Revert of Delete SkImageDecoder

src/images/SkScaledBitmapSampler.cpp

Index: src/images/SkScaledBitmapSampler.cpp
diff --git a/src/images/SkScaledBitmapSampler.cpp b/src/images/SkScaledBitmapSampler.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..5ffd64889396b57ac8b5bf893f7f106212be00f1
--- /dev/null
+++ b/src/images/SkScaledBitmapSampler.cpp
@@ -0,0 +1,877 @@
+/*
+ * Copyright 2007 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.
+ */
+
+
+#include "SkScaledBitmapSampler.h"
+#include "SkBitmap.h"
+#include "SkColorPriv.h"
+#include "SkDither.h"
+#include "SkTypes.h"
+
+// 8888
+
+static bool Sample_Gray_D8888(void* SK_RESTRICT dstRow,
+                              const uint8_t* SK_RESTRICT src,
+                              int width, int deltaSrc, int, const SkPMColor[]) {
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkPackARGB32(0xFF, src[0], src[0], src[0]);
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_gray_to_8888_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Dither, unpremul, and skipZeroes have no effect
+    return Sample_Gray_D8888;
+}
+
+static bool Sample_RGBx_D8888(void* SK_RESTRICT dstRow,
+                              const uint8_t* SK_RESTRICT src,
+                              int width, int deltaSrc, int, const SkPMColor[]) {
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkPackARGB32(0xFF, src[0], src[1], src[2]);
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_RGBx_to_8888_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Dither, unpremul, and skipZeroes have no effect
+    return Sample_RGBx_D8888;
+}
+
+static bool Sample_RGBA_D8888(void* SK_RESTRICT dstRow,
+                              const uint8_t* SK_RESTRICT src,
+                              int width, int deltaSrc, int, const SkPMColor[]) {
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    unsigned alphaMask = 0xFF;
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        dst[x] = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+static bool Sample_RGBA_D8888_Unpremul(void* SK_RESTRICT dstRow,
+                                       const uint8_t* SK_RESTRICT src,
+                                       int width, int deltaSrc, int,
+                                       const SkPMColor[]) {
+    uint32_t* SK_RESTRICT dst = reinterpret_cast<uint32_t*>(dstRow);
+    unsigned alphaMask = 0xFF;
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        dst[x] = SkPackARGB32NoCheck(alpha, src[0], src[1], src[2]);
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+static bool Sample_RGBA_D8888_SkipZ(void* SK_RESTRICT dstRow,
+                                    const uint8_t* SK_RESTRICT src,
+                                    int width, int deltaSrc, int,
+                                    const SkPMColor[]) {
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    unsigned alphaMask = 0xFF;
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        if (0 != alpha) {
+            dst[x] = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+        }
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_RGBA_to_8888_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Dither has no effect.
+    if (!opts.fPremultiplyAlpha) {
+        // We could check each component for a zero, at the expense of extra checks.
+        // For now, just return unpremul.
+        return Sample_RGBA_D8888_Unpremul;
+    }
+    // Supply the versions that premultiply the colors
+    if (opts.fSkipZeros) {
+        return Sample_RGBA_D8888_SkipZ;
+    }
+    return Sample_RGBA_D8888;
+}
+
+// 565
+
+static bool Sample_Gray_D565(void* SK_RESTRICT dstRow,
+                             const uint8_t* SK_RESTRICT src,
+                             int width, int deltaSrc, int, const SkPMColor[]) {
+    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkPack888ToRGB16(src[0], src[0], src[0]);
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static bool Sample_Gray_D565_D(void* SK_RESTRICT dstRow,
+                               const uint8_t* SK_RESTRICT src,
+                           int width, int deltaSrc, int y, const SkPMColor[]) {
+    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
+    DITHER_565_SCAN(y);
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkDitherRGBTo565(src[0], src[0], src[0], DITHER_VALUE(x));
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_gray_to_565_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Unpremul and skip zeroes make no difference
+    if (opts.fDither) {
+        return Sample_Gray_D565_D;
+    }
+    return Sample_Gray_D565;
+}
+
+static bool Sample_RGBx_D565(void* SK_RESTRICT dstRow,
+                             const uint8_t* SK_RESTRICT src,
+                             int width, int deltaSrc, int, const SkPMColor[]) {
+    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkPack888ToRGB16(src[0], src[1], src[2]);
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static bool Sample_RGBx_D565_D(void* SK_RESTRICT dstRow,
+                               const uint8_t* SK_RESTRICT src,
+                               int width, int deltaSrc, int y,
+                               const SkPMColor[]) {
+    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
+    DITHER_565_SCAN(y);
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkDitherRGBTo565(src[0], src[1], src[2], DITHER_VALUE(x));
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_RGBx_to_565_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Unpremul and skip zeroes make no difference
+    if (opts.fDither) {
+        return Sample_RGBx_D565_D;
+    }
+    return Sample_RGBx_D565;
+}
+
+
+static bool Sample_D565_D565(void* SK_RESTRICT dstRow,
+                             const uint8_t* SK_RESTRICT src,
+                             int width, int deltaSrc, int, const SkPMColor[]) {
+    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
+    uint16_t* SK_RESTRICT castedSrc = (uint16_t*) src;
+    for (int x = 0; x < width; x++) {
+        dst[x] = castedSrc[0];
+        castedSrc += deltaSrc >> 1;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_565_to_565_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Unpremul, dither, and skip zeroes have no effect
+    return Sample_D565_D565;
+}
+
+// 4444
+
+static bool Sample_Gray_D4444(void* SK_RESTRICT dstRow,
+                              const uint8_t* SK_RESTRICT src,
+                              int width, int deltaSrc, int, const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    for (int x = 0; x < width; x++) {
+        unsigned gray = src[0] >> 4;
+        dst[x] = SkPackARGB4444(0xF, gray, gray, gray);
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static bool Sample_Gray_D4444_D(void* SK_RESTRICT dstRow,
+                                const uint8_t* SK_RESTRICT src,
+                            int width, int deltaSrc, int y, const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    DITHER_4444_SCAN(y);
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkDitherARGB32To4444(0xFF, src[0], src[0], src[0],
+                                      DITHER_VALUE(x));
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_gray_to_4444_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Skip zeroes and unpremul make no difference
+    if (opts.fDither) {
+        return Sample_Gray_D4444_D;
+    }
+    return Sample_Gray_D4444;
+}
+
+static bool Sample_RGBx_D4444(void* SK_RESTRICT dstRow,
+                              const uint8_t* SK_RESTRICT src,
+                              int width, int deltaSrc, int, const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkPackARGB4444(0xF, src[0] >> 4, src[1] >> 4, src[2] >> 4);
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static bool Sample_RGBx_D4444_D(void* SK_RESTRICT dstRow,
+                                const uint8_t* SK_RESTRICT src,
+                            int width, int deltaSrc, int y, const SkPMColor[]) {
+    SkPMColor16* dst = (SkPMColor16*)dstRow;
+    DITHER_4444_SCAN(y);
+
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkDitherARGB32To4444(0xFF, src[0], src[1], src[2],
+                                      DITHER_VALUE(x));
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_RGBx_to_4444_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Skip zeroes and unpremul make no difference
+    if (opts.fDither) {
+        return Sample_RGBx_D4444_D;
+    }
+    return Sample_RGBx_D4444;
+}
+
+static bool Sample_RGBA_D4444(void* SK_RESTRICT dstRow,
+                              const uint8_t* SK_RESTRICT src,
+                              int width, int deltaSrc, int, const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    unsigned alphaMask = 0xFF;
+
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        SkPMColor c = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+        dst[x] = SkPixel32ToPixel4444(c);
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+static bool Sample_RGBA_D4444_SkipZ(void* SK_RESTRICT dstRow,
+                                    const uint8_t* SK_RESTRICT src,
+                                    int width, int deltaSrc, int,
+                                    const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    unsigned alphaMask = 0xFF;
+
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        if (alpha != 0) {
+            SkPMColor c = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+            dst[x] = SkPixel32ToPixel4444(c);
+        }
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+
+static bool Sample_RGBA_D4444_D(void* SK_RESTRICT dstRow,
+                                const uint8_t* SK_RESTRICT src,
+                                int width, int deltaSrc, int y,
+                                const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    unsigned alphaMask = 0xFF;
+    DITHER_4444_SCAN(y);
+
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        SkPMColor c = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+        dst[x] = SkDitherARGB32To4444(c, DITHER_VALUE(x));
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+static bool Sample_RGBA_D4444_D_SkipZ(void* SK_RESTRICT dstRow,
+                                      const uint8_t* SK_RESTRICT src,
+                                      int width, int deltaSrc, int y,
+                                      const SkPMColor[]) {
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    unsigned alphaMask = 0xFF;
+    DITHER_4444_SCAN(y);
+
+    for (int x = 0; x < width; x++) {
+        unsigned alpha = src[3];
+        if (alpha != 0) {
+            SkPMColor c = SkPreMultiplyARGB(alpha, src[0], src[1], src[2]);
+            dst[x] = SkDitherARGB32To4444(c, DITHER_VALUE(x));
+        }
+        src += deltaSrc;
+        alphaMask &= alpha;
+    }
+    return alphaMask != 0xFF;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_RGBA_to_4444_proc(const SkScaledBitmapSampler::Options& opts) {
+    if (!opts.fPremultiplyAlpha) {
+        // Unpremultiplied is not supported for 4444
+        return nullptr;
+    }
+    if (opts.fSkipZeros) {
+        if (opts.fDither) {
+            return Sample_RGBA_D4444_D_SkipZ;
+        }
+        return Sample_RGBA_D4444_SkipZ;
+    }
+    if (opts.fDither) {
+        return Sample_RGBA_D4444_D;
+    }
+    return Sample_RGBA_D4444;
+}
+
+// Index
+
+#define A32_MASK_IN_PLACE   (SkPMColor)(SK_A32_MASK << SK_A32_SHIFT)
+
+static bool Sample_Index_D8888(void* SK_RESTRICT dstRow,
+                               const uint8_t* SK_RESTRICT src,
+                       int width, int deltaSrc, int, const SkPMColor ctable[]) {
+
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        cc &= c;
+        dst[x] = c;
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static bool Sample_Index_D8888_SkipZ(void* SK_RESTRICT dstRow,
+                                     const uint8_t* SK_RESTRICT src,
+                                     int width, int deltaSrc, int,
+                                     const SkPMColor ctable[]) {
+
+    SkPMColor* SK_RESTRICT dst = (SkPMColor*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        cc &= c;
+        if (c != 0) {
+            dst[x] = c;
+        }
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_index_to_8888_proc(const SkScaledBitmapSampler::Options& opts) {
+    // The caller is expected to have created the source colortable
+    // properly with respect to opts.fPremultiplyAlpha, so premul makes
+    // no difference here.
+    // Dither makes no difference
+    if (opts.fSkipZeros) {
+        return Sample_Index_D8888_SkipZ;
+    }
+    return Sample_Index_D8888;
+}
+
+static bool Sample_Index_D565(void* SK_RESTRICT dstRow,
+                               const uint8_t* SK_RESTRICT src,
+                       int width, int deltaSrc, int, const SkPMColor ctable[]) {
+
+    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
+    for (int x = 0; x < width; x++) {
+        dst[x] = SkPixel32ToPixel16(ctable[*src]);
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static bool Sample_Index_D565_D(void* SK_RESTRICT dstRow,
+                                const uint8_t* SK_RESTRICT src, int width,
+                                int deltaSrc, int y, const SkPMColor ctable[]) {
+
+    uint16_t* SK_RESTRICT dst = (uint16_t*)dstRow;
+    DITHER_565_SCAN(y);
+
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        dst[x] = SkDitherRGBTo565(SkGetPackedR32(c), SkGetPackedG32(c),
+                                  SkGetPackedB32(c), DITHER_VALUE(x));
+        src += deltaSrc;
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_index_to_565_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Unpremultiplied and skip zeroes make no difference
+    if (opts.fDither) {
+        return Sample_Index_D565_D;
+    }
+    return Sample_Index_D565;
+}
+
+static bool Sample_Index_D4444(void* SK_RESTRICT dstRow,
+                               const uint8_t* SK_RESTRICT src, int width,
+                               int deltaSrc, int y, const SkPMColor ctable[]) {
+
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        cc &= c;
+        dst[x] = SkPixel32ToPixel4444(c);
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static bool Sample_Index_D4444_D(void* SK_RESTRICT dstRow,
+                                 const uint8_t* SK_RESTRICT src, int width,
+                                int deltaSrc, int y, const SkPMColor ctable[]) {
+
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
+    DITHER_4444_SCAN(y);
+
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        cc &= c;
+        dst[x] = SkDitherARGB32To4444(c, DITHER_VALUE(x));
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static bool Sample_Index_D4444_SkipZ(void* SK_RESTRICT dstRow,
+                                     const uint8_t* SK_RESTRICT src, int width,
+                                     int deltaSrc, int y, const SkPMColor ctable[]) {
+
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        cc &= c;
+        if (c != 0) {
+            dst[x] = SkPixel32ToPixel4444(c);
+        }
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static bool Sample_Index_D4444_D_SkipZ(void* SK_RESTRICT dstRow,
+                                       const uint8_t* SK_RESTRICT src, int width,
+                                       int deltaSrc, int y, const SkPMColor ctable[]) {
+
+    SkPMColor16* SK_RESTRICT dst = (SkPMColor16*)dstRow;
+    SkPMColor cc = A32_MASK_IN_PLACE;
+    DITHER_4444_SCAN(y);
+
+    for (int x = 0; x < width; x++) {
+        SkPMColor c = ctable[*src];
+        cc &= c;
+        if (c != 0) {
+            dst[x] = SkDitherARGB32To4444(c, DITHER_VALUE(x));
+        }
+        src += deltaSrc;
+    }
+    return cc != A32_MASK_IN_PLACE;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_index_to_4444_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Unpremul not allowed
+    if (!opts.fPremultiplyAlpha) {
+        return nullptr;
+    }
+    if (opts.fSkipZeros) {
+        if (opts.fDither) {
+            return Sample_Index_D4444_D_SkipZ;
+        }
+        return Sample_Index_D4444_SkipZ;
+    }
+    if (opts.fDither) {
+        return Sample_Index_D4444_D;
+    }
+    return Sample_Index_D4444;
+}
+
+static bool Sample_Index_DI(void* SK_RESTRICT dstRow,
+                            const uint8_t* SK_RESTRICT src,
+                            int width, int deltaSrc, int, const SkPMColor[]) {
+    if (1 == deltaSrc) {
+        memcpy(dstRow, src, width);
+    } else {
+        uint8_t* SK_RESTRICT dst = (uint8_t*)dstRow;
+        for (int x = 0; x < width; x++) {
+            dst[x] = src[0];
+            src += deltaSrc;
+        }
+    }
+    return false;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_index_to_index_proc(const SkScaledBitmapSampler::Options& opts) {
+    // Unpremul not allowed
+    if (!opts.fPremultiplyAlpha) {
+        return nullptr;
+    }
+    // Ignore dither and skip zeroes
+    return Sample_Index_DI;
+}
+
+// A8
+static bool Sample_Gray_DA8(void* SK_RESTRICT dstRow,
+                            const uint8_t* SK_RESTRICT src,
+                            int width, int deltaSrc, int,
+                            const SkPMColor[]) {
+    // Sampling Gray to A8 uses the same function as Index to Index8,
+    // except we assume that there is alpha for speed, since an A8
+    // bitmap with no alpha is not interesting.
+    (void) Sample_Index_DI(dstRow, src, width, deltaSrc, /* y unused */ 0,
+                           /* ctable unused */ nullptr);
+    return true;
+}
+
+static SkScaledBitmapSampler::RowProc
+get_gray_to_A8_proc(const SkScaledBitmapSampler::Options& opts) {
+    if (!opts.fPremultiplyAlpha) {
+        return nullptr;
+    }
+    // Ignore skip and dither.
+    return Sample_Gray_DA8;
+}
+
+typedef SkScaledBitmapSampler::RowProc (*RowProcChooser)(const SkScaledBitmapSampler::Options&);
+///////////////////////////////////////////////////////////////////////////////
+
+#include "SkScaledBitmapSampler.h"
+
+SkScaledBitmapSampler::SkScaledBitmapSampler(int width, int height,
+                                             int sampleSize) {
+    fCTable = nullptr;
+    fDstRow = nullptr;
+    fRowProc = nullptr;
+
+    if (width <= 0 || height <= 0) {
+        sk_throw();
+    }
+
+    SkDEBUGCODE(fSampleMode = kUninitialized_SampleMode);
+
+    if (sampleSize <= 1) {
+        fScaledWidth = width;
+        fScaledHeight = height;
+        fX0 = fY0 = 0;
+        fDX = fDY = 1;
+        return;
+    }
+
+    int dx = SkMin32(sampleSize, width);
+    int dy = SkMin32(sampleSize, height);
+
+    fScaledWidth = width / dx;
+    fScaledHeight = height / dy;
+
+    SkASSERT(fScaledWidth > 0);
+    SkASSERT(fScaledHeight > 0);
+
+    fX0 = dx >> 1;
+    fY0 = dy >> 1;
+
+    SkASSERT(fX0 >= 0 && fX0 < width);
+    SkASSERT(fY0 >= 0 && fY0 < height);
+
+    fDX = dx;
+    fDY = dy;
+
+    SkASSERT(fDX > 0 && (fX0 + fDX * (fScaledWidth - 1)) < width);
+    SkASSERT(fDY > 0 && (fY0 + fDY * (fScaledHeight - 1)) < height);
+}
+
+bool SkScaledBitmapSampler::begin(SkBitmap* dst, SrcConfig sc,
+                                  const Options& opts,
+                                  const SkPMColor ctable[]) {
+    static const RowProcChooser gProcChoosers[] = {
+        get_gray_to_8888_proc,
+        get_RGBx_to_8888_proc,
+        get_RGBA_to_8888_proc,
+        get_index_to_8888_proc,
+        nullptr, // 565 to 8888
+
+        get_gray_to_565_proc,
+        get_RGBx_to_565_proc,
+        get_RGBx_to_565_proc, // The source alpha will be ignored.
+        get_index_to_565_proc,
+        get_565_to_565_proc,
+
+        get_gray_to_4444_proc,
+        get_RGBx_to_4444_proc,
+        get_RGBA_to_4444_proc,
+        get_index_to_4444_proc,
+        nullptr, // 565 to 4444
+
+        nullptr, // gray to index
+        nullptr, // rgbx to index
+        nullptr, // rgba to index
+        get_index_to_index_proc,
+        nullptr, // 565 to index
+
+        get_gray_to_A8_proc,
+        nullptr, // rgbx to a8
+        nullptr, // rgba to a8
+        nullptr, // index to a8
+        nullptr, // 565 to a8
+    };
+
+    // The jump between dst configs in the table
+    static const int gProcDstConfigSpan = 5;
+    static_assert(SK_ARRAY_COUNT(gProcChoosers) == 5 * gProcDstConfigSpan,
+                  "gProcs_has_the_wrong_number_of_entries");
+
+    fCTable = ctable;
+
+    int index = 0;
+    switch (sc) {
+        case SkScaledBitmapSampler::kGray:
+            fSrcPixelSize = 1;
+            index += 0;
+            break;
+        case SkScaledBitmapSampler::kRGB:
+            fSrcPixelSize = 3;
+            index += 1;
+            break;
+        case SkScaledBitmapSampler::kRGBX:
+            fSrcPixelSize = 4;
+            index += 1;
+            break;
+        case SkScaledBitmapSampler::kRGBA:
+            fSrcPixelSize = 4;
+            index += 2;
+            break;
+        case SkScaledBitmapSampler::kIndex:
+            fSrcPixelSize = 1;
+            index += 3;
+            break;
+        case SkScaledBitmapSampler::kRGB_565:
+            fSrcPixelSize = 2;
+            index += 4;
+            break;
+        default:
+            return false;
+    }
+
+    switch (dst->colorType()) {
+        case kN32_SkColorType:
+            index += 0 * gProcDstConfigSpan;
+            break;
+        case kRGB_565_SkColorType:
+            index += 1 * gProcDstConfigSpan;
+            break;
+        case kARGB_4444_SkColorType:
+            index += 2 * gProcDstConfigSpan;
+            break;
+        case kIndex_8_SkColorType:
+            index += 3 * gProcDstConfigSpan;
+            break;
+        case kAlpha_8_SkColorType:
+            index += 4 * gProcDstConfigSpan;
+            break;
+        default:
+            return false;
+    }
+
+    RowProcChooser chooser = gProcChoosers[index];
+    if (nullptr == chooser) {
+        fRowProc = nullptr;
+    } else {
+        fRowProc = chooser(opts);
+    }
+    fDstRow = (char*)dst->getPixels();
+    fDstRowBytes = dst->rowBytes();
+    fCurrY = 0;
+    return fRowProc != nullptr;
+}
+
+bool SkScaledBitmapSampler::begin(SkBitmap* dst, SrcConfig sc,
+                                  const SkImageDecoder& decoder,
+                                  const SkPMColor ctable[]) {
+    return this->begin(dst, sc, Options(decoder), ctable);
+}
+
+bool SkScaledBitmapSampler::next(const uint8_t* SK_RESTRICT src) {
+    SkASSERT(kInterlaced_SampleMode != fSampleMode);
+    SkDEBUGCODE(fSampleMode = kConsecutive_SampleMode);
+    SkASSERT((unsigned)fCurrY < (unsigned)fScaledHeight);
+
+    bool hadAlpha = fRowProc(fDstRow, src + fX0 * fSrcPixelSize, fScaledWidth,
+                             fDX * fSrcPixelSize, fCurrY, fCTable);
+    fDstRow += fDstRowBytes;
+    fCurrY += 1;
+    return hadAlpha;
+}
+
+bool SkScaledBitmapSampler::sampleInterlaced(const uint8_t* SK_RESTRICT src, int srcY) {
+    SkASSERT(kConsecutive_SampleMode != fSampleMode);
+    SkDEBUGCODE(fSampleMode = kInterlaced_SampleMode);
+    // Any line that should be a part of the destination can be created by the formula:
+    // fY0 + (some multiplier) * fDY
+    // so if srcY - fY0 is not an integer multiple of fDY that srcY will be skipped.
+    const int srcYMinusY0 = srcY - fY0;
+    if (srcYMinusY0 % fDY != 0) {
+        // This line is not part of the output, so return false for alpha, since we have
+        // not added an alpha to the output.
+        return false;
+    }
+    // Unlike in next(), where the data is used sequentially, this function skips around,
+    // so fDstRow and fCurrY are never updated. fDstRow must always be the starting point
+    // of the destination bitmap's pixels, which is used to calculate the destination row
+    // each time this function is called.
+    const int dstY = srcYMinusY0 / fDY;
+    if (dstY >= fScaledHeight) {
+        return false;
+    }
+    char* dstRow = fDstRow + dstY * fDstRowBytes;
+    return fRowProc(dstRow, src + fX0 * fSrcPixelSize, fScaledWidth,
+                    fDX * fSrcPixelSize, dstY, fCTable);
+}
+
+#ifdef SK_DEBUG
+// The following code is for a test to ensure that changing the method to get the right row proc
+// did not change the row proc unintentionally. Tested by ImageDecodingTest.cpp
+
+// friend of SkScaledBitmapSampler solely for the purpose of accessing fRowProc.
+class RowProcTester {
+public:
+    static SkScaledBitmapSampler::RowProc getRowProc(const SkScaledBitmapSampler& sampler) {
+        return sampler.fRowProc;
+    }
+};
+
+
+// Table showing the expected RowProc for each combination of inputs.
+// Table formated as follows:
+// Each group of 5 consecutive rows represents sampling from a single
+// SkScaledBitmapSampler::SrcConfig.
+// Within each set, each row represents a different destination SkBitmap::Config
+// Each column represents a different combination of dither and unpremul.
+// D = dither   ~D = no dither
+// U = unpremul ~U = no unpremul
+//  ~D~U                D~U                     ~DU                         DU
+SkScaledBitmapSampler::RowProc gTestProcs[] = {
+    // Gray
+    Sample_Gray_DA8,    Sample_Gray_DA8,        nullptr,                       nullptr,                       // to A8
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to Index8
+    Sample_Gray_D565,   Sample_Gray_D565_D,     Sample_Gray_D565,           Sample_Gray_D565_D,         // to 565
+    Sample_Gray_D4444,  Sample_Gray_D4444_D,    Sample_Gray_D4444,          Sample_Gray_D4444_D,        // to 4444
+    Sample_Gray_D8888,  Sample_Gray_D8888,      Sample_Gray_D8888,          Sample_Gray_D8888,          // to 8888
+    // Index
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to A8
+    Sample_Index_DI,    Sample_Index_DI,        nullptr,                       nullptr,                       // to Index8
+    Sample_Index_D565,  Sample_Index_D565_D,    Sample_Index_D565,          Sample_Index_D565_D,        // to 565
+    Sample_Index_D4444, Sample_Index_D4444_D,   nullptr,                       nullptr,                       // to 4444
+    Sample_Index_D8888, Sample_Index_D8888,     Sample_Index_D8888,         Sample_Index_D8888,         // to 8888
+    // RGB
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to A8
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to Index8
+    Sample_RGBx_D565,   Sample_RGBx_D565_D,     Sample_RGBx_D565,           Sample_RGBx_D565_D,         // to 565
+    Sample_RGBx_D4444,  Sample_RGBx_D4444_D,    Sample_RGBx_D4444,          Sample_RGBx_D4444_D,        // to 4444
+    Sample_RGBx_D8888,  Sample_RGBx_D8888,      Sample_RGBx_D8888,          Sample_RGBx_D8888,          // to 8888
+    // RGBx is the same as RGB
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to A8
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to Index8
+    Sample_RGBx_D565,   Sample_RGBx_D565_D,     Sample_RGBx_D565,           Sample_RGBx_D565_D,         // to 565
+    Sample_RGBx_D4444,  Sample_RGBx_D4444_D,    Sample_RGBx_D4444,          Sample_RGBx_D4444_D,        // to 4444
+    Sample_RGBx_D8888,  Sample_RGBx_D8888,      Sample_RGBx_D8888,          Sample_RGBx_D8888,          // to 8888
+    // RGBA
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to A8
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to Index8
+    Sample_RGBx_D565,   Sample_RGBx_D565_D,     Sample_RGBx_D565,           Sample_RGBx_D565_D,         // to 565
+    Sample_RGBA_D4444,  Sample_RGBA_D4444_D,    nullptr,                       nullptr,                       // to 4444
+    Sample_RGBA_D8888,  Sample_RGBA_D8888,      Sample_RGBA_D8888_Unpremul, Sample_RGBA_D8888_Unpremul, // to 8888
+    // RGB_565
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to A8
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to Index8
+    Sample_D565_D565,   Sample_D565_D565,       Sample_D565_D565,           Sample_D565_D565,           // to 565
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to 4444
+    nullptr,               nullptr,                   nullptr,                       nullptr,                       // to 8888
+};
+
+// Dummy class that allows instantiation of an ImageDecoder, so begin can query its fields.
+class DummyDecoder : public SkImageDecoder {
+public:
+    DummyDecoder() {}
+protected:
+    Result onDecode(SkStream*, SkBitmap*, SkImageDecoder::Mode) override {
+        return kFailure;
+    }
+};
+
+void test_row_proc_choice();
+void test_row_proc_choice() {
+    const SkColorType colorTypes[] = {
+        kAlpha_8_SkColorType, kIndex_8_SkColorType, kRGB_565_SkColorType, kARGB_4444_SkColorType,
+        kN32_SkColorType
+    };
+
+    SkBitmap dummyBitmap;
+    DummyDecoder dummyDecoder;
+    size_t procCounter = 0;
+    for (int sc = SkScaledBitmapSampler::kGray; sc <= SkScaledBitmapSampler::kRGB_565; ++sc) {
+        for (size_t c = 0; c < SK_ARRAY_COUNT(colorTypes); ++c) {
+            for (int unpremul = 0; unpremul <= 1; ++unpremul) {
+                for (int dither = 0; dither <= 1; ++dither) {
+                    // Arbitrary width/height/sampleSize to allow SkScaledBitmapSampler to
+                    // be considered valid.
+                    SkScaledBitmapSampler sampler(10, 10, 1);
+                    dummyBitmap.setInfo(SkImageInfo::Make(10, 10,
+                                                          colorTypes[c], kPremul_SkAlphaType));
+                    dummyDecoder.setDitherImage(SkToBool(dither));
+                    dummyDecoder.setRequireUnpremultipliedColors(SkToBool(unpremul));
+                    sampler.begin(&dummyBitmap, (SkScaledBitmapSampler::SrcConfig) sc,
+                                  dummyDecoder);
+                    SkScaledBitmapSampler::RowProc expected = gTestProcs[procCounter];
+                    SkScaledBitmapSampler::RowProc actual = RowProcTester::getRowProc(sampler);
+                    SkASSERT(expected == actual);
+                    procCounter++;
+                }
+            }
+        }
+    }
+    SkASSERT(SK_ARRAY_COUNT(gTestProcs) == procCounter);
+}
+#endif // SK_DEBUG