Splitting of layers for correct intersections

cc/output/software_renderer.cc

Index: cc/output/software_renderer.cc
diff --git a/cc/output/software_renderer.cc b/cc/output/software_renderer.cc
index 6571c33db12d478e375b31a626a64d8586cdc5b2..850a19c201b3da1be12f22fc8b635972bfaae5a1 100644
--- a/cc/output/software_renderer.cc
+++ b/cc/output/software_renderer.cc
@@ -26,6 +26,7 @@
 #include "third_party/skia/include/core/SkColor.h"
 #include "third_party/skia/include/core/SkImageFilter.h"
 #include "third_party/skia/include/core/SkMatrix.h"
+#include "third_party/skia/include/core/SkPoint.h"
 #include "third_party/skia/include/core/SkShader.h"
 #include "third_party/skia/include/effects/SkLayerRasterizer.h"
 #include "ui/gfx/geometry/rect_conversions.h"
@@ -184,6 +185,7 @@ void SoftwareRenderer::SetClipRect(const gfx::Rect& rect) {
   current_canvas_->resetMatrix();
   current_canvas_->clipRect(gfx::RectToSkRect(rect), SkRegion::kReplace_Op);
   current_canvas_->setMatrix(current_matrix);
+  current_canvas_->save(); //TODO(awoloszyn) this seems fishy.
 }
 
 void SoftwareRenderer::ClearCanvas(SkColor color) {
@@ -229,7 +231,13 @@ bool SoftwareRenderer::IsSoftwareResource(
   return false;
 }
 
-void SoftwareRenderer::DoDrawQuad(DrawingFrame* frame, const DrawQuad* quad) {
+void SoftwareRenderer::DoDrawQuad(DrawingFrame* frame,
+                                  const DrawQuad* quad,
+                                  const gfx::QuadF* draw_region) {
+  if (draw_region) {
+    current_canvas_->save();
+  }
+
   TRACE_EVENT0("cc", "SoftwareRenderer::DoDrawQuad");
   gfx::Transform quad_rect_matrix;
   QuadRectTransform(&quad_rect_matrix, quad->quadTransform(), quad->rect);
@@ -262,9 +270,31 @@ void SoftwareRenderer::DoDrawQuad(DrawingFrame* frame, const DrawQuad* quad) {
     current_paint_.setXfermodeMode(SkXfermode::kSrc_Mode);
   }
 
+  if (draw_region) {
+    gfx::QuadF local_draw_region(*draw_region);
+    SkPath draw_region_clip_path;
+    local_draw_region -=
+        gfx::Vector2dF(quad->visible_rect.x(), quad->visible_rect.y());
+    local_draw_region.Scale(1.0f / quad->visible_rect.width(),
+                            1.0f / quad->visible_rect.height());
+    local_draw_region -= gfx::Vector2dF(0.5f, 0.5f);
+
+    SkPoint clip_points[4];
+    QuadFToSkPoints(local_draw_region, clip_points);
+    draw_region_clip_path.addPoly(clip_points, 4, true);
+
+    current_canvas_->clipPath(
+        draw_region_clip_path, SkRegion::kIntersect_Op, false);
+  }
+
   switch (quad->material) {
     case DrawQuad::CHECKERBOARD:
-      DrawCheckerboardQuad(frame, CheckerboardDrawQuad::MaterialCast(quad));
+      // TODO(thildebr) For now since checkerboards shouldn't be part of a 3D
+      // context, clipping regions aren't supported so we skip drawing them
+      // if this becomes the case.
+      if (!draw_region) {
+        DrawCheckerboardQuad(frame, CheckerboardDrawQuad::MaterialCast(quad));
+      }
       break;
     case DrawQuad::DEBUG_BORDER:
       DrawDebugBorderQuad(frame, DebugBorderDrawQuad::MaterialCast(quad));
@@ -299,6 +329,9 @@ void SoftwareRenderer::DoDrawQuad(DrawingFrame* frame, const DrawQuad* quad) {
   }
 
   current_canvas_->resetMatrix();
+  if (draw_region) {
+    current_canvas_->restore();
+  }
 }
 
 void SoftwareRenderer::DrawCheckerboardQuad(const DrawingFrame* frame,