Bug 1535029 - Store the render root rect as a ScreenRect. r=dthayer

The main change here is removing some rounding so that we can do more
accurate hit-testing in APZ. Instead of rounding both the rect and the
point, we just store both as unrounded values. mRenderRootRects is also
changed to be of a Screen type as that better reflects what it's being
used for, and there is a legitimate justification for converting it from
LayoutDevice.

Depends on D25239

Differential Revision: https://phabricator.services.mozilla.com/D25240

--HG--
extra : moz-landing-system : lando

gfx/layers/apz/src/APZCTreeManager.cpp

@@ -3198,8 +3198,7 @@ already_AddRefed<wr::WebRenderAPI> APZCTreeManager::GetWebRenderAPIAtPoint(
   CompositorBridgeParent::CallWithIndirectShadowTree(
       mRootLayersId, [&](LayerTreeState& aState) -> void {
         if (aState.mWrBridge) {
-          IntPoint point = RoundedToInt(aPoint).ToUnknownPoint();
+          api = aState.mWrBridge->GetWebRenderAPIAtPoint(aPoint);
-          api = aState.mWrBridge->GetWebRenderAPIAtPoint(point);
         }
       });
   return api.forget();

gfx/layers/wr/WebRenderBridgeParent.cpp

@@ -914,7 +914,8 @@ bool WebRenderBridgeParent::SetDisplayList(
     if (IsRootWebRenderBridgeParent()) {
       if (aRenderRoot != wr::RenderRoot::Default) {
         MutexAutoLock lock(mRenderRootRectMutex);
-        mRenderRootRects[aRenderRoot] = RoundedToInt(aRect).ToUnknownRect();
+        mRenderRootRects[aRenderRoot] = ViewAs<ScreenPixel>(
+            aRect, PixelCastJustification::LayoutDeviceIsScreenForTabDims);
       }
       LayoutDeviceIntSize widgetSize = mWidget->GetClientSize();
       LayoutDeviceIntRect rect = RoundedToInt(aRect);
@@ -2019,7 +2020,7 @@ void WebRenderBridgeParent::HoldPendingTransactionId(
 }
 
 already_AddRefed<wr::WebRenderAPI>
-WebRenderBridgeParent::GetWebRenderAPIAtPoint(const gfx::IntPoint& aPoint) {
+WebRenderBridgeParent::GetWebRenderAPIAtPoint(const ScreenPoint& aPoint) {
   MutexAutoLock lock(mRenderRootRectMutex);
   for (auto renderRoot : wr::kNonDefaultRenderRoots) {
     if (mRenderRootRects[renderRoot].Contains(aPoint)) {

gfx/layers/wr/WebRenderBridgeParent.h

@@ -80,7 +80,7 @@ class WebRenderBridgeParent final
     return true;
   }
   already_AddRefed<wr::WebRenderAPI> GetWebRenderAPIAtPoint(
-      const gfx::IntPoint& aPoint);
+      const ScreenPoint& aPoint);
   already_AddRefed<wr::WebRenderAPI> GetWebRenderAPI(
       wr::RenderRoot aRenderRoot) {
     if ((size_t)aRenderRoot >= mApis.Length()) {
@@ -468,7 +468,7 @@ class WebRenderBridgeParent final
   // Kind of clunky, but I can't sort out a more elegant way of getting this to
   // work.
   Mutex mRenderRootRectMutex;
-  wr::NonDefaultRenderRootArray<IntRect> mRenderRootRects;
+  wr::NonDefaultRenderRootArray<ScreenRect> mRenderRootRects;
 
   wr::RenderRoot mRenderRoot;
   bool mPaused;