SkBitmapProcState rounding bias

gm/imagescalealigned.cpp

 /*
  * Copyright 2015 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 "SkImage.h"
@@ skipping 16 matching lines @@
            set.fImages.push_back().reset(MakeImage(vectors[i], SK_ColorGREEN));
            set.fScales.push_back() = 1;
         }
     }
 
     SkString onShortName() override {
         return SkString("image_scale_aligned");
     }
 
     SkISize onISize() override {
-        return SkISize::Make(550, 300);
+        return SkISize::Make(580, 780);
     }
 
     void onDraw(SkCanvas* canvas) override {
         struct {
             SkPoint offset;
-            SkScalar scale;
+            SkVector scale;
         } cfgs[] = {
-            { {  10,    10    }, 1 },
-            { { 140.5f, 10    }, 1 },
-            { {  10,    80.5f }, 1 },
-            { { 140.5f, 80.5f }, 1 },
+            {{  10,    10    }, { 1, 1 }},
+            {{ 300.5f, 10    }, { 1, 1 }},
+            {{  10,    200.5f }, { 1, 1 }},
+            {{ 300.5f, 200.5f }, { 1, 1 }},
 
-            { { 280.49f, 10.49f }, 1 },
-            { { 410.51f, 10.49f }, 1 },
-            { { 280.49f, 80.51f }, 1 },
-            { { 410.51f, 80.51f }, 1 },
-
-            { {  10,    170    }, 1.1f },
-            { { 140.5f, 170    }, 1.1f },
-            { {  10,    240.5f }, 1.1f },
-            { { 140.5f, 240.5f }, 1.1f },
-
-            { { 280.49f, 170.49f }, 1.1f },
-            { { 410.51f, 170.49f }, 1.1f },
-            { { 280.49f, 240.51f }, 1.1f },
-            { { 410.51f, 240.51f }, 1.1f },
+            {{  10.5f, 400.5f }, {  1,  1 }},
+            {{ 550.5f, 400.5f }, { -1,  1 }},
+            {{  10.5f, 750.5f }, {  1, -1 }},
+            {{ 550.5f, 750.5f }, { -1, -1 }},
         };
 
         for (size_t i = 0; i < SK_ARRAY_COUNT(cfgs); ++i) {
             SkAutoCanvasRestore acr(canvas, true);
             canvas->translate(cfgs[i].offset.x(), cfgs[i].offset.y());
-            canvas->scale(cfgs[i].scale, cfgs[i].scale);
+            canvas->scale(cfgs[i].scale.x(), cfgs[i].scale.y());
             drawSets(canvas);
         }
     }
 
 private:
     struct ImageSet {
         SkSTArray<3, SkAutoTUnref<SkImage>, true> fImages;
         SkSTArray<3, SkScalar>                    fScales;
         SkVector                                  fVector;
     };
 
     static SkImage* MakeImage(const SkVector& vec, SkColor color) {
         const SkPoint start = SkPoint::Make(vec.y() * kSegLen / 2, vec.x() * kSegLen / 2);
         const SkPoint end   = SkPoint::Make(start.x() + vec.x() * (kSegLen - 1),
                                             start.y() + vec.y() * (kSegLen - 1));
 
         SkAutoTUnref<SkSurface> surface(SkSurface::NewRasterN32Premul(kSegLen, kSegLen));
         surface->getCanvas()->clear(SK_ColorTRANSPARENT);
 
         SkPaint paint;
         paint.setAntiAlias(true);
+        const SkRect border = SkRect::MakeIWH(kSegLen, kSegLen).makeInset(.5f, .5f);
+        paint.setColor(SK_ColorBLUE);
+        paint.setStyle(SkPaint::kStroke_Style);
+        surface->getCanvas()->drawRect(border, paint);
+
         paint.setColor(SK_ColorBLACK);
         surface->getCanvas()->drawLine(start.x(), start.y(), end.x(), end.y(), paint);
         surface->getCanvas()->drawPoint(start.x(), start.y(), color);
         surface->getCanvas()->drawPoint(end.x(), end.y(), color);
 
         return surface->newImageSnapshot();
     }
 
     void drawSets(SkCanvas* canvas) const {
         SkAutoCanvasRestore acr(canvas, true);
 
         const SkFilterQuality filters[] = {
             kNone_SkFilterQuality,
             kLow_SkFilterQuality,
             kMedium_SkFilterQuality,
             kHigh_SkFilterQuality
         };
         const bool AAs[] = { false, true };
 
         SkPaint paint;
         for (int i = 0; i < fSets.count(); ++i) {
             auto& set = fSets[i];
             SkPoint lastPt;
             for (size_t j = 0; j < SK_ARRAY_COUNT(AAs); ++j) {
                 paint.setAntiAlias(AAs[j]);
                 for (size_t k = 0; k < SK_ARRAY_COUNT(filters); ++k) {
                     paint.setFilterQuality(filters[k]);
                     lastPt = drawSet(canvas, set, paint);
-                    canvas->translate((kSegLen / 2) * set.fVector.y(),
-                                      (kSegLen / 2) * set.fVector.x());
+                    canvas->translate((kSegLen + 4) * set.fVector.y(),
+                                      (kSegLen + 4) * set.fVector.x());
                 }
             }
             canvas->translate(lastPt.x() + kSegLen,
-                - SkIntToScalar(kSegLen) / 2 * SK_ARRAY_COUNT(filters) * SK_ARRAY_COUNT(AAs));
+                - SkIntToScalar(kSegLen + 4) * SK_ARRAY_COUNT(filters) * SK_ARRAY_COUNT(AAs));
         }
     }
 
     SkPoint drawSet(SkCanvas* canvas, const ImageSet& set, const SkPaint& paint) const {
         SkASSERT(set.fImages.count() == set.fScales.count());
 
         SkPoint pt = SkPoint::Make(0, 0);
         for (int i = 0; i < set.fImages.count(); ++i) {
             auto& img = set.fImages[i];
             const SkRect dst =
                 SkRect::MakeXYWH(pt.x(), pt.y(),
                     img->width() * (1 + (set.fScales[i] - 1) * set.fVector.x()),
                     img->height() * (1 + (set.fScales[i] - 1) * set.fVector.y()));
 
             canvas->drawImageRect(img, dst, &paint);
             pt.offset(dst.width() * set.fVector.x(), dst.height() * set.fVector.y());
         }
 
         return pt;
     }
 
-    static const unsigned  kSegLen = 9;
-    static const unsigned  kStretchFactor = 2;
+    static const unsigned  kSegLen = 15;
+    static const unsigned  kStretchFactor = 4;
     SkSTArray<2, ImageSet> fSets;
 
     typedef GM INHERITED;
 };
 
 DEF_GM(return new ImageScaleAlignedGM();)