1 files changed, 60 insertions, 0 deletions
diff --git a/gfx/layers/LayersHelpers.cpp b/gfx/layers/LayersHelpers.cpp
new file mode 100644
index 0000000000..72f194aa48
--- /dev/null
+++ b/gfx/layers/LayersHelpers.cpp
@@ -0,0 +1,60 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#include "LayersHelpers.h"
+
+namespace mozilla {
+namespace layers {
+
+using namespace gfx;
+
+gfx::IntRect ComputeBackdropCopyRect(const gfx::Rect& aRect,
+                                     const gfx::IntRect& aClipRect,
+                                     const gfx::Matrix4x4& aTransform,
+                                     const gfx::IntRect& aRenderTargetRect,
+                                     gfx::Matrix4x4* aOutTransform,
+                                     gfx::Rect* aOutLayerQuad) {
+  // Compute the clip.
+  IntPoint rtOffset = aRenderTargetRect.TopLeft();
+  IntSize rtSize = aRenderTargetRect.Size();
+
+  gfx::IntRect renderBounds(0, 0, rtSize.width, rtSize.height);
+  renderBounds.IntersectRect(renderBounds, aClipRect);
+  renderBounds.MoveBy(rtOffset);
+
+  // Apply the layer transform.
+  RectDouble dest = aTransform.TransformAndClipBounds(
+      RectDouble(aRect.X(), aRect.Y(), aRect.Width(), aRect.Height()),
+      RectDouble(renderBounds.X(), renderBounds.Y(), renderBounds.Width(),
+                 renderBounds.Height()));
+  dest -= rtOffset;
+
+  // Ensure we don't round out to -1, which trips up Direct3D.
+  dest.IntersectRect(dest, RectDouble(0, 0, rtSize.width, rtSize.height));
+
+  if (aOutLayerQuad) {
+    *aOutLayerQuad = Rect(dest.X(), dest.Y(), dest.Width(), dest.Height());
+  }
+
+  // Round out to integer.
+  IntRect result;
+  dest.RoundOut();
+  dest.ToIntRect(&result);
+
+  // Create a transform from adjusted clip space to render target space,
+  // translate it for the backdrop rect, then transform it into the backdrop's
+  // uv-space.
+  Matrix4x4 transform;
+  transform.PostScale(rtSize.width, rtSize.height, 1.0);
+  transform.PostTranslate(-result.X(), -result.Y(), 0.0);
+  transform.PostScale(1 / float(result.Width()), 1 / float(result.Height()),
+                      1.0);
+  *aOutTransform = transform;
+  return result;
+}
+
+}  // namespace layers
+}  // namespace mozilla