Bug 764860 - Simplify and comment the clipPath code. r=longsonr.

layout/svg/base/src/nsSVGClipPathFrame.cpp

@@ -47,14 +47,35 @@ nsSVGClipPathFrame::ClipPaint(nsRenderingContext* aContext,
     mClipParentMatrix = new gfxMatrix(aMatrix);
   }
 
-  bool isTrivial = IsTrivial();
-
-  SVGAutoRenderState mode(aContext,
-                          isTrivial ? SVGAutoRenderState::CLIP
-                                    : SVGAutoRenderState::CLIP_MASK);
-
   gfxContext *gfx = aContext->ThebesContext();
 
+  nsISVGChildFrame *singleClipPathChild = nsnull;
+
+  if (IsTrivial(&singleClipPathChild)) {
+    // Notify our child that it's painting as part of a clipPath, and that
+    // we only require it to draw its path (it should skip filling, etc.):
+    SVGAutoRenderState mode(aContext, SVGAutoRenderState::CLIP);
+
+    if (!singleClipPathChild) {
+      // We have no children - the spec says clip away everything:
+      gfx->Rectangle(gfxRect());
+    } else {
+      singleClipPathChild->NotifySVGChanged(
+                             nsISVGChildFrame::DO_NOT_NOTIFY_RENDERING_OBSERVERS | 
+                             nsISVGChildFrame::TRANSFORM_CHANGED);
+      singleClipPathChild->PaintSVG(aContext, nsnull);
+    }
+    gfx->Clip();
+    gfx->NewPath();
+    return NS_OK;
+  }
+
+  // Seems like this is a non-trivial clipPath, so we need to use a clip mask.
+
+  // Notify our children that they're painting into a clip mask:
+  SVGAutoRenderState mode(aContext, SVGAutoRenderState::CLIP_MASK);
+
+  // Check if this clipPath is itself clipped by another clipPath:
   nsSVGClipPathFrame *clipPathFrame =
     nsSVGEffects::GetEffectProperties(this).GetClipPathFrame(nsnull);
   bool referencedClipIsTrivial;
@@ -134,11 +155,6 @@ nsSVGClipPathFrame::ClipPaint(nsRenderingContext* aContext,
     gfx->Restore();
   }
 
-  if (isTrivial) {
-    gfx->Clip();
-    gfx->NewPath();
-  }
-
   return NS_OK;
 }
 
@@ -185,13 +201,17 @@ nsSVGClipPathFrame::ClipHitTest(nsIFrame* aParent,
 }
 
 bool
-nsSVGClipPathFrame::IsTrivial()
+nsSVGClipPathFrame::IsTrivial(nsISVGChildFrame **aSingleChild)
 {
   // If the clip path is clipped then it's non-trivial
   if (nsSVGEffects::GetEffectProperties(this).GetClipPathFrame(nsnull))
     return false;
 
-  bool foundChild = false;
+  if (aSingleChild) {
+    *aSingleChild = nsnull;
+  }
+
+  nsISVGChildFrame *foundChild = nsnull;
 
   for (nsIFrame* kid = mFrames.FirstChild(); kid;
        kid = kid->GetNextSibling()) {
@@ -206,9 +226,12 @@ nsSVGClipPathFrame::IsTrivial()
       if (nsSVGEffects::GetEffectProperties(kid).GetClipPathFrame(nsnull))
         return false;
 
-      foundChild = true;
+      foundChild = svgChild;
     }
   }
+  if (aSingleChild) {
+    *aSingleChild = foundChild;
+  }
   return true;
 }
 

layout/svg/base/src/nsSVGClipPathFrame.h

@@ -11,6 +11,7 @@
 #include "nsSVGUtils.h"
 
 class nsRenderingContext;
+class nsISVGChildFrame;
 
 typedef nsSVGContainerFrame nsSVGClipPathFrameBase;
 
@@ -41,7 +42,7 @@ public:
   // Check if this clipPath is made up of more than one geometry object.
   // If so, the clipping API in cairo isn't enough and we need to use
   // mask based clipping.
-  bool IsTrivial();
+  bool IsTrivial(nsISVGChildFrame **aSingleChild = nsnull);
 
   bool IsValid();
 

layout/svg/base/src/nsSVGGlyphFrame.cpp

@@ -317,6 +317,9 @@ nsSVGGlyphFrame::PaintSVG(nsRenderingContext *aContext,
   }
 
   if (renderMode != SVGAutoRenderState::NORMAL) {
+    NS_ABORT_IF_FALSE(renderMode == SVGAutoRenderState::CLIP ||
+                      renderMode == SVGAutoRenderState::CLIP_MASK,
+                      "Unknown render mode");
     gfxContextMatrixAutoSaveRestore matrixAutoSaveRestore(gfx);
     SetupGlobalTransform(gfx);
 

layout/svg/base/src/nsSVGIntegrationUtils.cpp

@@ -252,8 +252,6 @@ nsSVGIntegrationUtils::PaintFramesWithEffects(nsRenderingContext* aCtx,
   gfxContext* gfx = aCtx->ThebesContext();
   gfxContextMatrixAutoSaveRestore matrixAutoSaveRestore(gfx);
 
-  //SVGAutoRenderState autoRenderState(aCtx, SVGAutoRenderState::NORMAL);
-
   nsRect userSpaceRect = GetNonSVGUserSpace(firstFrame) + aBuilder->ToReferenceFrame(firstFrame);
   PRInt32 appUnitsPerDevPixel = aEffectsFrame->PresContext()->AppUnitsPerDevPixel();
   userSpaceRect = userSpaceRect.ToNearestPixels(appUnitsPerDevPixel).ToAppUnits(appUnitsPerDevPixel);

layout/svg/base/src/nsSVGPathGeometryFrame.cpp

@@ -461,6 +461,9 @@ nsSVGPathGeometryFrame::Render(nsRenderingContext *aContext)
   GeneratePath(gfx);
 
   if (renderMode != SVGAutoRenderState::NORMAL) {
+    NS_ABORT_IF_FALSE(renderMode == SVGAutoRenderState::CLIP ||
+                      renderMode == SVGAutoRenderState::CLIP_MASK,
+                      "Unknown render mode");
     gfx->Restore();
 
     if (GetClipRule() == NS_STYLE_FILL_RULE_EVENODD)

layout/svg/base/src/nsSVGUtils.h

@@ -161,7 +161,25 @@ private:
 class NS_STACK_CLASS SVGAutoRenderState
 {
 public:
-  enum RenderMode { NORMAL, CLIP, CLIP_MASK };
+  enum RenderMode {
+    /**
+     * Used to inform SVG frames that they should paint as normal.
+     */
+    NORMAL, 
+    /** 
+     * Used to inform SVG frames when they are painting as the child of a
+     * simple clipPath. In this case they should only draw their basic geometry
+     * as a path. They should not fill, stroke, or paint anything else.
+     */
+    CLIP, 
+    /** 
+     * Used to inform SVG frames when they are painting as the child of a
+     * complex clipPath that requires the use of a clip mask. In this case they
+     * should only draw their basic geometry as a path and then fill it using
+     * fully opaque white. They should not stroke, or paint anything else.
+     */
+    CLIP_MASK 
+  };
 
   SVGAutoRenderState(nsRenderingContext *aContext, RenderMode aMode);
   ~SVGAutoRenderState();