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

src/gpu/GrProcOptInfo.h

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrProcOptInfo_DEFINED
+#define GrProcOptInfo_DEFINED
+
+#include "GrColor.h"
+#include "GrInvariantOutput.h"
+
+class GrFragmentStage;
+class GrGeometryProcessor;
+
+/**
+ * GrProcOptInfo gathers invariant data from a set of processor stages.It is used to recognize
+ * optimizations related to eliminating stages and vertex attributes that aren't necessary for a
+ * draw.
+ */
+class GrProcOptInfo {
+public:
+    GrProcOptInfo()
+        : fInOut(0, static_cast<GrColorComponentFlags>(0), false)
+        , fFirstEffectStageIndex(0)
+        , fInputColorIsUsed(true)
+        , fInputColor(0)
+        , fRemoveVertexAttrib(false)
+        , fReadsDst(false) {}
+
+    void calcWithInitialValues(const GrFragmentStage*, int stageCount, GrColor startColor,
+                               GrColorComponentFlags flags, bool areCoverageStages,
+                               const GrGeometryProcessor* gp = NULL);
+
+    bool isSolidWhite() const { return fInOut.isSolidWhite(); }
+    bool isOpaque() const { return fInOut.isOpaque(); }
+
+    GrColor color() const { return fInOut.color(); }
+    uint8_t validFlags() const { return fInOut.validFlags(); }
+
+    /**
+     * Returns the index of the first effective color stage. If an intermediate stage doesn't read
+     * its input or has a known output, then we can ignore all earlier stages since they will not
+     * affect the final output. Thus the first effective stage index is the index to the first stage
+     * that will have an effect on the final output.
+     *
+     * If stages before the firstEffectiveStageIndex are removed, corresponding values from
+     * inputColorIsUsed(), inputColorToEffectiveStage(), removeVertexAttribs(), and readsDst() must
+     * be used when setting up the draw to ensure correct drawing.
+     */
+    int firstEffectiveStageIndex() const { return fFirstEffectStageIndex; }
+
+    /**
+     * True if the first effective stage reads its input, false otherwise.
+     */
+    bool inputColorIsUsed() const { return fInputColorIsUsed; }
+
+    /**
+     * If input color is used and per-vertex colors are not used, this is the input color to the
+     * first effective stage.
+     */
+    GrColor inputColorToEffectiveStage() const { return fInputColor; }
+
+    /**
+     * Given the set of optimizations determined by GrProcOptInfo, should the caller remove the
+     * color/coverage vertex attribute that was input to the first stage.
+     */
+    bool removeVertexAttrib() const { return fRemoveVertexAttrib; }
+
+    /**
+     * Returns true if any of the stages preserved by GrProcOptInfo read the dst color.
+     */
+    bool readsDst() const { return fReadsDst; }
+
+private:
+    GrInvariantOutput fInOut;
+    int fFirstEffectStageIndex;
+    bool fInputColorIsUsed;
+    GrColor fInputColor;
+    bool fRemoveVertexAttrib;
+    bool fReadsDst;
+};
+
+#endif