Add point spans, but fall back for all cases.

src/core/SkLinearBitmapPipeline.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkLinearBitmapPipeline.h"
 #include "SkPM4f.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 #include "SkColor.h"
 #include "SkSize.h"
 
 struct X {
     explicit X(SkScalar val) : fVal{val} { }
-    explicit X(SkPoint pt) : fVal{pt.fX} { }
-    explicit X(SkSize s) : fVal{s.fWidth} { }
-    explicit X(SkISize s) : fVal(s.fWidth) { }
+    explicit X(SkPoint pt)   : fVal{pt.fX} { }
+    explicit X(SkSize s)     : fVal{s.fWidth} { }
+    explicit X(SkISize s)    : fVal(s.fWidth) { }
     operator float () const {return fVal;}
 private:
     float fVal;
 };
 
 struct Y {
     explicit Y(SkScalar val) : fVal{val} { }
-    explicit Y(SkPoint pt) : fVal{pt.fY} { }
-    explicit Y(SkSize s) : fVal{s.fHeight} { }
-    explicit Y(SkISize s) : fVal(s.fHeight) { }
+    explicit Y(SkPoint pt)   : fVal{pt.fY} { }
+    explicit Y(SkSize s)     : fVal{s.fHeight} { }
+    explicit Y(SkISize s)    : fVal(s.fHeight) { }
     operator float () const {return fVal;}
 private:
     float fVal;
 };
 
+template <typename Stage>
+void span_fallback(SkPoint start, SkScalar length, int count, Stage* stage) {
+    // If count == 1 use PointListFew instead.
+    SkASSERT(count > 1);
+
+    float dx = length / (count - 1);
+    Sk4f Xs = Sk4f(X(start)) + Sk4f{0.0f, 1.0f, 2.0f, 3.0f} * Sk4f{dx};
+    Sk4f Ys{Y(start)};
+    Sk4f fourDx = {4.0f * dx};
+
+    while (count >= 4) {
+        stage->pointList4(Xs, Ys);
+        Xs = Xs + fourDx;
+        count -= 4;
+    }
+    if (count > 0) {
+        stage->pointListFew(count, Xs, Ys);
+    }
+}
+
 template<typename Strategy, typename Next>
 class PointProcessor final : public PointProcessorInterface {
 public:
     template <typename... Args>
     PointProcessor(Next* next, Args&&... args)
         : fNext{next}
         , fStrategy{std::forward<Args>(args)...}{ }
 
     void pointListFew(int n, Sk4fArg xs, Sk4fArg ys) override {
         Sk4f newXs = xs;
         Sk4f newYs = ys;
         fStrategy.processPoints(&newXs, &newYs);
         fNext->pointListFew(n, newXs, newYs);
     }
 
     void pointList4(Sk4fArg xs, Sk4fArg ys) override {
         Sk4f newXs = xs;
         Sk4f newYs = ys;
         fStrategy.processPoints(&newXs, &newYs);
         fNext->pointList4(newXs, newYs);
     }
 
+    void pointSpan(SkPoint start, SkScalar length, int count) override {
+        span_fallback(start, length, count, this);
+    }
+
 private:
     Next* const fNext;
     Strategy fStrategy;
 };
 
 template<typename Strategy, typename Next>
 class BilerpProcessor final : public BilerpProcessorInterface  {
 public:
     template <typename... Args>
     BilerpProcessor(Next* next, Args&&... args)
@@ skipping 14 matching lines @@
         fNext->pointList4(newXs, newYs);
     }
 
     void bilerpList(Sk4fArg xs, Sk4fArg ys) override {
         Sk4f newXs = xs;
         Sk4f newYs = ys;
         fStrategy.processPoints(&newXs, &newYs);
         fNext->bilerpList(newXs, newYs);
     }
 
+    void pointSpan(SkPoint start, SkScalar length, int count) override {
+        span_fallback(start, length, count, this);
+    }
+
 private:
     Next* const fNext;
     Strategy fStrategy;
 };
 
 class SkippedStage final : public BilerpProcessorInterface {
     void pointListFew(int n, Sk4fArg xs, Sk4fArg ys) override {
         SkFAIL("Skipped stage.");
     }
     void pointList4(Sk4fArg Xs, Sk4fArg Ys) override {
         SkFAIL("Skipped stage.");
     }
-    virtual void bilerpList(Sk4fArg xs, Sk4fArg ys) override {
+    void bilerpList(Sk4fArg xs, Sk4fArg ys) override {
+        SkFAIL("Skipped stage.");
+    }
+    void pointSpan(SkPoint start, SkScalar length, int count) override {
         SkFAIL("Skipped stage.");
     }
 };
 
 class TranslateMatrixStrategy {
 public:
     TranslateMatrixStrategy(SkVector offset)
         : fXOffset{X(offset)}
         , fYOffset{Y(offset)} { }
     void processPoints(Sk4f* xs, Sk4f* ys) {
@@ skipping 92 matching lines @@
     void pointList4(Sk4fArg xs, Sk4fArg ys) override {
         //                    px00   px10   px01  px11
         const Sk4f kXOffsets{-0.5f,  0.5f, -0.5f, 0.5f},
                    kYOffsets{-0.5f, -0.5f,  0.5f, 0.5f};
         fNext->bilerpList(Sk4f{xs[0]} + kXOffsets, Sk4f{ys[0]} + kYOffsets);
         fNext->bilerpList(Sk4f{xs[1]} + kXOffsets, Sk4f{ys[1]} + kYOffsets);
         fNext->bilerpList(Sk4f{xs[2]} + kXOffsets, Sk4f{ys[2]} + kYOffsets);
         fNext->bilerpList(Sk4f{xs[3]} + kXOffsets, Sk4f{ys[3]} + kYOffsets);
     }
 
+    void pointSpan(SkPoint start, SkScalar length, int count) override {
+        span_fallback(start, length, count, this);
+    }
+
 private:
     Next* const fNext;
 };
 
 static PointProcessorInterface* choose_filter(
     BilerpProcessorInterface* next,
     SkFilterQuality filterQuailty,
     SkLinearBitmapPipeline::FilterStage* filterProc) {
     if (SkFilterQuality::kNone_SkFilterQuality == filterQuailty) {
         filterProc->Initialize<SkippedStage>();
@@ skipping 220 matching lines @@
         fNext->place4Pixels(px0, px1, px2, px3);
     }
 
     void bilerpList(Sk4fArg xs, Sk4fArg ys) override {
         Sk4f px00, px10, px01, px11;
         fStrategy.get4Pixels(xs, ys, &px00, &px10, &px01, &px11);
         Sk4f pixel = bilerp4(xs, ys, px00, px10, px01, px11);
         fNext->placePixel(pixel);
     }
 
+    void pointSpan(SkPoint start, SkScalar length, int count) override {
+        span_fallback(start, length, count, this);
+    }
+
 private:
     PixelPlacerInterface* const fNext;
     SourceStrategy fStrategy;
 };
 
 static BilerpProcessorInterface* choose_pixel_sampler(
     PixelPlacerInterface* next,
     const SkPixmap& srcPixmap,
     SkLinearBitmapPipeline::SampleStage* sampleStage) {
     const SkImageInfo& imageInfo = srcPixmap.info();
@@ skipping 82 matching lines @@
     // identity matrix, the matrix stage is skipped, and the tilerStage is the first stage.
     auto placementStage = choose_pixel_placer(srcImageInfo.alphaType(), &fPixelStage);
     auto samplerStage   = choose_pixel_sampler(placementStage, srcPixmap, &fSampleStage);
     auto tilerStage     = choose_tiler(samplerStage, size, xTile, yTile, &fTileXOrBothStage,
                                        &fTileYStage);
     auto filterStage    = choose_filter(tilerStage, filterQuality, &fFilterStage);
     fFirstStage         = choose_matrix(filterStage, inverse, &fMatrixStage);
 }
 
 void SkLinearBitmapPipeline::shadeSpan4f(int x, int y, SkPM4f* dst, int count) {
+    SkASSERT(count > 0);
     fPixelStage->setDestination(dst);
-
-    Sk4f Xs = Sk4f(x) + Sk4f{0.5f, 1.5f, 2.5f, 3.5f};
-    Sk4f Ys(y);
-    Sk4f fours{4.0f};
-
-    while (count >= 4) {
-        fFirstStage->pointList4(Xs, Ys);
-        Xs = Xs + fours;
-        count -= 4;
-    }
-    if (count > 0) {
-        fFirstStage->pointListFew(count, Xs, Ys);
+    // Adjust points by 0.5, 0.5 to sample from the center of the pixels.
+    if (count == 1) {
+        fFirstStage->pointListFew(1, Sk4f{x + 0.5f}, Sk4f{y + 0.5f});
+    } else {
+        // The count and length arguments start out in a precise relation in order to keep the
+        // math correct through the different stages. Count is the number of pixel to produce.
+        // Since the code samples at pixel centers, length is the distance from the center of the
+        // first pixel to the center of the last pixel. This implies that length is count-1.
+        fFirstStage->pointSpan(SkPoint{x + 0.5f, y + 0.5f}, count - 1, count);
     }
 }