Bug 1370564 - Add suppport for blur filter. r=kats

MozReview-Commit-ID: EYoYbbIs3wH

--HG--
extra : rebase_source : afb1030fbd3592fa5a373d0657d345ec45d70d11

layout/painting/nsDisplayList.cpp

@@ -9581,6 +9581,13 @@ nsDisplayFilter::PaintAsLayer(nsDisplayListBuilder* aBuilder,
   nsDisplayFilterGeometry::UpdateDrawResult(this, imgParams.result);
 }
 
+static float
+ClampStdDeviation(float aStdDeviation)
+{
+  // Cap software blur radius for performance reasons.
+  return std::min(std::max(0.0f, aStdDeviation), 100.0f);
+}
+
 bool
 nsDisplayFilter::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuilder,
                                          mozilla::wr::IpcResourceUpdateQueue& aResources,
@@ -9611,6 +9618,18 @@ nsDisplayFilter::CreateWebRenderCommands(mozilla::wr::DisplayListBuilder& aBuild
         wrFilters.AppendElement(filterOp);
         break;
       }
+      case NS_STYLE_FILTER_BLUR: {
+        float appUnitsPerDevPixel = mFrame->PresContext()->AppUnitsPerDevPixel();
+        mozilla::wr::WrFilterOp filterOp = {
+          wr::ToWrFilterOpType(filter.GetType()),
+          ClampStdDeviation(
+            NSAppUnitsToFloatPixels(
+              filter.GetFilterParameter().GetCoordValue(),
+              appUnitsPerDevPixel)),
+        };
+        wrFilters.AppendElement(filterOp);
+        break;
+      }
       default:
         return false;
     }