Disable gpu-side clip mask merging in the clip mask manager

src/gpu/GrClipMaskManager.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrClipMaskManager.h"
 #include "GrCaps.h"
 #include "GrDrawContext.h"
@@ skipping 36 matching lines @@
 }
 
 // Does the path in 'element' require SW rendering? If so, return true (and,
 // optionally, set 'prOut' to NULL. If not, return false (and, optionally, set
 // 'prOut' to the non-SW path renderer that will do the job).
 static bool path_needs_SW_renderer(GrContext* context,
                                    const GrPipelineBuilder& pipelineBuilder,
                                    const SkMatrix& viewMatrix,
                                    const Element* element,
                                    GrPathRenderer** prOut,
-                                   bool tryStencilFirst) {
+                                   bool needsStencil) {
     if (Element::kRect_Type == element->getType()) {
         // rects can always be drawn directly w/o using the software path
         // TODO: skip rrects once we're drawing them directly.
         if (prOut) {
             *prOut = nullptr;
         }
         return false;
     } else {
         // We shouldn't get here with an empty clip element.
         SkASSERT(Element::kEmpty_Type != element->getType());
 
         // the gpu alpha mask will draw the inverse paths as non-inverse to a temp buffer
         SkPath path;
         element->asPath(&path);
         if (path.isInverseFillType()) {
             path.toggleInverseFillType();
         }
         GrStrokeInfo stroke(SkStrokeRec::kFill_InitStyle);
     
         GrPathRendererChain::DrawType type;
         
-        if (tryStencilFirst) {
+        if (needsStencil) {
             type = element->isAA()
                             ? GrPathRendererChain::kStencilAndColorAntiAlias_DrawType
                             : GrPathRendererChain::kStencilAndColor_DrawType;
         } else {
             type = element->isAA()
                             ? GrPathRendererChain::kColorAntiAlias_DrawType
                             : GrPathRendererChain::kColor_DrawType;    
         }
     
         // the 'false' parameter disallows use of the SW path renderer
         GrPathRenderer* pr = context->getPathRenderer(pipelineBuilder, viewMatrix, path,
                                                       stroke, false, type);
-        if (tryStencilFirst && !pr) {
-            // If the path can't be stenciled, createAlphaClipMask falls back to color rendering
-            // it into a temporary buffer. If that fails then SW is truly required.
-            type = element->isAA()
-                            ? GrPathRendererChain::kColorAntiAlias_DrawType
-                            : GrPathRendererChain::kColor_DrawType;  
-
-            pr = context->getPathRenderer(pipelineBuilder, viewMatrix, path, stroke, false, type);
-        }
-
         if (prOut) {
             *prOut = pr;
         }
         return SkToBool(!pr);
     }
 }
 
+// Determines whether it is possible to draw the element to both the stencil buffer and the
+// alpha mask simultaneously. If so and the element is a path a compatible path renderer is
+// also returned.
+static bool can_stencil_and_draw_element(GrContext* context,
+                                         GrPipelineBuilder* pipelineBuilder,
+                                         GrTexture* texture,
+                                         const SkMatrix& viewMatrix,
+                                         const SkClipStack::Element* element,
+                                         GrPathRenderer** pr) {
+    pipelineBuilder->setRenderTarget(texture->asRenderTarget());
+
+    static const bool kNeedsStencil = true;
+    return !path_needs_SW_renderer(context,
+                                   *pipelineBuilder,
+                                   viewMatrix,
+                                   element,
+                                   pr,
+                                   kNeedsStencil);
+}
+
 GrClipMaskManager::GrClipMaskManager(GrDrawTarget* drawTarget)
     : fDrawTarget(drawTarget)
     , fClipMode(kIgnoreClip_StencilClipMode) {
 }
 
 GrContext* GrClipMaskManager::getContext() { return fDrawTarget->cmmAccess().context(); }
 
 /*
  * This method traverses the clip stack to see if the GrSoftwarePathRenderer
  * will be used on any element. If so, it returns true to indicate that the
  * entire clip should be rendered in SW and then uploaded en masse to the gpu.
  */
 bool GrClipMaskManager::useSWOnlyPath(const GrPipelineBuilder& pipelineBuilder,
                                       const SkVector& clipToMaskOffset,
                                       const GrReducedClip::ElementList& elements) {
     // TODO: generalize this function so that when
     // a clip gets complex enough it can just be done in SW regardless
     // of whether it would invoke the GrSoftwarePathRenderer.
 
     // Set the matrix so that rendered clip elements are transformed to mask space from clip
     // space.
     const SkMatrix translate = SkMatrix::MakeTrans(clipToMaskOffset.fX, clipToMaskOffset.fY);
 
     for (GrReducedClip::ElementList::Iter iter(elements.headIter()); iter.get(); iter.next()) {
         const Element* element = iter.get();
 
         SkRegion::Op op = element->getOp();
         bool invert = element->isInverseFilled();
-        bool tryStencilFirst = invert || 
-                               SkRegion::kIntersect_Op == op ||
-                               SkRegion::kReverseDifference_Op == op;
+        bool needsStencil = invert || 
+                            SkRegion::kIntersect_Op == op || SkRegion::kReverseDifference_Op == op;
 
         if (path_needs_SW_renderer(this->getContext(), pipelineBuilder, translate,
-                                   element, nullptr, tryStencilFirst)) {
+                                   element, nullptr, needsStencil)) {
             return true;
         }
     }
     return false;
 }
 
 bool GrClipMaskManager::getAnalyticClipProcessor(const GrReducedClip::ElementList& elements,
                                                  bool abortIfAA,
                                                  SkVector& clipToRTOffset,
                                                  const SkRect* drawBounds,
@@ skipping 314 matching lines @@
             args.fPath = &path;
             args.fStroke = &stroke;
             args.fAntiAlias = element->isAA();
             pr->drawPath(args);
             break;
         }
     }
     return true;
 }
 
-bool GrClipMaskManager::canStencilAndDrawElement(GrPipelineBuilder* pipelineBuilder,
-                                                 GrTexture* target,
-                                                 GrPathRenderer** pr,
-                                                 const SkClipStack::Element* element) {
-    pipelineBuilder->setRenderTarget(target->asRenderTarget());
-
-    if (Element::kRect_Type == element->getType()) {
-        return true;
-    } else {
-        // We shouldn't get here with an empty clip element.
-        SkASSERT(Element::kEmpty_Type != element->getType());
-        SkPath path;
-        element->asPath(&path);
-        if (path.isInverseFillType()) {
-            path.toggleInverseFillType();
-        }
-        GrStrokeInfo stroke(SkStrokeRec::kFill_InitStyle);
-        GrPathRendererChain::DrawType type = element->isAA() ?
-            GrPathRendererChain::kStencilAndColorAntiAlias_DrawType :
-            GrPathRendererChain::kStencilAndColor_DrawType;
-        *pr = this->getContext()->getPathRenderer(*pipelineBuilder, SkMatrix::I(), path,
-                                                  stroke, false, type);
-        return SkToBool(*pr);
-    }
-}
-
 void GrClipMaskManager::mergeMask(GrPipelineBuilder* pipelineBuilder,
                                   GrTexture* dstMask,
                                   GrTexture* srcMask,
                                   SkRegion::Op op,
                                   const SkIRect& dstBound,
                                   const SkIRect& srcBound) {
     pipelineBuilder->setRenderTarget(dstMask->asRenderTarget());
 
     // We want to invert the coverage here
     set_coverage_drawing_xpf(op, false, pipelineBuilder);
@@ skipping 105 matching lines @@
     // walk through each clip element and perform its set op
     for (GrReducedClip::ElementList::Iter iter = elements.headIter(); iter.get(); iter.next()) {
         const Element* element = iter.get();
         SkRegion::Op op = element->getOp();
         bool invert = element->isInverseFilled();
         if (invert || SkRegion::kIntersect_Op == op || SkRegion::kReverseDifference_Op == op) {
             GrPipelineBuilder pipelineBuilder;
 
             pipelineBuilder.setClip(clip);
             GrPathRenderer* pr = nullptr;
-            bool useTemp = !this->canStencilAndDrawElement(&pipelineBuilder, texture, &pr, element);
+            bool useTemp = !can_stencil_and_draw_element(this->getContext(), &pipelineBuilder,
+                                                         texture, translate, element, &pr);
+
+            // useSWOnlyPath should now filter out all cases where gpu-side mask merging is
+            // performed. See skbug.com/4519 for rationale and details.
+            SkASSERT(!useTemp);
+
             GrTexture* dst;
             // This is the bounds of the clip element in the space of the alpha-mask. The temporary
             // mask buffer can be substantially larger than the actually clip stack element. We
             // touch the minimum number of pixels necessary and use decal mode to combine it with
             // the accumulator.
             SkIRect maskSpaceElementIBounds;
 
             if (useTemp) {
                 if (invert) {
                     maskSpaceElementIBounds = maskSpaceIBounds;
@@ skipping 515 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 
 void GrClipMaskManager::adjustPathStencilParams(const GrStencilAttachment* stencilAttachment,
                                                 GrStencilSettings* settings) {
     if (stencilAttachment) {
         int stencilBits = stencilAttachment->bits();
         this->adjustStencilParams(settings, fClipMode, stencilBits);
     }
 }