Support for color-spaces with multi-stop (texture) gradients

gm/gamut.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 "gm.h"
 
 #include "SkSurface.h"
@@ skipping 40 matching lines @@
     const char* label() override {
         return fLabel.c_str();
     }
 protected:
     SkFilterQuality fQuality;
     SkBitmap        fBitmap;
     SkString        fLabel;
 };
 
 struct GradientCellRenderer : public CellRenderer {
-    GradientCellRenderer(SkColor colorOne, SkColor colorTwo) {
+    GradientCellRenderer(SkColor colorOne, SkColor colorTwo, bool manyStops) {
         fColors[0] = colorOne;
         fColors[1] = colorTwo;
+        fManyStops = manyStops;
     }
     void draw(SkCanvas* canvas) override {
         SkPoint points[2] = {
             SkPoint::Make(0, 0),
             SkPoint::Make(0, gScalarSize)
         };
         SkPaint paint;
-        paint.setShader(SkGradientShader::MakeLinear(points, fColors, nullptr, 2,
-                                                     SkShader::kClamp_TileMode));
+        if (fManyStops) {
+            SkColor colors[4] ={
+                fColors[0], fColors[0], fColors[1], fColors[1]
+            };
+            paint.setShader(SkGradientShader::MakeLinear(points, colors, nullptr, 4,
+                                                         SkShader::kClamp_TileMode));
+        } else {
+            paint.setShader(SkGradientShader::MakeLinear(points, fColors, nullptr, 2,
+                                                         SkShader::kClamp_TileMode));
+        }
         canvas->drawPaint(paint);
     }
     const char* label() override {
         return "Linear Gradient";
     }
 protected:
     SkColor fColors[2];
+    bool fManyStops;
 };
 
 struct VerticesCellRenderer : public CellRenderer {
     VerticesCellRenderer(SkColor colorOne, SkColor colorTwo) {
         fColors[0] = fColors[1] = colorOne;
         fColors[2] = fColors[3] = colorTwo;
     }
     void draw(SkCanvas* canvas) override {
         SkPaint paint;
         SkPoint vertices[4] = {
@@ skipping 101 matching lines @@
 
     // sRGB primaries, rendered as bitmaps
     renderers.push_back(new BitmapCellRenderer(SK_ColorRED, kNone_SkFilterQuality));
     renderers.push_back(new BitmapCellRenderer(SK_ColorGREEN, kLow_SkFilterQuality));
     // Larger bitmap to trigger mipmaps
     renderers.push_back(new BitmapCellRenderer(SK_ColorRED, kMedium_SkFilterQuality, 2.0f));
     // Smaller bitmap to trigger bicubic
     renderers.push_back(new BitmapCellRenderer(SK_ColorGREEN, kHigh_SkFilterQuality, 0.5f));
 
     // Various gradients involving sRGB primaries and white/black
-    renderers.push_back(new GradientCellRenderer(SK_ColorRED, SK_ColorGREEN));
-    renderers.push_back(new GradientCellRenderer(SK_ColorGREEN, SK_ColorBLACK));
-    renderers.push_back(new GradientCellRenderer(SK_ColorGREEN, SK_ColorWHITE));
+
+    // First with just two stops (implemented with uniforms on GPU)
+    renderers.push_back(new GradientCellRenderer(SK_ColorRED, SK_ColorGREEN, false));
+    renderers.push_back(new GradientCellRenderer(SK_ColorGREEN, SK_ColorBLACK, false));
+    renderers.push_back(new GradientCellRenderer(SK_ColorGREEN, SK_ColorWHITE, false));
+
+    // ... and then with four stops (implemented with textures on GPU)
+    renderers.push_back(new GradientCellRenderer(SK_ColorRED, SK_ColorGREEN, true));
+    renderers.push_back(new GradientCellRenderer(SK_ColorGREEN, SK_ColorBLACK, true));
+    renderers.push_back(new GradientCellRenderer(SK_ColorGREEN, SK_ColorWHITE, true));
 
     // Vertex colors
     renderers.push_back(new VerticesCellRenderer(SK_ColorRED, SK_ColorRED));
     renderers.push_back(new VerticesCellRenderer(SK_ColorRED, SK_ColorGREEN));
 
     draw_gamut_grid(canvas, renderers);
 }