Remove PerformClipping(),CanClipSelf() and the related logic in LTHCommon.

There is a precision lost issue for texture layers with CSS
transforms(Scaling) when applying TextureDrawQuad::PerformClipping()
to avoid explicitly setting a scissor. The rect is first divided by
the scale_factor, then round to integer value and finally multiplied
by the scale_factor in GLRenderer::EnqueueTextureQuad(). The round
process loses precision and the later scale operation enlarges the
error. This error leads to wrong width and height drawn and
introduces visual defects. 

BUG=240259

Review URL: https://codereview.chromium.org/24427006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227177 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 0 insertions, 74 deletions

diff --git a/cc/quads/texture_draw_quad.cc b/cc/quads/texture_draw_quad.cc
index ae7cfd6..191dcc4 100644
--- a/cc/quads/texture_draw_quad.cc
+++ b/cc/quads/texture_draw_quad.cc
@@ -84,80 +84,6 @@ const TextureDrawQuad* TextureDrawQuad::MaterialCast(const DrawQuad* quad) {
   return static_cast<const TextureDrawQuad*>(quad);
 }
 
-bool TextureDrawQuad::PerformClipping() {
-  // This only occurs if the rect is only scaled and translated (and thus still
-  // axis aligned).
-  if (!quadTransform().IsPositiveScaleOrTranslation())
-    return false;
-
-  // Grab our scale and make sure it's positive.
-  float x_scale = static_cast<float>(quadTransform().matrix().getDouble(0, 0));
-  float y_scale = static_cast<float>(quadTransform().matrix().getDouble(1, 1));
-
-  // Grab our offset.
-  gfx::Vector2dF offset(
-      static_cast<float>(quadTransform().matrix().getDouble(0, 3)),
-      static_cast<float>(quadTransform().matrix().getDouble(1, 3)));
-
-  // Transform the rect by the scale and offset.
-  gfx::RectF rect_f = rect;
-  rect_f.Scale(x_scale, y_scale);
-  rect_f += offset;
-
-  // Perform clipping and check to see if the result is empty.
-  gfx::RectF clipped_rect = IntersectRects(rect_f, clipRect());
-  if (clipped_rect.IsEmpty()) {
-    rect = gfx::Rect();
-    uv_top_left = gfx::PointF();
-    uv_bottom_right = gfx::PointF();
-    return true;
-  }
-
-  // Create a new uv-rect by clipping the old one to the new bounds.
-  gfx::Vector2dF uv_scale(uv_bottom_right - uv_top_left);
-  uv_scale.Scale(1.f / rect_f.width(), 1.f / rect_f.height());
-  uv_bottom_right = uv_top_left +
-      gfx::ScaleVector2d(
-          clipped_rect.bottom_right() - rect_f.origin(),
-          uv_scale.x(),
-          uv_scale.y());
-  uv_top_left = uv_top_left +
-      gfx::ScaleVector2d(
-          clipped_rect.origin() - rect_f.origin(),
-          uv_scale.x(),
-          uv_scale.y());
-
-  // Indexing according to the quad vertex generation:
-  // 1--2
-  // |  |
-  // 0--3
-  if (vertex_opacity[0] != vertex_opacity[1]
-      || vertex_opacity[0] != vertex_opacity[2]
-      || vertex_opacity[0] != vertex_opacity[3]) {
-    const float x1 = (clipped_rect.x() - rect_f.x()) / rect_f.width();
-    const float y1 = (clipped_rect.y() - rect_f.y()) / rect_f.height();
-    const float x3 = (clipped_rect.right() - rect_f.x()) / rect_f.width();
-    const float y3 = (clipped_rect.bottom() - rect_f.y()) / rect_f.height();
-    const float x1y1 = x1 * vertex_opacity[2] + (1.0f - x1) * vertex_opacity[1];
-    const float x1y3 = x1 * vertex_opacity[3] + (1.0f - x1) * vertex_opacity[0];
-    const float x3y1 = x3 * vertex_opacity[2] + (1.0f - x3) * vertex_opacity[1];
-    const float x3y3 = x3 * vertex_opacity[3] + (1.0f - x3) * vertex_opacity[0];
-    vertex_opacity[0] = y3 * x1y3 + (1.0f - y3) * x1y1;
-    vertex_opacity[1] = y1 * x1y3 + (1.0f - y1) * x1y1;
-    vertex_opacity[2] = y1 * x3y3 + (1.0f - y1) * x3y1;
-    vertex_opacity[3] = y3 * x3y3 + (1.0f - y3) * x3y1;
-  }
-
-  // Move the clipped rectangle back into its space.
-  clipped_rect -= offset;
-  clipped_rect.Scale(1.0f / x_scale, 1.0f / y_scale);
-  rect = gfx::Rect(static_cast<int>(clipped_rect.x() + 0.5f),
-                   static_cast<int>(clipped_rect.y() + 0.5f),
-                   static_cast<int>(clipped_rect.width() + 0.5f),
-                   static_cast<int>(clipped_rect.height() + 0.5f));
-  return true;
-}
-
 void TextureDrawQuad::ExtendValue(base::DictionaryValue* value) const {
   value->SetInteger("resource_id", resource_id);
   value->SetBoolean("premultiplied_alpha", premultiplied_alpha);