[Not For Commit] Deferred building of PaintLayer filter-chain

third_party/WebKit/Source/core/paint/PaintLayer.cpp

Index: third_party/WebKit/Source/core/paint/PaintLayer.cpp
diff --git a/third_party/WebKit/Source/core/paint/PaintLayer.cpp b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
index ded24777fc93352efa5270495cbf6fd8340df234..c800588ef9d07d2dc95d0e24a2aa304851827115 100644
--- a/third_party/WebKit/Source/core/paint/PaintLayer.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayer.cpp
@@ -1061,7 +1061,7 @@ LayoutRect PaintLayer::transparencyClipBox(const PaintLayer* layer, const PaintL
         // paints unfragmented.
         LayoutRect clipRect = layer->physicalBoundingBox(layer);
         expandClipRectForDescendantsAndReflection(clipRect, layer, layer, transparencyBehavior, subPixelAccumulation, globalPaintFlags);
-        clipRect.expand(layer->layoutObject()->style()->filterOutsets());
+        clipRect.expand(layer->filterOutsets());
         LayoutRect result = transform.mapRect(clipRect);
         if (!paginationLayer)
             return result;
@@ -1080,7 +1080,7 @@ LayoutRect PaintLayer::transparencyClipBox(const PaintLayer* layer, const PaintL
 
     LayoutRect clipRect = layer->fragmentsBoundingBox(rootLayer);
     expandClipRectForDescendantsAndReflection(clipRect, layer, rootLayer, transparencyBehavior, subPixelAccumulation, globalPaintFlags);
-    clipRect.expand(layer->layoutObject()->style()->filterOutsets());
+    clipRect.expand(layer->filterOutsets());
     clipRect.move(subPixelAccumulation);
     return clipRect;
 }
@@ -2195,7 +2195,7 @@ LayoutRect PaintLayer::boundingBoxForCompositing(const PaintLayer* ancestorLayer
         // FIXME: We can optimize the size of the composited layers, by not enlarging
         // filtered areas with the outsets if we know that the filter is going to render in hardware.
         // https://bugs.webkit.org/show_bug.cgi?id=81239
-        result.expand(m_layoutObject->style()->filterOutsets());
+        result.expand(filterOutsets());
     }
 
     if (transform() && paintsWithTransform(GlobalPaintNormalPhase) && (this != ancestorLayer || options == MaybeIncludeTransformForAncestorLayer))
@@ -2573,7 +2573,7 @@ FilterOperations computeFilterOperationsHandleReferenceFilters(const FilterOpera
 
 } // unnamed namespace
 
-FilterOperations PaintLayer::computeFilterOperations(const ComputedStyle& style)
+FilterOperations PaintLayer::computeFilterOperations(const ComputedStyle& style) const
 {
     return computeFilterOperationsHandleReferenceFilters(style.filter(), style.effectiveZoom(), enclosingElement());
 }
@@ -2583,6 +2583,13 @@ FilterOperations PaintLayer::computeBackdropFilterOperations(const ComputedStyle
     return computeFilterOperationsHandleReferenceFilters(style.backdropFilter(), style.effectiveZoom(), enclosingElement());
 }
 
+FilterOutsets PaintLayer::filterOutsets() const
+{
+    // Ensure the filter-chain is refreshed wrt reference filters.
+    filterEffectBuilder();
+    return layoutObject()->style()->filterOutsets();
+}
+
 void PaintLayer::updateOrRemoveFilterClients()
 {
     if (!hasFilter()) {
@@ -2602,23 +2609,33 @@ void PaintLayer::updateOrRemoveFilterEffectBuilder()
     // so we always need to run updateOrRemoveFilterEffectBuilder after the composited
     // mode might have changed for this layer.
     if (!paintsWithFilters()) {
-        // Don't delete the whole filter info here, because we might use it
-        // for loading CSS shader files.
-        if (PaintLayerFilterInfo* filterInfo = this->filterInfo())
-            filterInfo->setBuilder(nullptr);
-
+        removeFilterInfoIfNeeded();

[Stephen White, 2015/11/19 17:50:41]

Could you explain the rationale for this change?

[fs, 2015/11/19 18:34:24]

Just based on the comment about "CSS shader files" (Custom Filters), which makes
it seem like a remnant that could be simplified.

         return;
     }
 
     PaintLayerFilterInfo* filterInfo = ensureFilterInfo();
+    if (filterInfo->builder())
+        filterInfo->builder()->reset();
+}
+
+FilterEffectBuilder* PaintLayer::filterEffectBuilder() const
+{
+    PaintLayerFilterInfo* filterInfo = this->filterInfo();
+    if (!filterInfo)
+        return nullptr;
+
     if (!filterInfo->builder())
         filterInfo->setBuilder(FilterEffectBuilder::create());
 
+    // TODO(fs): Could check builder()->lastEffect() here to avoid rebuilding the filter chain.

[Stephen White, 2015/11/19 17:50:41]

It does seem to be unpleasant to be doing this on every call to filterOutsets().

[fs, 2015/11/19 18:34:24]

Indeed.

+    const ComputedStyle& style = layoutObject()->styleRef();
     // If the filter fails to build, remove it from the layer. It will still attempt to
     // go through regular processing (e.g. compositing), but never apply anything.
-    float zoom = layoutObject()->style() ? layoutObject()->style()->effectiveZoom() : 1.0f;
-    if (!filterInfo->builder()->build(toElement(enclosingElement()), computeFilterOperations(layoutObject()->styleRef()), zoom))
+    float zoom = style.effectiveZoom();
+    if (!filterInfo->builder()->build(toElement(enclosingElement()), computeFilterOperations(style), zoom))
         filterInfo->setBuilder(nullptr);
+
+    return filterInfo->builder();
 }
 
 void PaintLayer::filterNeedsPaintInvalidation()