src/codec/SkSwizzler.h

/*
 * Copyright 2015 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */

#ifndef SkSwizzler_DEFINED
#define SkSwizzler_DEFINED

#include "SkCodec.h"
#include "SkColor.h"
#include "SkImageInfo.h"

class SkSwizzler : public SkNoncopyable {
public:
    /**
     *  Enum describing the config of the source data.
     */
    enum SrcConfig {
        kUnknown,  // Invalid type.
        kBit,      // A single bit to distinguish between white and black
        kGray,
        kIndex1,
        kIndex2,
        kIndex4,
        kIndex,
        kRGB,
        kBGR,
        kRGBX,
        kBGRX,
        kRGBA,
        kBGRA,
        kRGB_565,
    };

    /*
     *
     * Result code for the alpha components of a row.
     *
     */
    typedef uint16_t ResultAlpha;
    static const ResultAlpha kOpaque_ResultAlpha = 0xFFFF;
    static const ResultAlpha kTransparent_ResultAlpha = 0x0000;

    /*
     *
     * Checks if the result of decoding a row indicates that the row was
     * transparent.
     *
     */
    static bool IsTransparent(ResultAlpha r) {
        return kTransparent_ResultAlpha == r;
    }

    /*
     *
     * Checks if the result of decoding a row indicates that the row was
     * opaque.
     *
     */
    static bool IsOpaque(ResultAlpha r) {
        return kOpaque_ResultAlpha == r;
    }

    /*
     *
     * Constructs the proper result code based on accumulated alpha masks
     *
     */
    static ResultAlpha GetResult(uint8_t zeroAlpha, uint8_t maxAlpha);

    /*
     *
     * Returns bits per pixel for source config
     *
     */
    static int BitsPerPixel(SrcConfig sc) {
        switch (sc) {
            case kBit:
            case kIndex1:
                return 1;
            case kIndex2:
                return 2;
            case kIndex4:
                return 4;
            case kGray:
            case kIndex:
                return 8;
            case kRGB_565:
                return 16;
            case kRGB:
            case kBGR:
                return 24;
            case kRGBX:
            case kRGBA:
            case kBGRX:
            case kBGRA:
                return 32;
            default:
                SkASSERT(false);
                return 0;
        }
    }

    /*
     *
     * Returns bytes per pixel for source config
     * Raises an error if each pixel is not stored in an even number of bytes
     *
     */
    static int BytesPerPixel(SrcConfig sc) {
        SkASSERT(SkIsAlign8(BitsPerPixel(sc)));
        return BitsPerPixel(sc) >> 3;
    }

    /**
     *  Create a new SkSwizzler.
     *  @param SrcConfig Description of the format of the source.
     *  @param dstInfo describes the destination.
     *  @param ZeroInitialized Whether dst is zero-initialized. The
                               implementation may choose to skip writing zeroes
     *                         if set to kYes_ZeroInitialized.
     *  @param srcInfo is the info of the source. Used to calculate the width samplesize.
     *                  Width sampling is supported by the swizzler, by skipping pixels when 
                        swizzling the row. Height sampling is not supported by the swizzler, 
                        but is implemented in SkScaledCodec.
                        Sampling in Y can be done by a client with a scanline decoder, 
                        but sampling in X allows the swizzler to skip swizzling pixels and
                        reading from and writing to memory.
     *  @return A new SkSwizzler or nullptr on failure.
     */
    static SkSwizzler* CreateSwizzler(SrcConfig, const SkPMColor* ctable,
                                      const SkImageInfo& dstInfo, SkCodec::ZeroInitialized, 
                                      const SkImageInfo& srcInfo);
    /**
     * Fill the remainder of the destination with a single color
     *
     * @param dstStartRow
     * The destination row to fill from.
     *
     * @param numRows
     * The number of rows to fill.
     *
     * @param colorOrIndex
     * @param colorTable
     * If dstInfo.colorType() is kIndex8, colorOrIndex is assumed to be a uint8_t
     * index, and colorTable is ignored. Each 8-bit pixel will be set to (uint8_t)
     * index.
     *
     * If dstInfo.colorType() is kN32, colorOrIndex is treated differently depending on
     * whether colorTable is nullptr:
     *
     * A nullptr colorTable means colorOrIndex is treated as an SkPMColor (premul or
     * unpremul, depending on dstInfo.alphaType()). Each 4-byte pixel will be set to
     * colorOrIndex.

     * A non-nullptr colorTable means colorOrIndex is treated as a uint8_t index into
     * the colorTable. i.e. each 4-byte pixel will be set to
     * colorTable[(uint8_t) colorOrIndex].
     *
     * If dstInfo.colorType() is kGray, colorOrIndex is always treated as an 8-bit color.
     *
     * Other SkColorTypes are not supported.
     *
     * @param zeroInit
     * Indicates whether memory is already zero initialized.
     *
     */
    static void Fill(void* dstStartRow, const SkImageInfo& dstInfo, size_t dstRowBytes,
            uint32_t numRows, uint32_t colorOrIndex, const SkPMColor* colorTable,
            SkCodec::ZeroInitialized zeroInit);

    /**
     *  Swizzle a line. Generally this will be called height times, once
     *  for each row of source.
     *  By allowing the caller to pass in the dst pointer, we give the caller
     *  flexibility to use the swizzler even when the encoded data does not
     *  store the rows in order.  This also improves usability for scaled and
     *  subset decodes.
     *  @param dst Where we write the output.
     *  @param src The next row of the source data.
     *  @return A result code describing if the row was fully opaque, fully
     *          transparent, or neither
     */
    ResultAlpha swizzle(void* dst, const uint8_t* SK_RESTRICT src);

private:

    /**
     *  Method for converting raw data to Skia pixels.
     *  @param dstRow Row in which to write the resulting pixels.
     *  @param src Row of src data, in format specified by SrcConfig
     *  @param dstWidth Width in pixels of the destination
     *  @param bpp if bitsPerPixel % 8 == 0, deltaSrc is bytesPerPixel
     *             else, deltaSrc is bitsPerPixel
     *  @param deltaSrc bpp * sampleX
     *  @param ctable Colors (used for kIndex source).
     *  @param offset The offset before the first pixel to sample.
                        Is in bytes or bits based on what deltaSrc is in.
     */
    typedef ResultAlpha (*RowProc)(void* SK_RESTRICT dstRow,
                                   const uint8_t* SK_RESTRICT src,
                                   int dstWidth, int bpp, int deltaSrc, int offset,
                                   const SkPMColor ctable[]);

    const RowProc       fRowProc;
    const SkPMColor*    fColorTable;      // Unowned pointer
    const int           fDeltaSrc;        // if bitsPerPixel % 8 == 0
                                          //     deltaSrc is bytesPerPixel
                                          // else
                                          //     deltaSrc is bitsPerPixel
    const SkImageInfo   fDstInfo;
    int                 fCurrY;
    const int           fX0;              // first X coord to sample
    const int           fSampleX;         // step between X samples

    SkSwizzler(RowProc proc, const SkPMColor* ctable, int deltaSrc, const SkImageInfo& info, 
               int sampleX);
};
#endif // SkSwizzler_DEFINED