Bug 716403 - Annotate layers with the fixed margins from the PresShell. r=nrc,roc

This annotates fixed layers with the margins that have been applied from
nsIPresShell->GetContentDocumentFixedPositionMargins. Using SyncViewportInfo
in CompositorParent, this allows for async fixed position margin setting.

gfx/2d/Rect.h

@@ -18,6 +18,7 @@ struct Margin :
   typedef BaseMargin<Float, Margin> Super;
 
   // Constructors
+  Margin() : Super(0, 0, 0, 0) {}
   Margin(const Margin& aMargin) : Super(aMargin) {}
   Margin(Float aTop, Float aRight, Float aBottom, Float aLeft)
     : Super(aTop, aRight, aBottom, aLeft) {}

gfx/layers/Layers.cpp

@@ -320,6 +320,7 @@ Layer::Layer(LayerManager* aManager, void* aImplData) :
   mUseClipRect(false),
   mUseTileSourceRect(false),
   mIsFixedPosition(false),
+  mMargins(0, 0, 0, 0),
   mDebugColorIndex(0),
   mAnimationGeneration(0)
 {}

gfx/layers/Layers.h

@@ -844,6 +844,16 @@ public:
    */
   void SetFixedPositionAnchor(const gfxPoint& aAnchor) { mAnchor = aAnchor; }
 
+  /**
+   * CONSTRUCTION PHASE ONLY
+   * If a layer represents a fixed position element or elements that are on
+   * a document that has had fixed position element margins set on it, these
+   * will be mirrored here. This allows for asynchronous animation of the
+   * margins by reconciling the difference between this value and a value that
+   * is updated more frequently.
+   */
+  void SetFixedPositionMargins(const gfx::Margin& aMargins) { mMargins = aMargins; }
+
   // These getters can be used anytime.
   float GetOpacity() { return mOpacity; }
   const nsIntRect* GetClipRect() { return mUseClipRect ? &mClipRect : nullptr; }
@@ -860,6 +870,7 @@ public:
   float GetPostYScale() { return mPostYScale; }
   bool GetIsFixedPosition() { return mIsFixedPosition; }
   gfxPoint GetFixedPositionAnchor() { return mAnchor; }
+  const gfx::Margin& GetFixedPositionMargins() { return mMargins; }
   Layer* GetMaskLayer() { return mMaskLayer; }
 
   // Note that all lengths in animation data are either in CSS pixels or app
@@ -1208,6 +1219,7 @@ protected:
   bool mUseTileSourceRect;
   bool mIsFixedPosition;
   gfxPoint mAnchor;
+  gfx::Margin mMargins;
   DebugOnly<uint32_t> mDebugColorIndex;
   // If this layer is used for OMTA, then this counter is used to ensure we
   // stay in sync with the animation manager

gfx/layers/ipc/CompositorParent.cpp

@@ -652,17 +652,23 @@ CompositorParent::TransformFixedLayers(Layer* aLayer,
     gfxPoint translation(aTranslation - (anchor - anchor / aScaleDiff));
 
     // Offset this translation by the fixed layer margins, depending on what
-    // side of the viewport the layer is anchored to.
+    // side of the viewport the layer is anchored to, reconciling the
+    // difference between the current fixed layer margins and the Gecko-side
+    // fixed layer margins.
+    // aFixedLayerMargins are the margins we expect to be at at the current
+    // time, obtained via SyncViewportInfo, and fixedMargins are the margins
+    // that were used during layout.
+    const gfx::Margin& fixedMargins = aLayer->GetFixedPositionMargins();
     if (anchor.x > 0) {
-      translation.x -= aFixedLayerMargins.right;
+      translation.x -= aFixedLayerMargins.right - fixedMargins.right;
     } else {
-      translation.x += aFixedLayerMargins.left;
+      translation.x += aFixedLayerMargins.left - fixedMargins.left;
     }
 
     if (anchor.y > 0) {
-      translation.y -= aFixedLayerMargins.bottom;
+      translation.y -= aFixedLayerMargins.bottom - fixedMargins.bottom;
     } else {
-      translation.y += aFixedLayerMargins.top;
+      translation.y += aFixedLayerMargins.top - fixedMargins.top;
     }
 
     // The transform already takes the resolution scale into account.  Since we

gfx/layers/ipc/PLayers.ipdl

@@ -26,6 +26,7 @@ using mozilla::TimeStamp;
 using mozilla::ScreenRotation;
 using nsCSSProperty;
 using mozilla::dom::ScreenOrientation;
+using mozilla::gfx::Margin;
 
 /**
  * The layers protocol is spoken between thread contexts that manage
@@ -185,6 +186,7 @@ struct CommonLayerAttributes {
   nsIntRect clipRect;
   bool isFixedPosition;
   gfxPoint fixedPositionAnchor;
+  Margin fixedPositionMargin;
   nullable PLayer maskLayer;
   // Animated colors will only honored for ColorLayers.
   Animation[] animations;

gfx/layers/ipc/ShadowLayers.cpp

@@ -344,6 +344,7 @@ ShadowLayerForwarder::EndTransaction(InfallibleTArray<EditReply>* aReplies)
                          *mutant->GetClipRect() : nsIntRect());
     common.isFixedPosition() = mutant->GetIsFixedPosition();
     common.fixedPositionAnchor() = mutant->GetFixedPositionAnchor();
+    common.fixedPositionMargin() = mutant->GetFixedPositionMargins();
     if (Layer* maskLayer = mutant->GetMaskLayer()) {
       common.maskLayerChild() = Shadow(maskLayer->AsShadowableLayer());
     } else {

gfx/layers/ipc/ShadowLayersParent.cpp

@@ -248,6 +248,7 @@ ShadowLayersParent::RecvUpdate(const InfallibleTArray<Edit>& cset,
       layer->SetPostScale(common.postXScale(), common.postYScale());
       layer->SetIsFixedPosition(common.isFixedPosition());
       layer->SetFixedPositionAnchor(common.fixedPositionAnchor());
+      layer->SetFixedPositionMargins(common.fixedPositionMargin());
       if (PLayerParent* maskLayer = common.maskLayerParent()) {
         layer->SetMaskLayer(cast(maskLayer)->AsLayer());
       } else {

ipc/glue/IPCMessageUtils.h

@@ -836,6 +836,28 @@ struct ParamTraits<mozilla::gfx::Rect>
   }
 };
 
+template<>
+struct ParamTraits<mozilla::gfx::Margin>
+{
+  typedef mozilla::gfx::Margin paramType;
+
+  static void Write(Message* msg, const paramType& param)
+  {
+    WriteParam(msg, param.top);
+    WriteParam(msg, param.right);
+    WriteParam(msg, param.bottom);
+    WriteParam(msg, param.left);
+  }
+
+  static bool Read(const Message* msg, void** iter, paramType* result)
+  {
+    return (ReadParam(msg, iter, &result->top) &&
+            ReadParam(msg, iter, &result->right) &&
+            ReadParam(msg, iter, &result->bottom) &&
+            ReadParam(msg, iter, &result->left));
+  }
+};
+
 template<>
 struct ParamTraits<nsRect>
 {

layout/base/nsDisplayList.cpp

@@ -2978,6 +2978,19 @@ nsDisplayFixedPosition::BuildLayer(nsDisplayListBuilder* aBuilder,
 
   layer->SetFixedPositionAnchor(anchor);
 
+  // Also make sure the layer is aware of any fixed position margins that have
+  // been set.
+  nsMargin fixedMargins = presContext->PresShell()->GetContentDocumentFixedPositionMargins();
+  mozilla::gfx::Margin fixedLayerMargins(NSAppUnitsToFloatPixels(fixedMargins.top, factor) *
+                                           aContainerParameters.mYScale,
+                                         NSAppUnitsToFloatPixels(fixedMargins.right, factor) *
+                                           aContainerParameters.mXScale,
+                                         NSAppUnitsToFloatPixels(fixedMargins.bottom, factor) *
+                                           aContainerParameters.mYScale,
+                                         NSAppUnitsToFloatPixels(fixedMargins.left, factor) *
+                                           aContainerParameters.mXScale);
+  layer->SetFixedPositionMargins(fixedLayerMargins);
+
   return layer.forget();
 }