Fix bad scaling in TiledLayer

cc/resources/content_layer_updater.cc

Index: cc/resources/content_layer_updater.cc
diff --git a/cc/resources/content_layer_updater.cc b/cc/resources/content_layer_updater.cc
index 8bd90e9d5a174768abab9709b7a3928540a2eac7..f6469ff052ea3063d5127bb8eb407a3a3060c3b0 100644
--- a/cc/resources/content_layer_updater.cc
+++ b/cc/resources/content_layer_updater.cc
@@ -14,6 +14,7 @@
 #include "third_party/skia/include/core/SkScalar.h"
 #include "ui/gfx/rect_conversions.h"
 #include "ui/gfx/rect_f.h"
+#include "ui/gfx/skia_util.h"
 
 namespace cc {
 
@@ -25,7 +26,9 @@ ContentLayerUpdater::ContentLayerUpdater(
       layer_id_(layer_id),
       layer_is_opaque_(false),
       layer_fills_bounds_completely_(false),
-      painter_(painter.Pass()) {}
+      painter_(painter.Pass()),
+      background_color_(SK_ColorTRANSPARENT) {
+}
 
 ContentLayerUpdater::~ContentLayerUpdater() {}
 
@@ -35,27 +38,62 @@ void ContentLayerUpdater::set_rendering_stats_instrumentation(
 }
 
 void ContentLayerUpdater::PaintContents(SkCanvas* canvas,
-                                        const gfx::Rect& content_rect,
+                                        const gfx::Size& layer_content_size,
+                                        const gfx::Rect& paint_rect,
                                         float contents_width_scale,
                                         float contents_height_scale) {
   TRACE_EVENT0("cc", "ContentLayerUpdater::PaintContents");
   if (!canvas)
     return;
   canvas->save();
-  canvas->translate(SkFloatToScalar(-content_rect.x()),
-                    SkFloatToScalar(-content_rect.y()));
-
-  // The |canvas| backing should be sized to hold the |content_rect|.
-  DCHECK_EQ(content_rect.width(), canvas->getBaseLayerSize().width());
-  DCHECK_EQ(content_rect.height(), canvas->getBaseLayerSize().height());
+  canvas->translate(SkIntToScalar(-paint_rect.x()),
+                    SkIntToScalar(-paint_rect.y()));
+
+  // The |canvas| backing should be sized to hold the |paint_rect|.
+  DCHECK_EQ(paint_rect.width(), canvas->getBaseLayerSize().width());
+  DCHECK_EQ(paint_rect.height(), canvas->getBaseLayerSize().height());
+
+  const bool is_scaled =
+      contents_width_scale != 1.f || contents_height_scale != 1.f;
+
+  if (is_scaled && (layer_is_opaque_ || layer_fills_bounds_completely_)) {
+    // Even if completely covered, for rasterizations that touch the edge of the
+    // layer, we also need to raster the background color underneath the last
+    // texel (since the paint won't cover it).
+    //
+    // The final texel of content may only be partially covered by a
+    // rasterization; this rect represents the content rect that is fully
+    // covered by content.
+    const gfx::Rect layer_content_rect = gfx::Rect(layer_content_size);
+    gfx::Rect deflated_layer_content_rect = layer_content_rect;
+    deflated_layer_content_rect.Inset(0, 0, 1, 1);
+
+    if (!layer_content_rect.Contains(deflated_layer_content_rect)) {
+      // Drawing at most 1 x 1 x (canvas width + canvas height) texels is 2-3X
+      // faster than clearing, so special case this.
+      DCHECK_LE(paint_rect.right(), layer_content_rect.right());
+      DCHECK_LE(paint_rect.bottom(), layer_content_rect.bottom());
+      canvas->save();
+      canvas->clipRect(gfx::RectToSkRect(layer_content_rect),
+                       SkRegion::kReplace_Op);
+      canvas->clipRect(gfx::RectToSkRect(deflated_layer_content_rect),
+                       SkRegion::kDifference_Op);
+      canvas->drawColor(background_color_, SkXfermode::kSrc_Mode);
+      canvas->restore();
+    }
+  }
 
-  gfx::Rect layer_rect = content_rect;
-  if (contents_width_scale != 1.f || contents_height_scale != 1.f) {
+  gfx::Rect layer_rect;
+  if (is_scaled) {
     canvas->scale(SkFloatToScalar(contents_width_scale),
                   SkFloatToScalar(contents_height_scale));
 
+    // NOTE: this may go beyond the bounds of the layer, but that shouldn't
+    // cause problems (anything beyond the layer is clipped out).
     layer_rect = gfx::ScaleToEnclosingRect(
-        content_rect, 1.f / contents_width_scale, 1.f / contents_height_scale);
+        paint_rect, 1.f / contents_width_scale, 1.f / contents_height_scale);
+  } else {
+    layer_rect = paint_rect;
   }
 
   SkRect layer_sk_rect = SkRect::MakeXYWH(
@@ -73,7 +111,7 @@ void ContentLayerUpdater::PaintContents(SkCanvas* canvas,
   painter_->Paint(canvas, layer_rect);
   canvas->restore();
 
-  content_rect_ = content_rect;
+  paint_rect_ = paint_rect;
 }
 
 void ContentLayerUpdater::SetOpaque(bool opaque) {
@@ -84,4 +122,8 @@ void ContentLayerUpdater::SetFillsBoundsCompletely(bool fills_bounds) {
   layer_fills_bounds_completely_ = fills_bounds;
 }
 
+void ContentLayerUpdater::SetBackgroundColor(SkColor background_color) {
+  background_color_ = background_color;
+}
+
 }  // namespace cc