src/codec/SkCodecPriv.h

/*
 * Copyright 2015 The Android Open Source Project
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkCodecPriv_DEFINED
#define SkCodecPriv_DEFINED

#include "SkColorTable.h"
#include "SkImageInfo.h"
#include "SkSwizzler.h"
#include "SkTypes.h"
#include "SkUtils.h"

/*
 *
 * Helper routine for alpha result codes
 *
 */
#define INIT_RESULT_ALPHA                       \
    uint8_t zeroAlpha = 0;                      \
    uint8_t maxAlpha = 0xFF;

#define UPDATE_RESULT_ALPHA(alpha)              \
    zeroAlpha |= (alpha);                       \
    maxAlpha  &= (alpha);

#define COMPUTE_RESULT_ALPHA                    \
    SkSwizzler::GetResult(zeroAlpha, maxAlpha);

/*
 * returns a scaled dimension based on the original dimension and the sampleSize
 * NOTE: we round down here for scaled dimension to match the behavior of SkImageDecoder
 */
static int get_scaled_dimension(int srcDimension, int sampleSize) {
    if (sampleSize > srcDimension) {
        return 1;
    }
    return srcDimension / sampleSize;
}

/*
 * Returns the first coordinate that we will keep during a scaled decode.
 * The output can be interpreted as an x-coordinate or a y-coordinate.
 *
 * This does not need to be called and is not called when sampleFactor == 1.
 */
static int get_start_coord(int sampleFactor) { return sampleFactor / 2; };

/*
 * Given a coordinate in the original image, this returns the corresponding
 * coordinate in the scaled image.  This function is meaningless if
 * IsCoordNecessary returns false.
 * The output can be interpreted as an x-coordinate or a y-coordinate.
 *
 * This does not need to be called and is not called when sampleFactor == 1.
 */
static int get_dst_coord(int srcCoord, int sampleFactor) { return srcCoord / sampleFactor; };

/*
 * When scaling, we will discard certain y-coordinates (rows) and
 * x-coordinates (columns).  This function returns true if we should keep the
 * coordinate and false otherwise.
 * The inputs may be x-coordinates or y-coordinates.
 *
 * This does not need to be called and is not called when sampleFactor == 1.
 */
static bool is_coord_necessary(int srcCoord, int sampleFactor, int scaledDim) {
    // Get the first coordinate that we want to keep
    int startCoord = get_start_coord(sampleFactor);

    // Return false on edge cases
    if (srcCoord < startCoord || get_dst_coord(srcCoord, sampleFactor) >= scaledDim) {
        return false;
    }

    // Every sampleFactor rows are necessary
    return ((srcCoord - startCoord) % sampleFactor) == 0;
}

static inline bool valid_alpha(SkAlphaType dstAlpha, SkAlphaType srcAlpha) {
    // Check for supported alpha types
    if (srcAlpha != dstAlpha) {
        if (kOpaque_SkAlphaType == srcAlpha) {
            // If the source is opaque, we must decode to opaque
            return false;
        }

        // The source is not opaque
        switch (dstAlpha) {
            case kPremul_SkAlphaType:
            case kUnpremul_SkAlphaType:
                // The source is not opaque, so either of these is okay
                break;
            default:
                // We cannot decode a non-opaque image to opaque (or unknown)
                return false;
        }
    }
    return true;
}

/*
 * Most of our codecs support the same conversions:
 * - profileType must be the same
 * - opaque only to opaque (and 565 only if opaque)
 * - premul to unpremul and vice versa
 * - always support N32
 * - otherwise match the src color type
 */
static bool conversion_possible(const SkImageInfo& dst, const SkImageInfo& src) {
    if (dst.profileType() != src.profileType()) {
        return false;
    }

    // Ensure the alpha type is valid
    if (!valid_alpha(dst.alphaType(), src.alphaType())) {
        return false;
    }

    // Check for supported color types
    switch (dst.colorType()) {
        case kN32_SkColorType:
            return true;
        case kRGB_565_SkColorType:
            return src.alphaType() == kOpaque_SkAlphaType;
        default:
            return dst.colorType() == src.colorType();
    }
}

/*
 * If there is a color table, get a pointer to the colors, otherwise return nullptr
 */
static const SkPMColor* get_color_ptr(SkColorTable* colorTable) {
     return nullptr != colorTable ? colorTable->readColors() : nullptr;
}

/*
 *
 * Copy the codec color table back to the client when kIndex8 color type is requested
 */
static inline void copy_color_table(const SkImageInfo& dstInfo, SkColorTable* colorTable,
        SkPMColor* inputColorPtr, int* inputColorCount) {
    if (kIndex_8_SkColorType == dstInfo.colorType()) {
        SkASSERT(nullptr != inputColorPtr);
        SkASSERT(nullptr != inputColorCount);
        SkASSERT(nullptr != colorTable);
        memcpy(inputColorPtr, colorTable->readColors(), *inputColorCount * sizeof(SkPMColor));
    }
}

/*
 * Compute row bytes for an image using pixels per byte
 */
static inline size_t compute_row_bytes_ppb(int width, uint32_t pixelsPerByte) {
    return (width + pixelsPerByte - 1) / pixelsPerByte;
}

/*
 * Compute row bytes for an image using bytes per pixel
 */
static inline size_t compute_row_bytes_bpp(int width, uint32_t bytesPerPixel) {
    return width * bytesPerPixel;
}

/*
 * Compute row bytes for an image
 */
static inline size_t compute_row_bytes(int width, uint32_t bitsPerPixel) {
    if (bitsPerPixel < 16) {
        SkASSERT(0 == 8 % bitsPerPixel);
        const uint32_t pixelsPerByte = 8 / bitsPerPixel;
        return compute_row_bytes_ppb(width, pixelsPerByte);
    } else {
        SkASSERT(0 == bitsPerPixel % 8);
        const uint32_t bytesPerPixel = bitsPerPixel / 8;
        return compute_row_bytes_bpp(width, bytesPerPixel);
    }
}

/*
 * On incomplete images, get the color to fill with
 */
static inline SkPMColor get_fill_color_or_index(SkAlphaType alphaType) {
    // This condition works properly for all supported output color types.
    // kIndex8: The low 8-bits of both possible return values is 0, which is
    //          our desired default index.
    // kGray8:  The low 8-bits of both possible return values is 0, which is
    //          black, our desired fill value.
    // kRGB565: The low 16-bits of both possible return values is 0, which is
    //          black, our desired fill value.
    // kN32:    Return black for opaque images and transparent for non-opaque
    //          images.
    return kOpaque_SkAlphaType == alphaType ?
            SK_ColorBLACK : SK_ColorTRANSPARENT;
}

/*
 * Get a byte from a buffer
 * This method is unsafe, the caller is responsible for performing a check
 */
static inline uint8_t get_byte(uint8_t* buffer, uint32_t i) {
    return buffer[i];
}

/*
 * Get a short from a buffer
 * This method is unsafe, the caller is responsible for performing a check
 */
static inline uint16_t get_short(uint8_t* buffer, uint32_t i) {
    uint16_t result;
    memcpy(&result, &(buffer[i]), 2);
#ifdef SK_CPU_BENDIAN
    return SkEndianSwap16(result);
#else
    return result;
#endif
}

/*
 * Get an int from a buffer
 * This method is unsafe, the caller is responsible for performing a check
 */
static inline uint32_t get_int(uint8_t* buffer, uint32_t i) {
    uint32_t result;
    memcpy(&result, &(buffer[i]), 4);
#ifdef SK_CPU_BENDIAN
    return SkEndianSwap32(result);
#else
    return result;
#endif
}

#ifdef SK_PRINT_CODEC_MESSAGES
    #define SkCodecPrintf SkDebugf
#else
    #define SkCodecPrintf(...)
#endif

#endif // SkCodecPriv_DEFINED