Fix rounding rules for skia operations to work with non-integer scaling factors.

ui/gfx/image/image_skia_operations.cc

Index: ui/gfx/image/image_skia_operations.cc
diff --git a/ui/gfx/image/image_skia_operations.cc b/ui/gfx/image/image_skia_operations.cc
index 4b5612ea063bc1376556b58dee5e03e80b9ffe23..ec9fb47c67b29bb20ba700b88f81f5f989b76f18 100644
--- a/ui/gfx/image/image_skia_operations.cc
+++ b/ui/gfx/image/image_skia_operations.cc
@@ -14,6 +14,8 @@
 #include "ui/gfx/image/image_skia_rep.h"
 #include "ui/gfx/image/image_skia_source.h"
 #include "ui/gfx/insets.h"
+#include "ui/gfx/point.h"
+#include "ui/gfx/point_conversions.h"
 #include "ui/gfx/rect.h"
 #include "ui/gfx/rect_conversions.h"
 #include "ui/gfx/size.h"
@@ -24,6 +26,23 @@
 namespace gfx {
 namespace {
 
+gfx::Rect DIPToPixelBounds(gfx::Rect dip_bounds, float scale) {
+  return ToEnclosingRect(ScaleRect(dip_bounds, scale));
+}
+
+gfx::Size DIPToPixelSize(gfx::Size dip_size, float scale) {
+  return ToCeiledSize(ScaleSize(dip_size, scale));
+}
+
+ImageSkiaRep CropImageSkiaRep(ImageSkiaRep& source,
+                              gfx::Rect& bounds_in_pixel) {
+  SkBitmap result;
+  bool success = source.sk_bitmap().extractSubset(&result,
+      RectToSkIRect(bounds_in_pixel));
+  DCHECK(success);
+  return ImageSkiaRep(result, source.scale_factor());
+}
+
 // Returns an image rep for the ImageSkiaSource to return to visually indicate
 // an error.
 ImageSkiaRep GetErrorImageRep(ui::ScaleFactor scale_factor,
@@ -54,7 +73,11 @@ class BinaryImageSource : public gfx::ImageSkiaSource {
   virtual ImageSkiaRep GetImageForScale(ui::ScaleFactor scale_factor) OVERRIDE {
     ImageSkiaRep first_rep = first_.GetRepresentation(scale_factor);
     ImageSkiaRep second_rep = second_.GetRepresentation(scale_factor);
-    if (first_rep.pixel_size() != second_rep.pixel_size()) {
+    // Allow for maximum of 1 pixel mismatch due to rounding errors when using
+    // fractional scale factors.
+    int dw = first_rep.pixel_width() - second_rep.pixel_width();
+    int dh = first_rep.pixel_height() - second_rep.pixel_height();

[oshima, 2013/03/13 14:47:52]

drive-by question: where / in which process the rounding error is happening now?
Just curious and having a pointer
to such case in the comment would be helpful to understand
for those who need to touch this code later.

+    if (abs(dw) > 1 || abs(dh) > 1) {
       DCHECK_NE(first_rep.scale_factor(), second_rep.scale_factor());
       if (first_rep.scale_factor() == second_rep.scale_factor()) {
         LOG(ERROR) << "ImageSkiaRep size mismatch in " << source_name_;
@@ -63,9 +86,11 @@ class BinaryImageSource : public gfx::ImageSkiaSource {
       }
       first_rep = first_.GetRepresentation(ui::SCALE_FACTOR_100P);
       second_rep = second_.GetRepresentation(ui::SCALE_FACTOR_100P);
-      DCHECK_EQ(first_rep.pixel_width(), second_rep.pixel_width());
-      DCHECK_EQ(first_rep.pixel_height(), second_rep.pixel_height());
-      if (first_rep.pixel_size() != second_rep.pixel_size()) {
+      dw = first_rep.pixel_width() - second_rep.pixel_width();
+      dh = first_rep.pixel_height() - second_rep.pixel_height();
+      DCHECK_LE(abs(dw), 1);
+      DCHECK_LE(abs(dh), 1);
+      if (abs(dw) > 1 || abs(dh) > 1) {
         LOG(ERROR) << "ImageSkiaRep size mismatch in " << source_name_;
         return GetErrorImageRep(first_rep.scale_factor(),
                                 first_rep.pixel_size());
@@ -73,6 +98,12 @@ class BinaryImageSource : public gfx::ImageSkiaSource {
     } else {
       DCHECK_EQ(first_rep.scale_factor(), second_rep.scale_factor());
     }
+    if (dw || dh) {
+      gfx::Rect bounds = IntersectRects(Rect(first_rep.pixel_size()),
+                                        Rect(second_rep.pixel_size()));
+      first_rep = CropImageSkiaRep(first_rep, bounds);
+      second_rep = CropImageSkiaRep(second_rep, bounds);
+    }
     return CreateImageSkiaRep(first_rep, second_rep);
   }
 
@@ -216,10 +247,12 @@ class TiledImageSource : public gfx::ImageSkiaSource {
   virtual ImageSkiaRep GetImageForScale(ui::ScaleFactor scale_factor) OVERRIDE {
     ImageSkiaRep source_rep = source_.GetRepresentation(scale_factor);
     float scale = ui::GetScaleFactorScale(source_rep.scale_factor());
+    gfx::Rect bounds = DIPToPixelBounds(gfx::Rect(src_x_, src_y_, dst_w_,
+                                                  dst_h_), scale);
     return ImageSkiaRep(
         SkBitmapOperations::CreateTiledBitmap(
             source_rep.sk_bitmap(),
-            src_x_ * scale, src_y_ * scale, dst_w_ * scale, dst_h_ * scale),
+            bounds.x(), bounds.y(), bounds.width(), bounds.height()),
         source_rep.scale_factor());
   }
 
@@ -260,37 +293,30 @@ class HSLImageSource : public gfx::ImageSkiaSource {
 
 // ImageSkiaSource which uses SkBitmapOperations::CreateButtonBackground
 // to generate image reps for the target image.
-class ButtonImageSource: public gfx::ImageSkiaSource {
+class ButtonImageSource: public BinaryImageSource {
  public:
   ButtonImageSource(SkColor color,
                     const ImageSkia& image,
                     const ImageSkia& mask)
-      : color_(color),
-        image_(image),
-        mask_(mask) {
+      : BinaryImageSource(image, mask, "ButtonImageSource"),
+        color_(color) {
   }
 
   virtual ~ButtonImageSource() {
   }
 
-  // gfx::ImageSkiaSource overrides:
-  virtual ImageSkiaRep GetImageForScale(ui::ScaleFactor scale_factor) OVERRIDE {
-    ImageSkiaRep image_rep = image_.GetRepresentation(scale_factor);
-    ImageSkiaRep mask_rep = mask_.GetRepresentation(scale_factor);
-    if (image_rep.scale_factor() != mask_rep.scale_factor()) {
-      image_rep = image_.GetRepresentation(ui::SCALE_FACTOR_100P);
-      mask_rep = mask_.GetRepresentation(ui::SCALE_FACTOR_100P);
-    }
+  // BinaryImageSource overrides:
+  virtual ImageSkiaRep CreateImageSkiaRep(
+      const ImageSkiaRep& first_rep,
+      const ImageSkiaRep& second_rep) const OVERRIDE {
     return gfx::ImageSkiaRep(
         SkBitmapOperations::CreateButtonBackground(color_,
-              image_rep.sk_bitmap(), mask_rep.sk_bitmap()),
-          image_rep.scale_factor());
+              first_rep.sk_bitmap(), second_rep.sk_bitmap()),
+          first_rep.scale_factor());
   }
 
  private:
   const SkColor color_;
-  const ImageSkia image_;
-  const ImageSkia mask_;
 
   DISALLOW_COPY_AND_ASSIGN(ButtonImageSource);
 };
@@ -312,13 +338,9 @@ class ExtractSubsetImageSource: public gfx::ImageSkiaSource {
   virtual ImageSkiaRep GetImageForScale(ui::ScaleFactor scale_factor) OVERRIDE {
     ImageSkiaRep image_rep = image_.GetRepresentation(scale_factor);
     float scale_to_pixel = ui::GetScaleFactorScale(image_rep.scale_factor());
-    SkIRect subset_bounds_in_pixel = RectToSkIRect(ToFlooredRectDeprecated(
-        gfx::ScaleRect(subset_bounds_, scale_to_pixel)));
-    SkBitmap dst;
-    bool success = image_rep.sk_bitmap().extractSubset(&dst,
-                                                       subset_bounds_in_pixel);
-    DCHECK(success);
-    return gfx::ImageSkiaRep(dst, image_rep.scale_factor());
+    Rect subset_bounds_in_pixel = DIPToPixelBounds(subset_bounds_,
+                                                   scale_to_pixel);
+    return CropImageSkiaRep(image_rep, subset_bounds_in_pixel);
   }
 
  private:
@@ -349,8 +371,7 @@ class ResizeSource : public ImageSkiaSource {
       return image_rep;
 
     const float scale = ui::GetScaleFactorScale(scale_factor);
-    const Size target_pixel_size = gfx::ToFlooredSize(
-        gfx::ScaleSize(target_dip_size_, scale));
+    const Size target_pixel_size = DIPToPixelSize(target_dip_size_, scale);
     const SkBitmap resized = skia::ImageOperations::Resize(
         image_rep.sk_bitmap(),
         resize_method_,