Add GrProcOptInfo class to track various output information for color and coverage stages.

src/gpu/GrProcOptInfo.cpp

Index: src/gpu/GrProcOptInfo.cpp
diff --git a/src/gpu/GrProcOptInfo.cpp b/src/gpu/GrProcOptInfo.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..c3ca100b61cbe7d1771945787b05573871de0d00
--- /dev/null
+++ b/src/gpu/GrProcOptInfo.cpp
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "GrProcOptInfo.h"
+
+#include "GrGeometryProcessor.h"
+#include "GrProcessorStage.h"
+
+void GrProcOptInfo::calcWithInitialValues(const GrFragmentStage* stages,
+                                          int stageCount,
+                                          GrColor startColor,
+                                          GrColorComponentFlags flags,
+                                          bool areCoverageStages,
+                                          const GrGeometryProcessor* gp) {
+    fInOut.reset(startColor, flags, areCoverageStages);
+    fFirstEffectStageIndex = 0;
+    fInputColorIsUsed = true;
+    fInputColor = startColor;
+    fRemoveVertexAttrib = false;
+    fReadsDst = false;
+
+    if (areCoverageStages && gp) {
+        gp->computeInvariantOutput(&fInOut);
+    }
+
+    for (int i = 0; i < stageCount; ++i) {
+        const GrFragmentProcessor* processor = stages[i].getProcessor();
+        fInOut.resetWillUseInputColor();
+        processor->computeInvariantOutput(&fInOut);
+        #ifdef SK_DEBUG
+        fInOut.validate();
+        #endif
+        if (!fInOut.willUseInputColor()) {
+            fFirstEffectStageIndex = i;
+            fInputColorIsUsed = false;
+            fReadsDst = false; // Reset this since we don't care if previous stages read dst

[bsalomon, 2014/11/13 15:09:19]

nice catch :)

+        }
+        if (processor->willReadDstColor()) {
+            fReadsDst = true;
+        }
+        if (kRGBA_GrColorComponentFlags == fInOut.validFlags()) {
+            fFirstEffectStageIndex = i + 1;
+            fInputColor = fInOut.color();
+            fInputColorIsUsed = true;
+            fRemoveVertexAttrib = true;
+            // Since we are clearing all previous color stages we are in a state where we have found
+            // zero stages that don't multiply the inputColor.
+            fInOut.resetNonMulStageFound();
+            fReadsDst = false; // Reset this since we don't care if previous stages read dst
+        }
+    }
+}