green, and red components are premultiplied by the alpha value. If blue, green, or red is greater than alpha, the drawn result is undefined.

If paired with kUnpremul_SkAlphaType: blue, green, red, and alpha components may have any value. There may be a performance penalty with unpremultipled pixels.

If paired with kOpaque_SkAlphaType: all alpha component values are at the maximum; blue, green, and red components are fully opaque. If any alpha component is less than 255, the drawn result is undefined.

On Little_Endian platforms, BGRA 8888 is the native Color Type, and will have the best performance. Use kN32_SkColorType to choose the best Color Type for the platform at compile time.

Example

Color Type RGBA 1010102

RGBA 1010102 is a 32-bit word pixel encoding that contains ten bits of red, ten bits of green, ten bits of blue, and two bits of alpha. Possible alpha values are zero: fully transparent; one: 33% opaque; two: 67% opaque; three: fully opaque.

If paired with kPremul_SkAlphaType: red, green, and blue components are premultiplied by the alpha value. If red, green, or blue is greater than the alpha replicated to ten bits, the drawn result is undefined.

If paired with kUnpremul_SkAlphaType: alpha, red, green, and blue components may have any value. There may be a performance penalty with unpremultipled pixels.

If paired with kOpaque_SkAlphaType: all alpha component values are at the maximum; red, green, and blue components are fully opaque. If any alpha component is less than 3, the drawn result is undefined.

Example

Color Type RGB 101010x

Example

Color Type Gray 8

Example

Color Type RGBA F16

Example

YUV ColorSpace

Enum SkYUVColorSpace

enum SkYUVColorSpace {
kJPEG_SkYUVColorSpace,
kRec601_SkYUVColorSpace,
kRec709_SkYUVColorSpace,
kLastEnum_SkYUVColorSpace = kRec709_SkYUVColorSpace,
};

Describes the color space a YUV pixel.

Constants

kJPEG_SkYUVColorSpace	0	Standard JPEG color space.
kRec601_SkYUVColorSpace	1	SDTV standard Rec. 601 color space. Uses "studio swing" [16, 235] color range. See http://en.wikipedia.org/wiki/Rec._601 for details.
kRec709_SkYUVColorSpace	2	HDTV standard Rec. 709 color space. Uses "studio swing" [16, 235] color range. See http://en.wikipedia.org/wiki/Rec._709 for details.

Example

See Also

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Enum SkDestinationSurfaceColorMode

enum class SkDestinationSurfaceColorMode {
kLegacy,
kGammaAndColorSpaceAware,
};

Constants

SkDestinationSurfaceColorMode::kLegacy	0
SkDestinationSurfaceColorMode::kGammaAndColorSpaceAware	1

Example

See Also

incomplete

Struct SkImageInfo

Describes Image dimensions and pixel type. Used for both source images and render-targets (surfaces).

Member Function

name	description
ByteSizeOverflowed	incomplete
Make	creates Image Info from dimensions, Color Type, Alpha Type, Color Space
MakeA8	creates Image Info with kAlpha_8_SkColorType, kPremul_SkAlphaType
MakeN32	creates Image Info with Native Color Type
MakeN32Premul	creates Image Info with Native Color Type, kPremul_SkAlphaType
MakeS32	creates Image Info with Native Color Type, sRGB Color Space
MakeUnknown	creates Image Info with kUnknown_SkColorType, kUnknown_SkAlphaType
alphaType	incomplete
bounds	incomplete
bytesPerPixel	incomplete
colorSpace	incomplete
colorType	incomplete
computeByteSize	incomplete
computeMinByteSize	incomplete
computeOffset	incomplete
dimensions	incomplete
flatten	incomplete
gammaCloseToSRGB	incomplete
height	incomplete
isEmpty	incomplete
isOpaque	incomplete
makeAlphaType	creates Image Info with changed Alpha Type
makeColorSpace	creates Image Info with changed Color Space
makeColorType	creates Image Info with changed Color Type
makeWH	creates Image Info with changed dimensions
minRowBytes	incomplete
minRowBytes64	incomplete
refColorSpace	incomplete
reset	incomplete
shiftPerPixel	incomplete
unflatten	incomplete
validRowBytes	incomplete
validate	incomplete
width	incomplete

Related Function

name	description
Property	metrics and attributes
Utility	rarely called management functions

Constructor

name	description
Make	creates Image Info from dimensions, Color Type, Alpha Type, Color Space
MakeA8	creates Image Info with kAlpha_8_SkColorType, kPremul_SkAlphaType
MakeN32	creates Image Info with Native Color Type
MakeN32Premul	creates Image Info with Native Color Type, kPremul_SkAlphaType
	MakeN32Premul(int width, int height, sk sp<SkColorSpace> cs = nullptr)
	MakeN32Premul(const SkISize& size)
MakeS32	creates Image Info with Native Color Type, sRGB Color Space
MakeUnknown	creates Image Info with kUnknown_SkColorType, kUnknown_SkAlphaType
	MakeUnknown(int width, int height)
	MakeUnknown()
SkImageInfo()	creates with zero dimensions, kUnknown_SkColorType, kUnknown_SkAlphaType
makeAlphaType	creates Image Info with changed Alpha Type
makeColorSpace	creates Image Info with changed Color Space
makeColorType	creates Image Info with changed Color Type
makeWH	creates Image Info with changed dimensions
reset	incomplete

SkImageInfo

SkImageInfo()

Return Value

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Example

See Also

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Make

static SkImageInfo Make(int width, int height, SkColorType ct, SkAlphaType at,
                        sk_sp<SkColorSpace> cs = nullptr)

Parameters

width	incomplete
height	incomplete
ct	incomplete
at	incomplete
cs	incomplete

Return Value

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Example

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MakeN32

static SkImageInfo MakeN32(int width, int height, SkAlphaType at, sk_sp<SkColorSpace> cs = nullptr)

Sets Color Type to kN32_SkColorType.

Parameters

width	incomplete
height	incomplete
at	incomplete
cs	incomplete

Return Value

incomplete

Example

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MakeS32

static SkImageInfo MakeS32(int width, int height, SkAlphaType at)

Creates Image Info marked as sRGB with kN32_SkColorType swizzle.

Parameters

width	incomplete
height	incomplete
at	incomplete

Return Value

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Example

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MakeN32Premul

static SkImageInfo MakeN32Premul(int width, int height, sk_sp<SkColorSpace> cs = nullptr)

Sets Color Type to kN32_SkColorType, and the Alpha Type to kPremul_SkAlphaType.

Parameters

width	incomplete
height	incomplete
cs	incomplete

Return Value

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Example

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---

static SkImageInfo MakeN32Premul(const SkISize& size)

Parameters

size	incomplete

Return Value

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Example

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MakeA8

static SkImageInfo MakeA8(int width, int height)

Parameters

width	incomplete
height	incomplete

Return Value

incomplete

Example

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MakeUnknown

static SkImageInfo MakeUnknown(int width, int height)

Parameters

width	incomplete
height	incomplete

Return Value

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Example

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static SkImageInfo MakeUnknown()

Return Value

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Example

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Property

name	description
alphaType	incomplete
bounds	incomplete
bytesPerPixel	incomplete
colorSpace	incomplete
colorType	incomplete
dimensions	incomplete
gammaCloseToSRGB	incomplete
height	incomplete
isEmpty	incomplete
isOpaque	incomplete
minRowBytes	incomplete
minRowBytes64	incomplete
refColorSpace	incomplete
shiftPerPixel	incomplete
width	incomplete

width

int width() const

Return Value

incomplete

Example

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height

int height() const

Return Value

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Example

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colorType

SkColorType colorType() const

Return Value

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Example

See Also

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alphaType

SkAlphaType alphaType() const

Return Value

incomplete

Example

See Also

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colorSpace

SkColorSpace* colorSpace() const

Return Value

incomplete

Example

See Also

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refColorSpace

sk_sp<SkColorSpace> refColorSpace() const

Return Value

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Example

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isEmpty

bool isEmpty() const

Return Value

incomplete

Example

See Also

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isOpaque

bool isOpaque() const

Return Value

incomplete

Example

See Also

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dimensions

SkISize dimensions() const

Return Value

incomplete

Example

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bounds

SkIRect bounds() const

Return Value

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Example

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gammaCloseToSRGB

bool gammaCloseToSRGB() const

Return Value

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Example

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makeWH

SkImageInfo makeWH(int newWidth, int newHeight) const

Creates Image Info with the same Color Type and Alpha Type as this info, but with the specified width and height.

Parameters

newWidth	incomplete
newHeight	incomplete

Return Value

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Example

See Also

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makeAlphaType

SkImageInfo makeAlphaType(SkAlphaType newAlphaType) const

Parameters

newAlphaType

incomplete

Return Value

incomplete

Example

See Also

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makeColorType

SkImageInfo makeColorType(SkColorType newColorType) const

Parameters

newColorType

incomplete

Return Value

incomplete

Example

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makeColorSpace

SkImageInfo makeColorSpace(sk_sp<SkColorSpace> cs) const

Parameters

cs	incomplete

Return Value

incomplete

Example

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bytesPerPixel

int bytesPerPixel() const

Return Value

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Example

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shiftPerPixel

int shiftPerPixel() const

Return Value

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Example

See Also

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minRowBytes64

uint64_t minRowBytes64() const

Return Value

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Example

See Also

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minRowBytes

size_t minRowBytes() const

Return Value

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Example

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computeOffset

size_t computeOffset(int x, int y, size_t rowBytes) const

Parameters

x	incomplete
y	incomplete
rowBytes	incomplete

Return Value

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Example

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Operator

name	description
operator!=(const SkImageInfo& other) const	incomplete
operator==(const SkImageInfo& other) const	incomplete

operator==

bool operator==(const SkImageInfo& other) _const

Parameters

other

incomplete

Return Value

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Example

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operator!=

bool operator!=(const SkImageInfo& other) _const

Parameters

other

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Return Value

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Example

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unflatten

void unflatten(SkReadBuffer& buffer)

Parameters

buffer

incomplete

Example

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flatten

void flatten(SkWriteBuffer& buffer) const

Parameters

buffer

incomplete

Example

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computeByteSize

size_t computeByteSize(size_t rowBytes) const

Returns the size (in bytes) of the image buffer that this info needs, given the specified rowBytes. The rowBytes must be >= this->minRowBytes. if (height == 0) { return 0; } else { return (height - 1) * rowBytes + width * bytes_per_pixel.

If the calculation overflows this returns SK MaxSizeT.

Parameters

rowBytes

incomplete

Return Value

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Example

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computeMinByteSize

size_t computeMinByteSize() const

Returns the minimum size (in bytes) of the image buffer that this info needs. If the calculation overflows, or if the height is 0, this returns 0.

Return Value

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Example

See Also

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ByteSizeOverflowed

static bool ByteSizeOverflowed(size_t byteSize)

Returns true if the result of computeByteSize (or computeMinByteSize) overflowed

Parameters

byteSize

incomplete

Return Value

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Example

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validRowBytes

bool validRowBytes(size_t rowBytes) const

Parameters

rowBytes

incomplete

Return Value

incomplete

Example

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reset

void reset()

Example

See Also

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Utility

name	description
ByteSizeOverflowed	incomplete
computeByteSize	incomplete
computeMinByteSize	incomplete
computeOffset	incomplete
flatten	incomplete
unflatten	incomplete
validRowBytes	incomplete
validate	incomplete

validate

void validate() const

Example

See Also

incomplete

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