From ccec906120d39df409e728130e7f7f4dfa0ab760 Mon Sep 17 00:00:00 2001
From: Matt Woodrow <mwoodrow@mozilla.com>
Date: Thu, 2 May 2019 22:02:30 +0000
Subject: [PATCH] Bug 1547159 - Composite just the visible rects of
 ColorLayerComposite on mobile. r=jnicol

Differential Revision: https://phabricator.services.mozilla.com/D29456

--HG--
extra : moz-landing-system : lando
---
 gfx/layers/composite/ColorLayerComposite.cpp | 31 ++++++++++++++------
 1 file changed, 22 insertions(+), 9 deletions(-)

diff --git a/gfx/layers/composite/ColorLayerComposite.cpp b/gfx/layers/composite/ColorLayerComposite.cpp
index b32438344985..1dea139bad13 100644
--- a/gfx/layers/composite/ColorLayerComposite.cpp
+++ b/gfx/layers/composite/ColorLayerComposite.cpp
@@ -22,19 +22,32 @@ using namespace mozilla::gfx;
 
 void ColorLayerComposite::RenderLayer(const gfx::IntRect& aClipRect,
                                       const Maybe<gfx::Polygon>& aGeometry) {
-  Rect rect(GetBounds());
-
   const Matrix4x4& transform = GetEffectiveTransform();
 
-  RenderWithAllMasks(this, mCompositor, aClipRect,
-                     [&](EffectChain& effectChain, const IntRect& clipRect) {
-                       GenEffectChain(effectChain);
+#ifdef MOZ_GFX_OPTIMIZE_MOBILE
+  // On desktop we want to draw a single rectangle to avoid possible
+  // seams if we're resampling. On mobile we'd prefer to use the accurate
+  // region for better performance.
+  LayerIntRegion drawRegion = GetLocalVisibleRegion();
+#else
+  LayerIntRegion drawRegion = ViewAs<LayerPixel>(GetBounds());
+#endif
 
-                       mCompositor->DrawGeometry(rect, clipRect, effectChain,
-                                                 GetEffectiveOpacity(),
-                                                 transform, aGeometry);
-                     });
+  for (auto iter = drawRegion.RectIter(); !iter.Done(); iter.Next()) {
+    const LayerIntRect& rect = iter.Get();
+    Rect graphicsRect(rect.X(), rect.Y(), rect.Width(), rect.Height());
 
+    RenderWithAllMasks(this, mCompositor, aClipRect,
+                       [&](EffectChain& effectChain, const IntRect& clipRect) {
+                         GenEffectChain(effectChain);
+
+                         mCompositor->DrawGeometry(
+                             graphicsRect, clipRect, effectChain,
+                             GetEffectiveOpacity(), transform, aGeometry);
+                       });
+  }
+
+  Rect rect(GetBounds());
   mCompositor->DrawDiagnostics(DiagnosticFlags::COLOR, rect, aClipRect,
                                transform);
 }