skia2/include/core/SkImageInfo.h

/*
 * Copyright 2013 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkImageInfo_DEFINED
#define SkImageInfo_DEFINED

#include "SkColorSpace.h"
#include "SkMath.h"
#include "SkRect.h"
#include "SkSize.h"
#include "../private/SkTFitsIn.h"

class SkReadBuffer;
class SkWriteBuffer;

/** \enum SkImageInfo::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:In practice alpha is encoded in two or more bits, where 1.0 equals all bits set.

    RGB may have color alpha included in each component value; the stored
    value is the original RGB multiplied by color alpha. Premultiplied color
    components improve performance.
*/
enum SkAlphaType {
    kUnknown_SkAlphaType,                          //!< SkAlphaType is uninitialized.

    /** Pixels are opaque. The SkColorType must have no explicit alpha
        component, or all alpha components must be set to their maximum value.
    */
    kOpaque_SkAlphaType,

    /** Pixels have alpha premultiplied into color components.
        SkSurface pixels must be premultiplied.
    */
    kPremul_SkAlphaType,

    /** 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 SkImage pixels, but not for
        SkSurface pixels.
    */
    kUnpremul_SkAlphaType,

    /** 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 SkImage pixels, but not for
        SkSurface pixels.
    */
    kLastEnum_SkAlphaType = kUnpremul_SkAlphaType,
};

/** Returns true if SkAlphaType equals kOpaque_SkAlphaType. kOpaque_SkAlphaType is a
    hint that the SkColorType is opaque, or that all color alpha values are set to
    their 1.0 equivalent. If SkAlphaType is kOpaque_SkAlphaType, and SkColorType is not
    opaque, then the result of drawing any pixel with a color alpha value less than
    1.0 is undefined.

    @param at  one of:
               kUnknown_SkAlphaType, kOpaque_SkAlphaType, kPremul_SkAlphaType,
               kUnpremul_SkAlphaType
    @return    true if at equals kOpaque_SkAlphaType
*/
static inline bool SkAlphaTypeIsOpaque(SkAlphaType at) {
    return kOpaque_SkAlphaType == at;
}

///////////////////////////////////////////////////////////////////////////////

/** Temporary macro that allows us to add new color types without breaking Chrome compile. */
#define SK_EXTENDED_COLOR_TYPES

/** \enum SkImageInfo::SkColorType
    Describes how pixel bits encode color. A pixel may be an alpha mask, a
    gray level, RGB, or ARGB.

    kN32_SkColorType selects the native 32-bit ARGB format. On Little_Endian
    processors, pixels containing 8-bit ARGB components pack into 32-bit
    kBGRA_8888_SkColorType. On Big_Endian processors, pixels pack into 32-bit
    kRGBA_8888_SkColorType.
*/
enum SkColorType {
    /** SkColorType is uninitialized; encoding format and size is unknown. */
    kUnknown_SkColorType,

    /** Encodes color alpha as alpha 8 pixel in an 8-bit byte. */
    kAlpha_8_SkColorType,

    /** Encodes RGB as bgr 565 pixel in a 16-bit word. */
    kRGB_565_SkColorType,

    /** Encodes ARGB as abgr 4444 pixel in a 16-bit word. */
    kARGB_4444_SkColorType,

    /** Encodes ARGB as rgba 8888 pixel in a 32-bit word. */
    kRGBA_8888_SkColorType,

    /** Encodes RGB as rgb 888x pixel in a 32-bit word. */
    kRGB_888x_SkColorType,

    /** Encodes ARGB as bgra 8888 pixel in a 32-bit word. */
    kBGRA_8888_SkColorType,

    /** Encodes ARGB as rgba 1010102 pixel in a 32-bit word. */
    kRGBA_1010102_SkColorType,

    /** Encodes RGB as rgb 101010x pixel in a 32-bit word. */
    kRGB_101010x_SkColorType,

    /** Encodes color gray as gray 8 in an 8-bit byte. */
    kGray_8_SkColorType,

    /** Encodes ARGB as rgba f16 in a 64-bit word. */
    kRGBA_F16_SkColorType,

    /** Encodes ARGB as rgba f16 in a 64-bit word. */
    kLastEnum_SkColorType     = kRGBA_F16_SkColorType,

#if SK_PMCOLOR_BYTE_ORDER(B,G,R,A)
    /** Encodes ARGB as either rgba 8888 or bgra 8888, whichever
        is native to the platform.
    */
    kN32_SkColorType          = kBGRA_8888_SkColorType,

#elif SK_PMCOLOR_BYTE_ORDER(R,G,B,A)

    /** Encodes ARGB as either rgba 8888 or bgra 8888, whichever
        is native to the platform.
    */
    kN32_SkColorType          = kRGBA_8888_SkColorType,

#else
    #error "SK_*32_SHIFT values must correspond to BGRA or RGBA byte order"
#endif
};

/** Returns the number of bytes required to store a pixel, including unused padding.
    Returns zero if ct is kUnknown_SkColorType or invalid.

    @param ct  one of:
               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
    @return    bytes per pixel
*/
SK_API int SkColorTypeBytesPerPixel(SkColorType ct);

/** Returns true if SkColorType always decodes color alpha to 1.0, making the pixel
    fully opaque. If true, SkColorType does not reserve bits to encode color alpha.

    @param ct  one of:
               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
    @return    true if color alpha is always set to 1.0
*/
SK_API bool SkColorTypeIsAlwaysOpaque(SkColorType ct);

/** Returns true if canonical can be set to a valid SkAlphaType for colorType. If
    there is more than one valid canonical SkAlphaType, set to alphaType, if valid.
    If true is returned and canonical is not nullptr, store valid SkAlphaType.

    Returns false only if alphaType is kUnknown_SkAlphaType, color type is not
    kUnknown_SkColorType, and SkColorType is not always opaque. If false is returned,
    canonical is ignored.

    For kUnknown_SkColorType: set canonical to kUnknown_SkAlphaType and return true.
    For kAlpha_8_SkColorType: set canonical to kPremul_SkAlphaType or
    kOpaque_SkAlphaType and return true if alphaType is not kUnknown_SkAlphaType.
    For kRGB_565_SkColorType, kRGB_888x_SkColorType, kRGB_101010x_SkColorType, and
    kGray_8_SkColorType: set canonical to kOpaque_SkAlphaType and return true.
    For kARGB_4444_SkColorType, kRGBA_8888_SkColorType, kBGRA_8888_SkColorType,
    kRGBA_1010102_SkColorType, and kRGBA_F16_SkColorType: set canonical to alphaType
    and return true if alphaType is not kUnknown_SkAlphaType.

    @param colorType  one of:
                      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
    @param alphaType  one of:
                      kUnknown_SkAlphaType, kOpaque_SkAlphaType, kPremul_SkAlphaType,
                      kUnpremul_SkAlphaType
    @param canonical  storage for SkAlphaType
    @return           true if valid SkAlphaType can be associated with colorType
*/
SK_API bool SkColorTypeValidateAlphaType(SkColorType colorType, SkAlphaType alphaType,
                                         SkAlphaType* canonical = nullptr);

/** \enum SkImageInfo::SkYUVColorSpace
    Describes color range of YUV pixels. The color mapping from YUV to RGB varies
    depending on the source. YUV pixels may be generated by JPEG images, standard
    video streams, or high definition video streams. Each has its own mapping from
    YUV and RGB.

    JPEG YUV values encode the full range of 0 to 255 for all three components.
    Video YUV values range from 16 to 235 for all three components. Details of
    encoding and conversion to RGB are described in YCbCr color space.
*/
enum SkYUVColorSpace {
    /** Describes standard JPEG color space; */
    kJPEG_SkYUVColorSpace,

    /** Describes standard used by SDTV; */
    kRec601_SkYUVColorSpace,

    /** Describes standard used by HDTV; */
    kRec709_SkYUVColorSpace,

    /** Describes standard used by HDTV; */
    kLastEnum_SkYUVColorSpace = kRec709_SkYUVColorSpace,
};

/** \struct SkImageInfo
    Describes pixel dimensions and encoding. SkBitmap, SkImage, PixMap, and SkSurface
    can be created from SkImageInfo. SkImageInfo can be retrieved from SkBitmap and
    SkPixmap, but not from SkImage and SkSurface. For example, SkImage and SkSurface
    implementations may defer pixel depth, so may not completely specify SkImageInfo.

    SkImageInfo contains dimensions, the pixel integral width and height. It encodes
    how pixel bits describe color alpha, transparency; color components red, blue,
    and green; and SkColorSpace, the range and linearity of colors.
*/
struct SK_API SkImageInfo {
public:

    /** Creates an empty SkImageInfo with kUnknown_SkColorType, kUnknown_SkAlphaType,
        a width and height of zero, and no SkColorSpace.

        @return  empty SkImageInfo
    */
    SkImageInfo()
        : fColorSpace(nullptr)
        , fWidth(0)
        , fHeight(0)
        , fColorType(kUnknown_SkColorType)
        , fAlphaType(kUnknown_SkAlphaType)
    {}

    /** Creates SkImageInfo from integral dimensions width and height, SkColorType ct,
        SkAlphaType at, and optionally SkColorSpace cs.

        If SkColorSpace cs is nullptr and SkImageInfo is part of drawing source: SkColorSpace
        defaults to sRGB, mapping into SkSurface SkColorSpace.

        Parameters are not validated to see if their values are legal, or that the
        combination is supported.

        @param width   pixel column count; must be zero or greater
        @param height  pixel row count; must be zero or greater
        @param ct      one of:
                       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
        @param at      one of:
                       kUnknown_SkAlphaType, kOpaque_SkAlphaType, kPremul_SkAlphaType,
                       kUnpremul_SkAlphaType
        @param cs      range of colors; may be nullptr
        @return        created SkImageInfo
    */
    static SkImageInfo Make(int width, int height, SkColorType ct, SkAlphaType at,
                            sk_sp<SkColorSpace> cs = nullptr) {
        return SkImageInfo(width, height, ct, at, std::move(cs));
    }

    /** Creates SkImageInfo from integral dimensions width and height, kN32_SkColorType,
        SkAlphaType at, and optionally SkColorSpace cs. kN32_SkColorType will equal either
        kBGRA_8888_SkColorType or kRGBA_8888_SkColorType, whichever is optimal.

        If SkColorSpace cs is nullptr and SkImageInfo is part of drawing source: SkColorSpace
        defaults to sRGB, mapping into SkSurface SkColorSpace.

        Parameters are not validated to see if their values are legal, or that the
        combination is supported.

        @param width   pixel column count; must be zero or greater
        @param height  pixel row count; must be zero or greater
        @param at      one of:
                       kUnknown_SkAlphaType, kOpaque_SkAlphaType, kPremul_SkAlphaType,
                       kUnpremul_SkAlphaType
        @param cs      range of colors; may be nullptr
        @return        created SkImageInfo
    */
    static SkImageInfo MakeN32(int width, int height, SkAlphaType at,
                               sk_sp<SkColorSpace> cs = nullptr) {
        return Make(width, height, kN32_SkColorType, at, cs);
    }

    /** Creates SkImageInfo from integral dimensions width and height, kN32_SkColorType,
        SkAlphaType at, with sRGB SkColorSpace.

        Parameters are not validated to see if their values are legal, or that the
        combination is supported.

        @param width   pixel column count; must be zero or greater
        @param height  pixel row count; must be zero or greater
        @param at      one of:
                       kUnknown_SkAlphaType, kOpaque_SkAlphaType, kPremul_SkAlphaType,
                       kUnpremul_SkAlphaType
        @return        created SkImageInfo
    */
    static SkImageInfo MakeS32(int width, int height, SkAlphaType at);

    /** Creates SkImageInfo from integral dimensions width and height, kN32_SkColorType,
        kPremul_SkAlphaType, with optional SkColorSpace.

        If SkColorSpace cs is nullptr and SkImageInfo is part of drawing source: SkColorSpace
        defaults to sRGB, mapping into SkSurface SkColorSpace.

        Parameters are not validated to see if their values are legal, or that the
        combination is supported.

        @param width   pixel column count; must be zero or greater
        @param height  pixel row count; must be zero or greater
        @param cs      range of colors; may be nullptr
        @return        created SkImageInfo
    */
    static SkImageInfo MakeN32Premul(int width, int height, sk_sp<SkColorSpace> cs = nullptr) {
        return Make(width, height, kN32_SkColorType, kPremul_SkAlphaType, cs);
    }

    /** Creates SkImageInfo from integral dimensions width and height, kN32_SkColorType,
        kPremul_SkAlphaType, with SkColorSpace set to nullptr.

        If SkImageInfo is part of drawing source: SkColorSpace defaults to sRGB, mapping
        into SkSurface SkColorSpace.

        Parameters are not validated to see if their values are legal, or that the
        combination is supported.

        @param size  width and height, each must be zero or greater
        @return      created SkImageInfo
    */
    static SkImageInfo MakeN32Premul(const SkISize& size) {
        return MakeN32Premul(size.width(), size.height());
    }

    /** Creates SkImageInfo from integral dimensions width and height, kAlpha_8_SkColorType,
        kPremul_SkAlphaType, with SkColorSpace set to nullptr.

        @param width   pixel column count; must be zero or greater
        @param height  pixel row count; must be zero or greater
        @return        created SkImageInfo
    */
    static SkImageInfo MakeA8(int width, int height) {
        return Make(width, height, kAlpha_8_SkColorType, kPremul_SkAlphaType, nullptr);
    }

    /** Creates SkImageInfo from integral dimensions width and height, kUnknown_SkColorType,
        kUnknown_SkAlphaType, with SkColorSpace set to nullptr.

        Returned SkImageInfo as part of source does not draw, and as part of destination
        can not be drawn to.

        @param width   pixel column count; must be zero or greater
        @param height  pixel row count; must be zero or greater
        @return        created SkImageInfo
    */
    static SkImageInfo MakeUnknown(int width, int height) {
        return Make(width, height, kUnknown_SkColorType, kUnknown_SkAlphaType, nullptr);
    }

    /** Creates SkImageInfo from integral dimensions width and height set to zero,
        kUnknown_SkColorType, kUnknown_SkAlphaType, with SkColorSpace set to nullptr.

        Returned SkImageInfo as part of source does not draw, and as part of destination
        can not be drawn to.

        @return  created SkImageInfo
    */
    static SkImageInfo MakeUnknown() {
        return MakeUnknown(0, 0);
    }

    /** Returns pixel count in each row.

        @return  pixel width
    */
    int width() const { return fWidth; }

    /** Returns pixel row count.

        @return  pixel height
    */
    int height() const { return fHeight; }

    /** Returns SkColorType, one of:
        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.

        @return  SkColorType
    */
    SkColorType colorType() const { return fColorType; }

    /** Returns SkAlphaType, one of:
        kUnknown_SkAlphaType, kOpaque_SkAlphaType, kPremul_SkAlphaType,
        kUnpremul_SkAlphaType.

        @return  SkAlphaType
    */
    SkAlphaType alphaType() const { return fAlphaType; }

    /** Returns SkColorSpace, the range of colors. The reference count of
        SkColorSpace is unchanged. The returned SkColorSpace is immutable.

        @return  SkColorSpace, or nullptr
    */
    SkColorSpace* colorSpace() const { return fColorSpace.get(); }

    /** Returns smart pointer to SkColorSpace, the range of colors. The smart pointer
        tracks the number of objects sharing this SkColorSpace reference so the memory
        is released when the owners destruct.

        The returned SkColorSpace is immutable.

        @return  SkColorSpace wrapped in a smart pointer
    */
    sk_sp<SkColorSpace> refColorSpace() const { return fColorSpace; }

    /** Returns if SkImageInfo describes an empty area of pixels by checking if either
        width or height is zero or smaller.

        @return  true if either dimension is zero or smaller
    */
    bool isEmpty() const { return fWidth <= 0 || fHeight <= 0; }

    /** Returns true if SkAlphaType is set to hint that all pixels are opaque; their
        color alpha value is implicitly or explicitly 1.0. If true, and all pixels are
        not opaque, Skia may draw incorrectly.

        Does not check if SkColorType allows alpha, or if any pixel value has
        transparency.

        @return  true if SkAlphaType is kOpaque_SkAlphaType
    */
    bool isOpaque() const {
        return SkAlphaTypeIsOpaque(fAlphaType);
    }

    /** Returns SkISize { width(), height() }.

        @return  integral size of width() and height()
    */
    SkISize dimensions() const { return SkISize::Make(fWidth, fHeight); }

    /** Returns SkIRect { 0, 0, width(), height() }.

        @return  integral rectangle from origin to width() and height()
    */
    SkIRect bounds() const { return SkIRect::MakeWH(fWidth, fHeight); }

    /** Returns true if associated SkColorSpace is not nullptr, and SkColorSpace gamma
        is approximately the same as sRGB.
        This includes the

        @return  true if SkColorSpace gamma is approximately the same as sRGB
    */
    bool gammaCloseToSRGB() const {
        return fColorSpace && fColorSpace->gammaCloseToSRGB();
    }

    /** Creates SkImageInfo with the same SkColorType, SkColorSpace, and SkAlphaType,
        with dimensions set to width and height.

        @param newWidth   pixel column count; must be zero or greater
        @param newHeight  pixel row count; must be zero or greater
        @return           created SkImageInfo
    */
    SkImageInfo makeWH(int newWidth, int newHeight) const {
        return Make(newWidth, newHeight, fColorType, fAlphaType, fColorSpace);
    }

    /** Creates SkImageInfo with same SkColorType, SkColorSpace, width, and height,
        with SkAlphaType set to newAlphaType.

        Created SkImageInfo contains newAlphaType even if it is incompatible with
        SkColorType, in which case SkAlphaType in SkImageInfo is ignored.

        @param newAlphaType  one of:
                             kUnknown_SkAlphaType, kOpaque_SkAlphaType, kPremul_SkAlphaType,
                             kUnpremul_SkAlphaType
        @return              created SkImageInfo
    */
    SkImageInfo makeAlphaType(SkAlphaType newAlphaType) const {
        return Make(fWidth, fHeight, fColorType, newAlphaType, fColorSpace);
    }

    /** Creates SkImageInfo with same SkAlphaType, SkColorSpace, width, and height,
        with SkColorType set to newColorType.

        @param newColorType  one of:
                             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
        @return              created SkImageInfo
    */
    SkImageInfo makeColorType(SkColorType newColorType) const {
        return Make(fWidth, fHeight, newColorType, fAlphaType, fColorSpace);
    }

    /** Creates SkImageInfo with same SkAlphaType, SkColorType, width, and height,
        with SkColorSpace set to cs.

        @param cs  range of colors; may be nullptr
        @return    created SkImageInfo
    */
    SkImageInfo makeColorSpace(sk_sp<SkColorSpace> cs) const {
        return Make(fWidth, fHeight, fColorType, fAlphaType, std::move(cs));
    }

    /** Returns number of bytes per pixel required by SkColorType.
        Returns zero if colorType( is kUnknown_SkColorType.

        @return  bytes in pixel
    */
    int bytesPerPixel() const;

    /** Returns bit shift converting row bytes to row pixels.
        Returns zero for kUnknown_SkColorType.

        @return  one of: 0, 1, 2, 3; left shift to convert pixels to bytes
    */
    int shiftPerPixel() const;

    /** Returns minimum bytes per row, computed from pixel width() and SkColorType, which
        specifies bytesPerPixel(). SkBitmap maximum value for row bytes must be representable
        as a positive value in a 32-bit signed integer.

        @return  width() times bytesPerPixel() as unsigned 64-bit integer
    */
    uint64_t minRowBytes64() const {
        return sk_64_mul(fWidth, this->bytesPerPixel());
    }

    /** Returns minimum bytes per row, computed from pixel width() and SkColorType, which
        specifies bytesPerPixel(). SkBitmap maximum value for row bytes must be representable
        as a positive value in a 32-bit signed integer.

        @return  width() times bytesPerPixel() as signed 32-bit integer
    */
    size_t minRowBytes() const {
        uint64_t minRowBytes = this->minRowBytes64();
        if (!SkTFitsIn<int32_t>(minRowBytes)) {
            return 0;
        }
        return SkTo<int32_t>(minRowBytes);
    }

    /** Returns byte offset of pixel from pixel base address.

        Asserts in debug build if x or y is outside of bounds. Does not assert if
        rowBytes is smaller than minRowBytes(), even though result may be incorrect.

        @param x         column index, zero or greater, and less than width()
        @param y         row index, zero or greater, and less than height()
        @param rowBytes  size of pixel row or larger
        @return          offset within pixel array
    */
    size_t computeOffset(int x, int y, size_t rowBytes) const;

    /** Compares SkImageInfo with other, and returns true if width, height, SkColorType,
        SkAlphaType, and SkColorSpace are equivalent.

        @param other  SkImageInfo to compare
        @return       true if SkImageInfo equals other
    */
    bool operator==(const SkImageInfo& other) const {
        return fWidth == other.fWidth && fHeight == other.fHeight &&
               fColorType == other.fColorType && fAlphaType == other.fAlphaType &&
               SkColorSpace::Equals(fColorSpace.get(), other.fColorSpace.get());
    }

    /** Compares SkImageInfo with other, and returns true if width, height, SkColorType,
        SkAlphaType, and SkColorSpace are equivalent.

        @param other  SkImageInfo to compare
        @return       true if SkImageInfo is not equal to other
    */
    bool operator!=(const SkImageInfo& other) const {
        return !(*this == other);
    }

    /** Returns storage required by pixel array, given SkImageInfo dimensions, SkColorType,
        and rowBytes. rowBytes is assumed to be at least as large as minRowBytes().

        Returns zero if height is zero.
        Returns SK_MaxSizeT if answer exceeds the range of size_t.

        @param rowBytes  size of pixel row or larger
        @return          memory required by pixel buffer
    */
    size_t computeByteSize(size_t rowBytes) const;

    /** Returns storage required by pixel array, given SkImageInfo dimensions, and
        SkColorType. Uses minRowBytes() to compute bytes for pixel row.

        Returns zero if height is zero.
        Returns SK_MaxSizeT if answer exceeds the range of size_t.

        @return  least memory required by pixel buffer
    */
    size_t computeMinByteSize() const {
        return this->computeByteSize(this->minRowBytes());
    }

    /** Returns true if byteSize equals SK_MaxSizeT. computeByteSize() and
        computeMinByteSize() return SK_MaxSizeT if size_t can not hold buffer size.

        @param byteSize  result of computeByteSize() or computeMinByteSize()
        @return          true if computeByteSize() or computeMinByteSize() result exceeds size_t
    */
    static bool ByteSizeOverflowed(size_t byteSize) {
        return SK_MaxSizeT == byteSize;
    }

    /** Returns true if rowBytes is smaller than width times pixel size.

        @param rowBytes  size of pixel row or larger
        @return          true if rowBytes is large enough to contain pixel row
    */
    bool validRowBytes(size_t rowBytes) const {
        uint64_t minRB = sk_64_mul(fWidth, this->bytesPerPixel());
        return rowBytes >= minRB;
    }

    /** Creates an empty SkImageInfo with kUnknown_SkColorType, kUnknown_SkAlphaType,
        a width and height of zero, and no SkColorSpace.
    */
    void reset() {
        fColorSpace = nullptr;
        fWidth = 0;
        fHeight = 0;
        fColorType = kUnknown_SkColorType;
        fAlphaType = kUnknown_SkAlphaType;
    }

    /** Asserts if internal values are illegal or inconsistent. Only available if
        SK_DEBUG is defined at compile time.
    */
    SkDEBUGCODE(void validate() const;)

private:
    sk_sp<SkColorSpace> fColorSpace;
    int                 fWidth;
    int                 fHeight;
    SkColorType         fColorType;
    SkAlphaType         fAlphaType;

    SkImageInfo(int width, int height, SkColorType ct, SkAlphaType at, sk_sp<SkColorSpace> cs)
        : fColorSpace(std::move(cs))
        , fWidth(width)
        , fHeight(height)
        , fColorType(ct)
        , fAlphaType(at)
    {}
};

#endif