Program key coverage/discard fixes.

src/gpu/gl/GrGLProgram.cpp

Index: src/gpu/gl/GrGLProgram.cpp
===================================================================
--- src/gpu/gl/GrGLProgram.cpp	(revision 8392)
+++ src/gpu/gl/GrGLProgram.cpp	(working copy)
@@ -117,13 +117,6 @@
 
     int lastEnabledStage = -1;
 
-    if (!skipCoverage) {
-        desc->fDiscardIfOutsideEdge = drawState.getStencil().doesWrite();
-    } else {
-        // Use canonical values when edge-aa is not enabled to avoid program cache misses.
-        desc->fDiscardIfOutsideEdge = false;
-    }
-
     for (int s = 0; s < GrDrawState::kNumStages; ++s) {
 
         bool skip = s < drawState.getFirstCoverageStage() ? skipColor : skipCoverage;
@@ -152,26 +145,36 @@
 #endif
 #endif
 
-    // We want to avoid generating programs with different "first cov stage" values when they would
-    // compute the same result. We set field in the desc to kNumStages when either there are no
-    // coverage stages or the distinction between coverage and color is immaterial.
+    // We leave this set to kNumStages until we discover that the coverage/color distinction is
+    // material to the generated program. We do this to avoid distinct keys that generate equivalent
+    // programs.
+    desc->fFirstCoverageStage = GrDrawState::kNumStages;
+    // This tracks the actual first coverage stage.
     int firstCoverageStage = GrDrawState::kNumStages;
-    desc->fFirstCoverageStage = GrDrawState::kNumStages;
-    bool hasCoverage = drawState.getFirstCoverageStage() <= lastEnabledStage;
-    if (hasCoverage) {
-        firstCoverageStage = drawState.getFirstCoverageStage();
+    desc->fDiscardIfZeroCoverage = false; // Enabled below if stenciling and there is coverage.
+    bool hasCoverage = false;
+    // If we're rendering coverage-as-color then its as though there are no coverage stages.
+    if (!drawState.isCoverageDrawing()) {
+        // We can have coverage either through a stage or coverage vertex attributes.
+        if (drawState.getFirstCoverageStage() <= lastEnabledStage) {
+            firstCoverageStage = drawState.getFirstCoverageStage();
+            hasCoverage = true;
+        } else {
+            hasCoverage = requiresAttributeCoverage;
+        }
     }
-
-    // other coverage inputs
-    if (!hasCoverage) {
-        hasCoverage = requiresAttributeCoverage;
-    }
-
+    
     if (hasCoverage) {
         // color filter is applied between color/coverage computation
         if (SkXfermode::kDst_Mode != desc->fColorFilterXfermode) {
             desc->fFirstCoverageStage = firstCoverageStage;
         }
+        
+        // If we're stenciling then we want to discard samples that have zero coverage
+        if (drawState.getStencil().doesWrite()) {
+            desc->fDiscardIfZeroCoverage = true;
+            desc->fFirstCoverageStage = firstCoverageStage;
+        }
 
         if (gpu->caps()->dualSourceBlendingSupport() &&
             !(blendOpts & (GrDrawState::kEmitCoverage_BlendOptFlag |
@@ -797,7 +800,7 @@
             }
 
             // discard if coverage is zero
-            if (fDesc.fDiscardIfOutsideEdge && !outCoverage.isEmpty()) {
+            if (fDesc.fDiscardIfZeroCoverage && !outCoverage.isEmpty()) {
                 builder.fsCodeAppendf(
                     "\tif (all(lessThanEqual(%s, vec4(0.0)))) {\n\t\tdiscard;\n\t}\n",
                     outCoverage.c_str());