Revert "Remove deadcode for sRGB image shading."

This reverts commit 51f6a0f89e55b2c0f102aa7963320a23c586e71d.

Reason for revert: try to fix chrome roll

Original change's description:
> Remove deadcode for sRGB image shading.
> 
> Change-Id: I9d98da67d97b64ab55cf44b9ae447882dccda1ca
> Reviewed-on: https://skia-review.googlesource.com/20695
> Reviewed-by: Mike Klein <mtklein@chromium.org>
> Commit-Queue: Herb Derby <herb@google.com>

TBR=mtklein@chromium.org,mtklein@google.com,herb@google.com,reed@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: I90409a08409177d9dc3b094d736af0fdaf7d6cdd
Reviewed-on: https://skia-review.googlesource.com/20824
Reviewed-by: Mike Reed <reed@google.com>
Commit-Queue: Mike Reed <reed@google.com>

1 files changed, 1041 insertions, 0 deletions

diff --git a/src/core/SkLinearBitmapPipeline_sample.h b/src/core/SkLinearBitmapPipeline_sample.h
new file mode 100644
index 0000000000..a7f5d7383e
--- /dev/null
+++ b/src/core/SkLinearBitmapPipeline_sample.h
@@ -0,0 +1,1041 @@
+/*
+ * Copyright 2016 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkLinearBitmapPipeline_sampler_DEFINED
+#define SkLinearBitmapPipeline_sampler_DEFINED
+
+#include <tuple>
+
+#include "SkAutoMalloc.h"
+#include "SkColor.h"
+#include "SkColorPriv.h"
+#include "SkFixed.h"  // for SkFixed1 only. Don't use SkFixed in this file.
+#include "SkHalf.h"
+#include "SkLinearBitmapPipeline_core.h"
+#include "SkNx.h"
+#include "SkPM4fPriv.h"
+
+namespace {
+// Explaination of the math:
+//              1 - x      x
+//           +--------+--------+
+//           |        |        |
+//  1 - y    |  px00  |  px10  |
+//           |        |        |
+//           +--------+--------+
+//           |        |        |
+//    y      |  px01  |  px11  |
+//           |        |        |
+//           +--------+--------+
+//
+//
+// Given a pixelxy each is multiplied by a different factor derived from the fractional part of x
+// and y:
+// * px00 -> (1 - x)(1 - y) = 1 - x - y + xy
+// * px10 -> x(1 - y) = x - xy
+// * px01 -> (1 - x)y = y - xy
+// * px11 -> xy
+// So x * y is calculated first and then used to calculate all the other factors.
+static Sk4s SK_VECTORCALL bilerp4(Sk4s xs, Sk4s ys, Sk4f px00, Sk4f px10,
+                                                    Sk4f px01, Sk4f px11) {
+    // Calculate fractional xs and ys.
+    Sk4s fxs = xs - xs.floor();
+    Sk4s fys = ys - ys.floor();
+    Sk4s fxys{fxs * fys};
+    Sk4f sum = px11 * fxys;
+    sum = sum + px01 * (fys - fxys);
+    sum = sum + px10 * (fxs - fxys);
+    sum = sum + px00 * (Sk4f{1.0f} - fxs - fys + fxys);
+    return sum;
+}
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+// PixelGetter is the lowest level interface to the source data. There is a PixelConverter for each
+// of the different SkColorTypes.
+template <SkColorType, SkGammaType> class PixelConverter;
+
+// Alpha handling:
+//   The alpha from the paint (tintColor) is used in the blend part of the pipeline to modulate
+// the entire bitmap. So, the tint color is given an alpha of 1.0 so that the later alpha can
+// modulate this color later.
+template <>
+class PixelConverter<kAlpha_8_SkColorType, kLinear_SkGammaType> {
+public:
+    using Element = uint8_t;
+    PixelConverter(const SkPixmap& srcPixmap, SkColor tintColor) {
+        fTintColor = SkColor4f::FromColor(tintColor);
+        fTintColor.fA = 1.0f;
+    }
+
+    Sk4f toSk4f(const Element pixel) const {
+        return Sk4f::Load(&fTintColor) * (pixel * (1.0f/255.0f));
+    }
+
+private:
+    SkColor4f fTintColor;
+};
+
+template <SkGammaType gammaType>
+static inline Sk4f pmcolor_to_rgba(SkPMColor pixel) {
+    return swizzle_rb_if_bgra(
+            (gammaType == kSRGB_SkGammaType) ? Sk4f_fromS32(pixel)
+                                             : Sk4f_fromL32(pixel));
+}
+
+template <SkGammaType gammaType>
+class PixelConverter<kRGB_565_SkColorType, gammaType> {
+public:
+    using Element = uint16_t;
+    PixelConverter(const SkPixmap& srcPixmap) { }
+
+    Sk4f toSk4f(Element pixel) const {
+        return pmcolor_to_rgba<gammaType>(SkPixel16ToPixel32(pixel));
+    }
+};
+
+template <SkGammaType gammaType>
+class PixelConverter<kARGB_4444_SkColorType, gammaType> {
+public:
+    using Element = uint16_t;
+    PixelConverter(const SkPixmap& srcPixmap) { }
+
+    Sk4f toSk4f(Element pixel) const {
+        return pmcolor_to_rgba<gammaType>(SkPixel4444ToPixel32(pixel));
+    }
+};
+
+template <SkGammaType gammaType>
+class PixelConverter<kRGBA_8888_SkColorType, gammaType> {
+public:
+    using Element = uint32_t;
+    PixelConverter(const SkPixmap& srcPixmap) { }
+
+    Sk4f toSk4f(Element pixel) const {
+        return gammaType == kSRGB_SkGammaType
+               ? Sk4f_fromS32(pixel)
+               : Sk4f_fromL32(pixel);
+    }
+};
+
+template <SkGammaType gammaType>
+class PixelConverter<kBGRA_8888_SkColorType, gammaType> {
+public:
+    using Element = uint32_t;
+    PixelConverter(const SkPixmap& srcPixmap) { }
+
+    Sk4f toSk4f(Element pixel) const {
+        return swizzle_rb(
+                   gammaType == kSRGB_SkGammaType ? Sk4f_fromS32(pixel) : Sk4f_fromL32(pixel));
+    }
+};
+
+template <SkGammaType gammaType>
+class PixelConverter<kIndex_8_SkColorType, gammaType> {
+public:
+    using Element = uint8_t;
+    PixelConverter(const SkPixmap& srcPixmap)
+    : fColorTableSize(srcPixmap.ctable()->count()){
+        SkColorTable* skColorTable = srcPixmap.ctable();
+        SkASSERT(skColorTable != nullptr);
+
+        fColorTable = (Sk4f*)SkAlign16((intptr_t)fColorTableStorage.get());
+        for (int i = 0; i < fColorTableSize; i++) {
+            fColorTable[i] = pmcolor_to_rgba<gammaType>((*skColorTable)[i]);
+        }
+    }
+
+    PixelConverter(const PixelConverter& strategy)
+    : fColorTableSize{strategy.fColorTableSize}{
+        fColorTable = (Sk4f*)SkAlign16((intptr_t)fColorTableStorage.get());
+        for (int i = 0; i < fColorTableSize; i++) {
+            fColorTable[i] = strategy.fColorTable[i];
+        }
+    }
+
+    Sk4f toSk4f(Element index) const {
+        return fColorTable[index];
+    }
+
+private:
+    static const size_t kColorTableSize = sizeof(Sk4f[256]) + 12;
+    const int           fColorTableSize;
+    SkAutoMalloc        fColorTableStorage{kColorTableSize};
+    Sk4f*               fColorTable;
+};
+
+template <SkGammaType gammaType>
+class PixelConverter<kGray_8_SkColorType, gammaType> {
+public:
+    using Element = uint8_t;
+    PixelConverter(const SkPixmap& srcPixmap) { }
+
+    Sk4f toSk4f(Element pixel) const {
+        float gray = (gammaType == kSRGB_SkGammaType)
+            ? sk_linear_from_srgb[pixel]
+            : pixel * (1/255.0f);
+        return {gray, gray, gray, 1.0f};
+    }
+};
+
+template <>
+class PixelConverter<kRGBA_F16_SkColorType, kLinear_SkGammaType> {
+public:
+    using Element = uint64_t;
+    PixelConverter(const SkPixmap& srcPixmap) { }
+
+    Sk4f toSk4f(const Element pixel) const {
+        return SkHalfToFloat_finite_ftz(pixel);
+    }
+};
+
+class PixelAccessorShim {
+public:
+    explicit PixelAccessorShim(SkLinearBitmapPipeline::PixelAccessorInterface* accessor)
+        : fPixelAccessor(accessor) { }
+
+    void SK_VECTORCALL getFewPixels(
+        int n, Sk4i xs, Sk4i ys, Sk4f* px0, Sk4f* px1, Sk4f* px2) const {
+        fPixelAccessor->getFewPixels(n, xs, ys, px0, px1, px2);
+    }
+
+    void SK_VECTORCALL get4Pixels(
+        Sk4i xs, Sk4i ys, Sk4f* px0, Sk4f* px1, Sk4f* px2, Sk4f* px3) const {
+        fPixelAccessor->get4Pixels(xs, ys, px0, px1, px2, px3);
+    }
+
+    void get4Pixels(
+        const void* src, int index, Sk4f* px0, Sk4f* px1, Sk4f* px2, Sk4f* px3) const {
+        fPixelAccessor->get4Pixels(src, index, px0, px1, px2, px3);
+    }
+
+    Sk4f getPixelFromRow(const void* row, int index) const {
+        return fPixelAccessor->getPixelFromRow(row, index);
+    }
+
+    Sk4f getPixelAt(int index) const {
+        return fPixelAccessor->getPixelAt(index);
+    }
+
+    const void* row(int y) const {
+        return fPixelAccessor->row(y);
+    }
+
+private:
+    SkLinearBitmapPipeline::PixelAccessorInterface* const fPixelAccessor;
+};
+
+////////////////////////////////////////////////////////////////////////////////////////////////////
+// PixelAccessor handles all the same plumbing for all the PixelGetters.
+template <SkColorType colorType, SkGammaType gammaType>
+class PixelAccessor final : public SkLinearBitmapPipeline::PixelAccessorInterface {
+    using Element = typename PixelConverter<colorType, gammaType>::Element;
+public:
+    template <typename... Args>
+    PixelAccessor(const SkPixmap& srcPixmap, Args&&... args)
+        : fSrc{static_cast<const Element*>(srcPixmap.addr())}
+        , fWidth{srcPixmap.rowBytesAsPixels()}
+        , fConverter{srcPixmap, std::move<Args>(args)...} { }
+
+    void SK_VECTORCALL getFewPixels (
+        int n, Sk4i xs, Sk4i ys, Sk4f* px0, Sk4f* px1, Sk4f* px2) const override {
+        Sk4i bufferLoc = ys * fWidth + xs;
+        switch (n) {
+            case 3:
+                *px2 = this->getPixelAt(bufferLoc[2]);
+            case 2:
+                *px1 = this->getPixelAt(bufferLoc[1]);
+            case 1:
+                *px0 = this->getPixelAt(bufferLoc[0]);
+            default:
+                break;
+        }
+    }
+
+    void SK_VECTORCALL get4Pixels(
+        Sk4i xs, Sk4i ys, Sk4f* px0, Sk4f* px1, Sk4f* px2, Sk4f* px3) const override {
+        Sk4i bufferLoc = ys * fWidth + xs;
+        *px0 = this->getPixelAt(bufferLoc[0]);
+        *px1 = this->getPixelAt(bufferLoc[1]);
+        *px2 = this->getPixelAt(bufferLoc[2]);
+        *px3 = this->getPixelAt(bufferLoc[3]);
+    }
+
+    void get4Pixels(
+        const void* src, int index, Sk4f* px0, Sk4f* px1, Sk4f* px2, Sk4f* px3) const override {
+        *px0 = this->getPixelFromRow(src, index + 0);
+        *px1 = this->getPixelFromRow(src, index + 1);
+        *px2 = this->getPixelFromRow(src, index + 2);
+        *px3 = this->getPixelFromRow(src, index + 3);
+    }
+
+    Sk4f getPixelFromRow(const void* row, int index) const override {
+        const Element* src = static_cast<const Element*>(row);
+        return fConverter.toSk4f(src[index]);
+    }
+
+    Sk4f getPixelAt(int index) const override {
+        return this->getPixelFromRow(fSrc, index);
+    }
+
+    const void* row(int y) const override { return fSrc + y * fWidth; }
+
+private:
+    const Element* const                 fSrc;
+    const int                            fWidth;
+    PixelConverter<colorType, gammaType> fConverter;
+};
+
+// We're moving through source space at a rate of 1 source pixel per 1 dst pixel.
+// We'll never re-use pixels, but we can at least load contiguous pixels.
+template <typename Next, typename Strategy>
+static void src_strategy_blend(Span span, Next* next, Strategy* strategy) {
+    SkPoint start;
+    SkScalar length;
+    int count;
+    std::tie(start, length, count) = span;
+    int ix = SkScalarFloorToInt(X(start));
+    const void* row = strategy->row((int)std::floor(Y(start)));
+    if (length > 0) {
+        while (count >= 4) {
+            Sk4f px0, px1, px2, px3;
+            strategy->get4Pixels(row, ix, &px0, &px1, &px2, &px3);
+            next->blend4Pixels(px0, px1, px2, px3);
+            ix += 4;
+            count -= 4;
+        }
+
+        while (count > 0) {
+            next->blendPixel(strategy->getPixelFromRow(row, ix));
+            ix += 1;
+            count -= 1;
+        }
+    } else {
+        while (count >= 4) {
+            Sk4f px0, px1, px2, px3;
+            strategy->get4Pixels(row, ix - 3, &px3, &px2, &px1, &px0);
+            next->blend4Pixels(px0, px1, px2, px3);
+            ix -= 4;
+            count -= 4;
+        }
+
+        while (count > 0) {
+            next->blendPixel(strategy->getPixelFromRow(row, ix));
+            ix -= 1;
+            count -= 1;
+        }
+    }
+}
+
+// -- NearestNeighborSampler -----------------------------------------------------------------------
+// NearestNeighborSampler - use nearest neighbor filtering to create runs of destination pixels.
+template<typename Accessor, typename Next>
+class NearestNeighborSampler : public SkLinearBitmapPipeline::SampleProcessorInterface {
+public:
+    template<typename... Args>
+    NearestNeighborSampler(SkLinearBitmapPipeline::BlendProcessorInterface* next, Args&& ... args)
+    : fNext{next}, fAccessor{std::forward<Args>(args)...} { }
+
+    NearestNeighborSampler(SkLinearBitmapPipeline::BlendProcessorInterface* next,
+    const NearestNeighborSampler& sampler)
+    : fNext{next}, fAccessor{sampler.fAccessor} { }
+
+    void SK_VECTORCALL pointListFew(int n, Sk4s xs, Sk4s ys) override {
+        SkASSERT(0 < n && n < 4);
+        Sk4f px0, px1, px2;
+        fAccessor.getFewPixels(n, SkNx_cast<int>(xs), SkNx_cast<int>(ys), &px0, &px1, &px2);
+        if (n >= 1) fNext->blendPixel(px0);
+        if (n >= 2) fNext->blendPixel(px1);
+        if (n >= 3) fNext->blendPixel(px2);
+    }
+
+    void SK_VECTORCALL pointList4(Sk4s xs, Sk4s ys) override {
+        Sk4f px0, px1, px2, px3;
+        fAccessor.get4Pixels(SkNx_cast<int>(xs), SkNx_cast<int>(ys), &px0, &px1, &px2, &px3);
+        fNext->blend4Pixels(px0, px1, px2, px3);
+    }
+
+    void pointSpan(Span span) override {
+        SkASSERT(!span.isEmpty());
+        SkPoint start;
+        SkScalar length;
+        int count;
+        std::tie(start, length, count) = span;
+        SkScalar absLength = SkScalarAbs(length);
+        if (absLength < (count - 1)) {
+            this->spanSlowRate(span);
+        } else if (absLength == (count - 1)) {
+            src_strategy_blend(span, fNext, &fAccessor);
+        } else {
+            this->spanFastRate(span);
+        }
+    }
+
+    void repeatSpan(Span span, int32_t repeatCount) override {
+        while (repeatCount > 0) {
+            this->pointSpan(span);
+            repeatCount--;
+        }
+    }
+
+private:
+    // When moving through source space more slowly than dst space (zoomed in),
+    // we'll be sampling from the same source pixel more than once.
+    void spanSlowRate(Span span) {
+        SkPoint start; SkScalar length; int count;
+        std::tie(start, length, count) = span;
+        SkScalar x = X(start);
+        // fx is a fixed 48.16 number.
+        int64_t fx = static_cast<int64_t>(x * SK_Fixed1);
+        SkScalar dx = length / (count - 1);
+        // fdx is a fixed 48.16 number.
+        int64_t fdx = static_cast<int64_t>(dx * SK_Fixed1);
+
+        const void* row = fAccessor.row((int)std::floor(Y(start)));
+        Next* next = fNext;
+
+        int64_t ix = fx >> 16;
+        int64_t prevIX = ix;
+        Sk4f fpixel = fAccessor.getPixelFromRow(row, ix);
+
+        // When dx is less than one, each pixel is used more than once. Using the fixed point fx
+        // allows the code to quickly check that the same pixel is being used. The code uses this
+        // same pixel check to do the sRGB and normalization only once.
+        auto getNextPixel = [&]() {
+            if (ix != prevIX) {
+                fpixel = fAccessor.getPixelFromRow(row, ix);
+                prevIX = ix;
+            }
+            fx += fdx;
+            ix = fx >> 16;
+            return fpixel;
+        };
+
+        while (count >= 4) {
+            Sk4f px0 = getNextPixel();
+            Sk4f px1 = getNextPixel();
+            Sk4f px2 = getNextPixel();
+            Sk4f px3 = getNextPixel();
+            next->blend4Pixels(px0, px1, px2, px3);
+            count -= 4;
+        }
+        while (count > 0) {
+            next->blendPixel(getNextPixel());
+            count -= 1;
+        }
+    }
+
+    // We're moving through source space at a rate of 1 source pixel per 1 dst pixel.
+    // We'll never re-use pixels, but we can at least load contiguous pixels.
+    void spanUnitRate(Span span) {
+        src_strategy_blend(span, fNext, &fAccessor);
+    }
+
+    // We're moving through source space faster than dst (zoomed out),
+    // so we'll never reuse a source pixel or be able to do contiguous loads.
+    void spanFastRate(Span span) {
+        span_fallback(span, this);
+    }
+
+    Next* const fNext;
+    Accessor    fAccessor;
+};
+
+// From an edgeType, the integer value of a pixel vs, and the integer value of the extreme edge
+// vMax, take the point which might be off the tile by one pixel and either wrap it or pin it to
+// generate the right pixel. The value vs is on the interval [-1, vMax + 1]. It produces a value
+// on the interval [0, vMax].
+// Note: vMax is not width or height, but width-1 or height-1 because it is the largest valid pixel.
+static inline int adjust_edge(SkShader::TileMode edgeType, int vs, int vMax) {
+    SkASSERT(-1 <= vs && vs <= vMax + 1);
+    switch (edgeType) {
+        case SkShader::kClamp_TileMode:
+        case SkShader::kMirror_TileMode:
+            vs = std::max(vs, 0);
+            vs = std::min(vs, vMax);
+            break;
+        case SkShader::kRepeat_TileMode:
+            vs = (vs <= vMax) ? vs : 0;
+            vs =    (vs >= 0) ? vs : vMax;
+            break;
+    }
+    SkASSERT(0 <= vs && vs <= vMax);
+    return vs;
+}
+
+// From a sample point on the tile, return the top or left filter value.
+// The result r should be in the range (0, 1]. Since this represents the weight given to the top
+// left element, then if x == 0.5 the filter value should be 1.0.
+// The input sample point must be on the tile, therefore it must be >= 0.
+static SkScalar sample_to_filter(SkScalar x) {
+    SkASSERT(x >= 0.0f);
+    // The usual form of the top or left edge is x - .5, but since we are working on the unit
+    // square, then x + .5 works just as well. This also guarantees that v > 0.0 allowing the use
+    // of trunc.
+    SkScalar v = x + 0.5f;
+    // Produce the top or left offset a value on the range [0, 1).
+    SkScalar f = v - SkScalarTruncToScalar(v);
+    // Produce the filter value which is on the range (0, 1].
+    SkScalar r =  1.0f - f;
+    SkASSERT(0.0f < r && r <= 1.0f);
+    return r;
+}
+
+// -- BilerpSampler --------------------------------------------------------------------------------
+// BilerpSampler - use a bilerp filter to create runs of destination pixels.
+// Note: in the code below, there are two types of points
+//       * sample points - these are the points passed in by pointList* and Spans.
+//       * filter points - are created from a sample point to form the coordinates of the points
+//                         to use in the filter and to generate the filter values.
+template<typename Accessor, typename Next>
+class BilerpSampler : public SkLinearBitmapPipeline::SampleProcessorInterface {
+public:
+    template<typename... Args>
+    BilerpSampler(
+        SkLinearBitmapPipeline::BlendProcessorInterface* next,
+        SkISize dimensions,
+        SkShader::TileMode xTile, SkShader::TileMode yTile,
+        Args&& ... args
+    )
+        : fNext{next}
+        , fXEdgeType{xTile}
+        , fXMax{dimensions.width() - 1}
+        , fYEdgeType{yTile}
+        , fYMax{dimensions.height() - 1}
+        , fAccessor{std::forward<Args>(args)...} { }
+
+    BilerpSampler(SkLinearBitmapPipeline::BlendProcessorInterface* next,
+                   const BilerpSampler& sampler)
+        : fNext{next}
+        , fXEdgeType{sampler.fXEdgeType}
+        , fXMax{sampler.fXMax}
+        , fYEdgeType{sampler.fYEdgeType}
+        , fYMax{sampler.fYMax}
+        , fAccessor{sampler.fAccessor} { }
+
+    void SK_VECTORCALL pointListFew(int n, Sk4s xs, Sk4s ys) override {
+        SkASSERT(0 < n && n < 4);
+        auto bilerpPixel = [&](int index) {
+            return this->bilerpSamplePoint(SkPoint{xs[index], ys[index]});
+        };
+
+        if (n >= 1) fNext->blendPixel(bilerpPixel(0));
+        if (n >= 2) fNext->blendPixel(bilerpPixel(1));
+        if (n >= 3) fNext->blendPixel(bilerpPixel(2));
+    }
+
+    void SK_VECTORCALL pointList4(Sk4s xs, Sk4s ys) override {
+        auto bilerpPixel = [&](int index) {
+            return this->bilerpSamplePoint(SkPoint{xs[index], ys[index]});
+        };
+        fNext->blend4Pixels(bilerpPixel(0), bilerpPixel(1), bilerpPixel(2), bilerpPixel(3));
+    }
+
+    void pointSpan(Span span) override {
+        SkASSERT(!span.isEmpty());
+        SkPoint start;
+        SkScalar length;
+        int count;
+        std::tie(start, length, count) = span;
+
+        // Nothing to do.
+        if (count == 0) {
+            return;
+        }
+
+        // Trivial case. No sample points are generated other than start.
+        if (count == 1) {
+            fNext->blendPixel(this->bilerpSamplePoint(start));
+            return;
+        }
+
+        // Note: the following code could be done in terms of dx = length / (count -1), but that
+        // would introduce a divide that is not needed for the most common dx == 1 cases.
+        SkScalar absLength = SkScalarAbs(length);
+        if (absLength == 0.0f) {
+            // |dx| == 0
+            // length is zero, so clamp an edge pixel.
+            this->spanZeroRate(span);
+        } else if (absLength < (count - 1)) {
+            // 0 < |dx| < 1.
+            this->spanSlowRate(span);
+        } else if (absLength == (count - 1)) {
+            // |dx| == 1.
+            if (sample_to_filter(span.startX()) == 1.0f
+                && sample_to_filter(span.startY()) == 1.0f) {
+                // All the pixels are aligned with the dest; go fast.
+                src_strategy_blend(span, fNext, &fAccessor);
+            } else {
+                // There is some sub-pixel offsets, so bilerp.
+                this->spanUnitRate(span);
+            }
+        } else if (absLength < 2.0f * (count - 1)) {
+            // 1 < |dx| < 2.
+            this->spanMediumRate(span);
+        } else {
+            // |dx| >= 2.
+            this->spanFastRate(span);
+        }
+    }
+
+    void repeatSpan(Span span, int32_t repeatCount) override {
+        while (repeatCount > 0) {
+            this->pointSpan(span);
+            repeatCount--;
+        }
+    }
+
+private:
+
+    // Convert a sample point to the points used by the filter.
+    void filterPoints(SkPoint sample, Sk4i* filterXs, Sk4i* filterYs) {
+        // May be less than zero. Be careful to use Floor.
+        int x0 = adjust_edge(fXEdgeType, SkScalarFloorToInt(X(sample) - 0.5), fXMax);
+        // Always greater than zero. Use the faster Trunc.
+        int x1 = adjust_edge(fXEdgeType, SkScalarTruncToInt(X(sample) + 0.5), fXMax);
+        int y0 = adjust_edge(fYEdgeType, SkScalarFloorToInt(Y(sample) - 0.5), fYMax);
+        int y1 = adjust_edge(fYEdgeType, SkScalarTruncToInt(Y(sample) + 0.5), fYMax);
+
+        *filterXs = Sk4i{x0, x1, x0, x1};
+        *filterYs = Sk4i{y0, y0, y1, y1};
+    }
+
+    // Given a sample point, generate a color by bilerping the four filter points.
+    Sk4f bilerpSamplePoint(SkPoint sample) {
+        Sk4i iXs, iYs;
+        filterPoints(sample, &iXs, &iYs);
+        Sk4f px00, px10, px01, px11;
+        fAccessor.get4Pixels(iXs, iYs, &px00, &px10, &px01, &px11);
+        return bilerp4(Sk4f{X(sample) - 0.5f}, Sk4f{Y(sample) - 0.5f}, px00, px10, px01, px11);
+    }
+
+    // Get two pixels at x from row0 and row1.
+    void get2PixelColumn(const void* row0, const void* row1, int x, Sk4f* px0, Sk4f* px1) {
+        *px0 = fAccessor.getPixelFromRow(row0, x);
+        *px1 = fAccessor.getPixelFromRow(row1, x);
+    }
+
+    // |dx| == 0. This code assumes that length is zero.
+    void spanZeroRate(Span span) {
+        SkPoint start; SkScalar length; int count;
+        std::tie(start, length, count) = span;
+        SkASSERT(length == 0.0f);
+
+        // Filter for the blending of the top and bottom pixels.
+        SkScalar filterY = sample_to_filter(Y(start));
+
+        // Generate the four filter points from the sample point start. Generate the row* values.
+        Sk4i iXs, iYs;
+        this->filterPoints(start, &iXs, &iYs);
+        const void* const row0 = fAccessor.row(iYs[0]);
+        const void* const row1 = fAccessor.row(iYs[2]);
+
+        // Get the two pixels that make up the clamping pixel.
+        Sk4f pxTop, pxBottom;
+        this->get2PixelColumn(row0, row1, SkScalarFloorToInt(X(start)), &pxTop, &pxBottom);
+        Sk4f pixel = pxTop * filterY + (1.0f - filterY) * pxBottom;
+
+        while (count >= 4) {
+            fNext->blend4Pixels(pixel, pixel, pixel, pixel);
+            count -= 4;
+        }
+        while (count > 0) {
+            fNext->blendPixel(pixel);
+            count -= 1;
+        }
+    }
+
+    // 0 < |dx| < 1. This code reuses the calculations from previous pixels to reduce
+    // computation. In particular, several destination pixels maybe generated from the same four
+    // source pixels.
+    // In the following code a "part" is a combination of two pixels from the same column of the
+    // filter.
+    void spanSlowRate(Span span) {
+        SkPoint start; SkScalar length; int count;
+        std::tie(start, length, count) = span;
+
+        // Calculate the distance between each sample point.
+        const SkScalar dx = length / (count - 1);
+        SkASSERT(-1.0f < dx && dx < 1.0f && dx != 0.0f);
+
+        // Generate the filter values for the top-left corner.
+        // Note: these values are in filter space; this has implications about how to adjust
+        // these values at each step. For example, as the sample point increases, the filter
+        // value decreases, this is because the filter and position are related by
+        // (1 - (X(sample) - .5)) % 1. The (1 - stuff) causes the filter to move in the opposite
+        // direction of the sample point which is increasing by dx.
+        SkScalar filterX = sample_to_filter(X(start));
+        SkScalar filterY = sample_to_filter(Y(start));
+
+        // Generate the four filter points from the sample point start. Generate the row* values.
+        Sk4i iXs, iYs;
+        this->filterPoints(start, &iXs, &iYs);
+        const void* const row0 = fAccessor.row(iYs[0]);
+        const void* const row1 = fAccessor.row(iYs[2]);
+
+        // Generate part of the filter value at xColumn.
+        auto partAtColumn = [&](int xColumn) {
+            int adjustedColumn = adjust_edge(fXEdgeType, xColumn, fXMax);
+            Sk4f pxTop, pxBottom;
+            this->get2PixelColumn(row0, row1, adjustedColumn, &pxTop, &pxBottom);
+            return pxTop * filterY + (1.0f - filterY) * pxBottom;
+        };
+
+        // The leftPart is made up of two pixels from the left column of the filter, right part
+        // is similar. The top and bottom pixels in the *Part are created as a linear blend of
+        // the top and bottom pixels using filterY. See the partAtColumn function above.
+        Sk4f leftPart  = partAtColumn(iXs[0]);
+        Sk4f rightPart = partAtColumn(iXs[1]);
+
+        // Create a destination color by blending together a left and right part using filterX.
+        auto bilerp = [&](const Sk4f& leftPart, const Sk4f& rightPart) {
+            Sk4f pixel = leftPart * filterX + rightPart * (1.0f - filterX);
+            return check_pixel(pixel);
+        };
+
+        // Send the first pixel to the destination. This simplifies the loop structure so that no
+        // extra pixels are fetched for the last iteration of the loop.
+        fNext->blendPixel(bilerp(leftPart, rightPart));
+        count -= 1;
+
+        if (dx > 0.0f) {
+            // * positive direction - generate destination pixels by sliding the filter from left
+            //                        to right.
+            int rightPartCursor = iXs[1];
+
+            // Advance the filter from left to right. Remember that moving the top-left corner of
+            // the filter to the right actually makes the filter value smaller.
+            auto advanceFilter = [&]() {
+                filterX -= dx;
+                if (filterX <= 0.0f) {
+                    filterX += 1.0f;
+                    leftPart = rightPart;
+                    rightPartCursor += 1;
+                    rightPart = partAtColumn(rightPartCursor);
+                }
+                SkASSERT(0.0f < filterX && filterX <= 1.0f);
+
+                return bilerp(leftPart, rightPart);
+            };
+
+            while (count >= 4) {
+                Sk4f px0 = advanceFilter(),
+                     px1 = advanceFilter(),
+                     px2 = advanceFilter(),
+                     px3 = advanceFilter();
+                fNext->blend4Pixels(px0, px1, px2, px3);
+                count -= 4;
+            }
+
+            while (count > 0) {
+                fNext->blendPixel(advanceFilter());
+                count -= 1;
+            }
+        } else {
+            // * negative direction - generate destination pixels by sliding the filter from
+            //                        right to left.
+            int leftPartCursor = iXs[0];
+
+            // Advance the filter from right to left. Remember that moving the top-left corner of
+            // the filter to the left actually makes the filter value larger.
+            auto advanceFilter = [&]() {
+                // Remember, dx < 0 therefore this adds |dx| to filterX.
+                filterX -= dx;
+                // At this point filterX may be > 1, and needs to be wrapped back on to the filter
+                // interval, and the next column in the filter is calculated.
+                if (filterX > 1.0f) {
+                    filterX -= 1.0f;
+                    rightPart = leftPart;
+                    leftPartCursor -= 1;
+                    leftPart = partAtColumn(leftPartCursor);
+                }
+                SkASSERT(0.0f < filterX && filterX <= 1.0f);
+
+                return bilerp(leftPart, rightPart);
+            };
+
+            while (count >= 4) {
+                Sk4f px0 = advanceFilter(),
+                     px1 = advanceFilter(),
+                     px2 = advanceFilter(),
+                     px3 = advanceFilter();
+                fNext->blend4Pixels(px0, px1, px2, px3);
+                count -= 4;
+            }
+
+            while (count > 0) {
+                fNext->blendPixel(advanceFilter());
+                count -= 1;
+            }
+        }
+    }
+
+    // |dx| == 1. Moving through source space at a rate of 1 source pixel per 1 dst pixel.
+    // Every filter part is used for two destination pixels, and the code can bulk load four
+    // pixels at a time.
+    void spanUnitRate(Span span) {
+        SkPoint start; SkScalar length; int count;
+        std::tie(start, length, count) = span;
+        SkASSERT(SkScalarAbs(length) == (count - 1));
+
+        // Calculate the four filter points of start, and use the two different Y values to
+        // generate the row pointers.
+        Sk4i iXs, iYs;
+        filterPoints(start, &iXs, &iYs);
+        const void* row0 = fAccessor.row(iYs[0]);
+        const void* row1 = fAccessor.row(iYs[2]);
+
+        // Calculate the filter values for the top-left filter element.
+        const SkScalar filterX = sample_to_filter(X(start));
+        const SkScalar filterY = sample_to_filter(Y(start));
+
+        // Generate part of the filter value at xColumn.
+        auto partAtColumn = [&](int xColumn) {
+            int adjustedColumn = adjust_edge(fXEdgeType, xColumn, fXMax);
+            Sk4f pxTop, pxBottom;
+            this->get2PixelColumn(row0, row1, adjustedColumn, &pxTop, &pxBottom);
+            return pxTop * filterY + (1.0f - filterY) * pxBottom;
+        };
+
+        auto get4Parts = [&](int ix, Sk4f* part0, Sk4f* part1, Sk4f* part2, Sk4f* part3) {
+            // Check if the pixels needed are near the edges. If not go fast using bulk pixels,
+            // otherwise be careful.
+            if (0 <= ix && ix <= fXMax - 3) {
+                Sk4f px00, px10, px20, px30,
+                     px01, px11, px21, px31;
+                fAccessor.get4Pixels(row0, ix, &px00, &px10, &px20, &px30);
+                fAccessor.get4Pixels(row1, ix, &px01, &px11, &px21, &px31);
+                *part0 = filterY * px00 + (1.0f - filterY) * px01;
+                *part1 = filterY * px10 + (1.0f - filterY) * px11;
+                *part2 = filterY * px20 + (1.0f - filterY) * px21;
+                *part3 = filterY * px30 + (1.0f - filterY) * px31;
+            } else {
+                *part0 = partAtColumn(ix + 0);
+                *part1 = partAtColumn(ix + 1);
+                *part2 = partAtColumn(ix + 2);
+                *part3 = partAtColumn(ix + 3);
+            }
+        };
+
+        auto bilerp = [&](const Sk4f& part0, const Sk4f& part1) {
+            return part0 * filterX + part1 * (1.0f - filterX);
+        };
+
+        if (length > 0) {
+            // * positive direction - generate destination pixels by sliding the filter from left
+            //                        to right.
+
+            // overlapPart is the filter part from the end of the previous four pixels used at
+            // the start of the next four pixels.
+            Sk4f overlapPart = partAtColumn(iXs[0]);
+            int rightColumnCursor = iXs[1];
+            while (count >= 4) {
+                Sk4f part0, part1, part2, part3;
+                get4Parts(rightColumnCursor, &part0, &part1, &part2, &part3);
+                Sk4f px0 = bilerp(overlapPart, part0);
+                Sk4f px1 = bilerp(part0, part1);
+                Sk4f px2 = bilerp(part1, part2);
+                Sk4f px3 = bilerp(part2, part3);
+                overlapPart = part3;
+                fNext->blend4Pixels(px0, px1, px2, px3);
+                rightColumnCursor += 4;
+                count -= 4;
+            }
+
+            while (count > 0) {
+                Sk4f rightPart = partAtColumn(rightColumnCursor);
+
+                fNext->blendPixel(bilerp(overlapPart, rightPart));
+                overlapPart = rightPart;
+                rightColumnCursor += 1;
+                count -= 1;
+            }
+        } else {
+            // * negative direction - generate destination pixels by sliding the filter from
+            //                        right to left.
+            Sk4f overlapPart = partAtColumn(iXs[1]);
+            int leftColumnCursor = iXs[0];
+
+            while (count >= 4) {
+                Sk4f part0, part1, part2, part3;
+                get4Parts(leftColumnCursor - 3, &part3, &part2, &part1, &part0);
+                Sk4f px0 = bilerp(part0, overlapPart);
+                Sk4f px1 = bilerp(part1, part0);
+                Sk4f px2 = bilerp(part2, part1);
+                Sk4f px3 = bilerp(part3, part2);
+                overlapPart = part3;
+                fNext->blend4Pixels(px0, px1, px2, px3);
+                leftColumnCursor -= 4;
+                count -= 4;
+            }
+
+            while (count > 0) {
+                Sk4f leftPart = partAtColumn(leftColumnCursor);
+
+                fNext->blendPixel(bilerp(leftPart, overlapPart));
+                overlapPart = leftPart;
+                leftColumnCursor -= 1;
+                count -= 1;
+            }
+        }
+    }
+
+    // 1 < |dx| < 2. Going through the source pixels at a faster rate than the dest pixels, but
+    // still slow enough to take advantage of previous calculations.
+    void spanMediumRate(Span span) {
+        SkPoint start; SkScalar length; int count;
+        std::tie(start, length, count) = span;
+
+        // Calculate the distance between each sample point.
+        const SkScalar dx = length / (count - 1);
+        SkASSERT((-2.0f < dx && dx < -1.0f) || (1.0f < dx && dx < 2.0f));
+
+        // Generate the filter values for the top-left corner.
+        // Note: these values are in filter space; this has implications about how to adjust
+        // these values at each step. For example, as the sample point increases, the filter
+        // value decreases, this is because the filter and position are related by
+        // (1 - (X(sample) - .5)) % 1. The (1 - stuff) causes the filter to move in the opposite
+        // direction of the sample point which is increasing by dx.
+        SkScalar filterX = sample_to_filter(X(start));
+        SkScalar filterY = sample_to_filter(Y(start));
+
+        // Generate the four filter points from the sample point start. Generate the row* values.
+        Sk4i iXs, iYs;
+        this->filterPoints(start, &iXs, &iYs);
+        const void* const row0 = fAccessor.row(iYs[0]);
+        const void* const row1 = fAccessor.row(iYs[2]);
+
+        // Generate part of the filter value at xColumn.
+        auto partAtColumn = [&](int xColumn) {
+            int adjustedColumn = adjust_edge(fXEdgeType, xColumn, fXMax);
+            Sk4f pxTop, pxBottom;
+            this->get2PixelColumn(row0, row1, adjustedColumn, &pxTop, &pxBottom);
+            return pxTop * filterY + (1.0f - filterY) * pxBottom;
+        };
+
+        // The leftPart is made up of two pixels from the left column of the filter, right part
+        // is similar. The top and bottom pixels in the *Part are created as a linear blend of
+        // the top and bottom pixels using filterY. See the nextPart function below.
+        Sk4f leftPart  = partAtColumn(iXs[0]);
+        Sk4f rightPart = partAtColumn(iXs[1]);
+
+        // Create a destination color by blending together a left and right part using filterX.
+        auto bilerp = [&](const Sk4f& leftPart, const Sk4f& rightPart) {
+            Sk4f pixel = leftPart * filterX + rightPart * (1.0f - filterX);
+            return check_pixel(pixel);
+        };
+
+        // Send the first pixel to the destination. This simplifies the loop structure so that no
+        // extra pixels are fetched for the last iteration of the loop.
+        fNext->blendPixel(bilerp(leftPart, rightPart));
+        count -= 1;
+
+        if (dx > 0.0f) {
+            // * positive direction - generate destination pixels by sliding the filter from left
+            //                        to right.
+            int rightPartCursor = iXs[1];
+
+            // Advance the filter from left to right. Remember that moving the top-left corner of
+            // the filter to the right actually makes the filter value smaller.
+            auto advanceFilter = [&]() {
+                filterX -= dx;
+                // At this point filterX is less than zero, but might actually be less than -1.
+                if (filterX > -1.0f) {
+                    filterX += 1.0f;
+                    leftPart = rightPart;
+                    rightPartCursor += 1;
+                    rightPart = partAtColumn(rightPartCursor);
+                } else {
+                    filterX += 2.0f;
+                    rightPartCursor += 2;
+                    leftPart = partAtColumn(rightPartCursor - 1);
+                    rightPart = partAtColumn(rightPartCursor);
+                }
+                SkASSERT(0.0f < filterX && filterX <= 1.0f);
+
+                return bilerp(leftPart, rightPart);
+            };
+
+            while (count >= 4) {
+                Sk4f px0 = advanceFilter(),
+                     px1 = advanceFilter(),
+                     px2 = advanceFilter(),
+                     px3 = advanceFilter();
+                fNext->blend4Pixels(px0, px1, px2, px3);
+                count -= 4;
+            }
+
+            while (count > 0) {
+                fNext->blendPixel(advanceFilter());
+                count -= 1;
+            }
+        } else {
+            // * negative direction - generate destination pixels by sliding the filter from
+            //                        right to left.
+            int leftPartCursor = iXs[0];
+
+            auto advanceFilter = [&]() {
+                // Remember, dx < 0 therefore this adds |dx| to filterX.
+                filterX -= dx;
+                // At this point, filterX is greater than one, but may actually be greater than two.
+                if (filterX < 2.0f) {
+                    filterX -= 1.0f;
+                    rightPart = leftPart;
+                    leftPartCursor -= 1;
+                    leftPart = partAtColumn(leftPartCursor);
+                } else {
+                    filterX -= 2.0f;
+                    leftPartCursor -= 2;
+                    rightPart = partAtColumn(leftPartCursor - 1);
+                    leftPart = partAtColumn(leftPartCursor);
+                }
+                SkASSERT(0.0f < filterX && filterX <= 1.0f);
+                return bilerp(leftPart, rightPart);
+            };
+
+            while (count >= 4) {
+                Sk4f px0 = advanceFilter(),
+                     px1 = advanceFilter(),
+                     px2 = advanceFilter(),
+                     px3 = advanceFilter();
+                fNext->blend4Pixels(px0, px1, px2, px3);
+                count -= 4;
+            }
+
+            while (count > 0) {
+                fNext->blendPixel(advanceFilter());
+                count -= 1;
+            }
+        }
+    }
+
+    // We're moving through source space faster than dst (zoomed out),
+    // so we'll never reuse a source pixel or be able to do contiguous loads.
+    void spanFastRate(Span span) {
+        SkPoint start; SkScalar length; int count;
+        std::tie(start, length, count) = span;
+        SkScalar x = X(start);
+        SkScalar y = Y(start);
+
+        SkScalar dx = length / (count - 1);
+        while (count > 0) {
+            fNext->blendPixel(this->bilerpSamplePoint(SkPoint{x, y}));
+            x += dx;
+            count -= 1;
+        }
+    }
+
+    Next* const              fNext;
+    const SkShader::TileMode fXEdgeType;
+    const int                fXMax;
+    const SkShader::TileMode fYEdgeType;
+    const int                fYMax;
+    Accessor                 fAccessor;
+};
+
+}  // namespace
+
+#endif  // SkLinearBitmapPipeline_sampler_DEFINED