Compute minimal intermediate surface sizes in Advanced Layers. (bug 1375785, r=mattwoodrow)

gfx/layers/mlgpu/ContainerLayerMLGPU.cpp

@@ -8,11 +8,16 @@
 #include "LayersLogging.h"
 #include "LayerManagerMLGPU.h"
 #include "MLGDevice.h"
+#include "mozilla/gfx/Rect.h"
 #include "mozilla/gfx/Types.h"
+#include "UnitTransforms.h"
+#include "UtilityMLGPU.h"
 
 namespace mozilla {
 namespace layers {
 
+using namespace gfx;
+
 ContainerLayerMLGPU::ContainerLayerMLGPU(LayerManagerMLGPU* aManager)
   : ContainerLayer(aManager, nullptr)
   , LayerMLGPU(aManager)
@@ -33,6 +38,24 @@ ContainerLayerMLGPU::OnPrepareToRender(FrameBuilder* aBuilder)
     return true;
   }
 
+  if ((!mRenderTarget || mChildrenChanged) &&
+      gfxPrefs::AdvancedLayersEnableContainerResizing())
+  {
+    // Try to compute a more accurate visible region.
+    AL_LOG("Computing new surface size for container %p:\n", GetLayer());
+
+    Maybe<IntRect> bounds = ComputeIntermediateSurfaceBounds();
+    if (bounds) {
+      LayerIntRegion region = Move(GetShadowVisibleRegion());
+      region.AndWith(LayerIntRect::FromUnknownRect(bounds.value()));
+      AL_LOG("  computed bounds: %s\n", Stringify(bounds.value()).c_str());
+      AL_LOG("  new visible: %s\n", Stringify(region).c_str());
+
+      SetShadowVisibleRegion(Move(region));
+    }
+  }
+  mChildrenChanged = false;
+
   mTargetOffset = GetIntermediateSurfaceRect().TopLeft().ToUnknownPoint();
   mTargetSize = GetIntermediateSurfaceRect().Size().ToUnknownSize();
 
@@ -51,6 +74,89 @@ ContainerLayerMLGPU::OnPrepareToRender(FrameBuilder* aBuilder)
   return true;
 }
 
+static IntRect
+GetTransformedBounds(Layer* aLayer)
+{
+  IntRect bounds = aLayer->GetLocalVisibleRegion().GetBounds().ToUnknownRect();
+  if (bounds.IsEmpty()) {
+    return bounds;
+  }
+
+  const Matrix4x4& transform = aLayer->GetEffectiveTransform();
+  Rect rect = transform.TransformAndClipBounds(Rect(bounds), Rect::MaxIntRect());
+  rect.RoundOut();
+  rect.ToIntRect(&bounds);
+  return bounds;
+}
+
+static Maybe<IntRect>
+FindVisibleBounds(Layer* aLayer, const Maybe<RenderTargetIntRect>& aClip)
+{
+  AL_LOG("  visiting child %p\n", aLayer);
+  AL_LOG_IF(aClip, "  parent clip: %s\n", Stringify(aClip.value()).c_str());
+
+  ContainerLayer* container = aLayer->AsContainerLayer();
+  if (container && !container->UseIntermediateSurface()) {
+    Maybe<IntRect> accumulated = Some(IntRect());
+
+    // Traverse children.
+    for (Layer* child = container->GetFirstChild(); child; child = child->GetNextSibling()) {
+      Maybe<RenderTargetIntRect> clip = aClip;
+      if (const Maybe<ParentLayerIntRect>& childClip = child->AsHostLayer()->GetShadowClipRect()) {
+        RenderTargetIntRect rtChildClip =
+          TransformBy(ViewAs<ParentLayerToRenderTargetMatrix4x4>(
+                        aLayer->GetEffectiveTransform(),
+                        PixelCastJustification::RenderTargetIsParentLayerForRoot),
+                      childClip.value());
+        clip = IntersectMaybeRects(clip, Some(rtChildClip));
+        AL_LOG("    target clip: %s\n", Stringify(rtChildClip).c_str());
+        AL_LOG_IF(clip, "    full clip: %s\n", Stringify(clip.value()).c_str());
+      }
+
+      Maybe<IntRect> childBounds = FindVisibleBounds(child, clip);
+      if (!childBounds) {
+        return Nothing();
+      }
+
+      accumulated = accumulated->SafeUnion(childBounds.value());
+      if (!accumulated) {
+        return Nothing();
+      }
+    }
+    return accumulated;
+  }
+
+  IntRect bounds = GetTransformedBounds(aLayer);
+  AL_LOG("    layer bounds: %s\n", Stringify(bounds).c_str());
+
+  if (aClip) {
+    bounds = bounds.Intersect(aClip.value().ToUnknownRect());
+    AL_LOG("    clipped bounds: %s\n", Stringify(bounds).c_str());
+  }
+  return Some(bounds);
+}
+
+Maybe<IntRect>
+ContainerLayerMLGPU::ComputeIntermediateSurfaceBounds()
+{
+  Maybe<IntRect> bounds = Some(IntRect());
+  for (Layer* child = GetFirstChild(); child; child = child->GetNextSibling()) {
+    Maybe<RenderTargetIntRect> clip =
+       ViewAs<RenderTargetPixel>(child->AsHostLayer()->GetShadowClipRect(),
+                                 PixelCastJustification::RenderTargetIsParentLayerForRoot);
+    Maybe<IntRect> childBounds = FindVisibleBounds(child, clip);
+    if (!childBounds) {
+      return Nothing();
+    }
+
+    bounds = bounds->SafeUnion(childBounds.value());
+    if (!bounds) {
+      return Nothing();
+    }
+  }
+  return bounds;
+}
+
 void
 ContainerLayerMLGPU::OnLayerManagerChange(LayerManagerMLGPU* aManager)
 {