Add convex polygon rendering effect and GM to test it.

src/gpu/effects/GrConvexPolyEffect.cpp

Index: src/gpu/effects/GrConvexPolyEffect.cpp
diff --git a/src/gpu/effects/GrConvexPolyEffect.cpp b/src/gpu/effects/GrConvexPolyEffect.cpp
new file mode 100644
index 0000000000000000000000000000000000000000..189b26d49c610b6dd5000bad992dd0e43db20845
--- /dev/null
+++ b/src/gpu/effects/GrConvexPolyEffect.cpp
@@ -0,0 +1,184 @@
+/*
+ * 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 "GrConvexPolyEffect.h"
+
+#include "gl/GrGLEffect.h"
+#include "gl/GrGLSL.h"
+#include "gl/GrGLVertexEffect.h"
+#include "GrTBackendEffectFactory.h"
+
+#include "SkPath.h"
+
+class GrGLConvexPolyEffect : public GrGLEffect {
+public:
+    GrGLConvexPolyEffect(const GrBackendEffectFactory&, const GrDrawEffect&);
+
+    virtual void emitCode(GrGLShaderBuilder* builder,
+                          const GrDrawEffect& drawEffect,
+                          EffectKey key,
+                          const char* outputColor,
+                          const char* inputColor,
+                          const TransformedCoordsArray&,
+                          const TextureSamplerArray&) SK_OVERRIDE;
+
+    static inline EffectKey GenKey(const GrDrawEffect&, const GrGLCaps&);
+
+    virtual void setData(const GrGLUniformManager&, const GrDrawEffect&) SK_OVERRIDE;
+
+private:
+    GrGLUniformManager::UniformHandle   fEdgeUniform;
+    SkScalar                            fPrevEdges[3 * GrConvexPolyEffect::kMaxEdges];
+    typedef GrGLEffect INHERITED;
+};
+
+GrGLConvexPolyEffect::GrGLConvexPolyEffect(const GrBackendEffectFactory& factory,
+                                           const GrDrawEffect& drawEffect)
+    : INHERITED (factory) {
+    fPrevEdges[0] = SK_ScalarNaN;
+}
+
+void GrGLConvexPolyEffect::emitCode(GrGLShaderBuilder* builder,
+                                    const GrDrawEffect& drawEffect,
+                                    EffectKey key,
+                                    const char* outputColor,
+                                    const char* inputColor,
+                                    const TransformedCoordsArray&,
+                                    const TextureSamplerArray& samplers) {
+    const GrConvexPolyEffect& cpe = drawEffect.castEffect<GrConvexPolyEffect>();
+
+    const char *edgeArrayName;
+    fEdgeUniform = builder->addUniformArray(GrGLShaderBuilder::kFragment_Visibility,
+                                            kVec3f_GrSLType,
+                                            "edges",
+                                            cpe.getEdgeCount(),
+                                            &edgeArrayName);
+    builder->fsCodeAppend("\t\tfloat alpha = 1.0;\n");
+    builder->fsCodeAppend("\t\tfloat edge;\n");
+    const char* fragmentPos = builder->fragmentPosition();
+    for (int i = 0; i < cpe.getEdgeCount(); ++i) {
+        builder->fsCodeAppendf("\t\tedge = dot(%s[%d], vec3(%s.x, %s.y, 1));\n",
+                               edgeArrayName, i, fragmentPos, fragmentPos);
+        switch (cpe.getEdgeType()) {
+            case GrConvexPolyEffect::kFillAA_EdgeType:
+                builder->fsCodeAppend("\t\tedge = clamp(edge, 0.0, 1.0);\n");
+                builder->fsCodeAppend("\t\talpha *= edge;\n");
+                break;
+            case GrConvexPolyEffect::kFillNoAA_EdgeType:
+                builder->fsCodeAppend("\t\tedge = edge >= 0.5 ? 1.0 : 0.0;\n");
+                builder->fsCodeAppend("\t\talpha *= edge;\n");
+                break;
+        }
+    }
+
+    builder->fsCodeAppendf("\t%s = %s;\n", outputColor,
+                           (GrGLSLExpr4(inputColor) * GrGLSLExpr1("alpha")).c_str());
+}
+
+void GrGLConvexPolyEffect::setData(const GrGLUniformManager& uman, const GrDrawEffect& drawEffect) {
+    const GrConvexPolyEffect& cpe = drawEffect.castEffect<GrConvexPolyEffect>();
+    size_t byteSize = 3 * cpe.getEdgeCount() * sizeof(SkScalar);
+    if (0 != memcmp(fPrevEdges, cpe.getEdges(), byteSize)) {
+        uman.set3fv(fEdgeUniform, cpe.getEdgeCount(), cpe.getEdges());
+        memcpy(fPrevEdges, cpe.getEdges(), byteSize);
+    }
+}
+
+GrGLEffect::EffectKey GrGLConvexPolyEffect::GenKey(const GrDrawEffect& drawEffect,
+                                                   const GrGLCaps&) {
+    const GrConvexPolyEffect& cpe = drawEffect.castEffect<GrConvexPolyEffect>();
+    GR_STATIC_ASSERT(GrConvexPolyEffect::kEdgeTypeCnt <= 4);
+    return (cpe.getEdgeCount() << 2) | cpe.getEdgeType();
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+GrEffectRef* GrConvexPolyEffect::Create(EdgeType type, const SkPath& path) {
+    if (path.getSegmentMasks() != SkPath::kLine_SegmentMask ||
+        !path.isConvex() ||
+        path.isInverseFillType()) {
+        return NULL;
+    }
+
+    if (path.countPoints() > kMaxEdges) {
+        return NULL;
+    }
+
+    SkPoint pts[kMaxEdges];
+    SkScalar edges[3 * kMaxEdges];
+
+    SkPath::Direction dir;
+    SkAssertResult(path.cheapComputeDirection(&dir));
+
+    int count = path.getPoints(pts, kMaxEdges);
+    int n = 0;
+    for (int lastPt = count - 1, i = 0; i < count; lastPt = i++) {
+        if (pts[lastPt] != pts[i]) {
+            SkVector v = pts[i] - pts[lastPt];
+            v.normalize();
+            if (SkPath::kCCW_Direction == dir) {
+                edges[3 * n] = v.fY;
+                edges[3 * n + 1] = -v.fX;
+            } else {
+                edges[3 * n] = -v.fY;
+                edges[3 * n + 1] = v.fX;
+            }
+            edges[3 * n + 2] = -(edges[3 * n] * pts[i].fX + edges[3 * n + 1] * pts[i].fY);
+            ++n;
+        }
+    }
+    return Create(type, n, edges);
+}
+
+GrConvexPolyEffect::~GrConvexPolyEffect() {}
+
+void GrConvexPolyEffect::getConstantColorComponents(GrColor* color, uint32_t* validFlags) const {
+    *validFlags = 0;
+}
+
+const GrBackendEffectFactory& GrConvexPolyEffect::getFactory() const {
+    return GrTBackendEffectFactory<GrConvexPolyEffect>::getInstance();
+}
+
+GrConvexPolyEffect::GrConvexPolyEffect(EdgeType edgeType, int n, const SkScalar edges[])
+    : fEdgeType(edgeType)
+    , fEdgeCount(n) {
+    SkASSERT(n <= kMaxEdges);

[robertphillips, 2014/01/29 20:57:55]

Should we just clamp n at kMaxEdges? We could document that if you pass us too
many we're just going to truncate the list.

[bsalomon, 2014/01/29 22:19:42]

The Create() function is responsible for handling this. Currently it returns
NULL. This assert is just here to ensure that all the Create() variants are
doing their job. It really should never fire even if a public caller gave a
large n. Comment added.

+    memcpy(fEdges, edges, 3 * n * sizeof(SkScalar));
+    // Outset the edges by 0.5 so that a pixel with center on an edge is 50% covered in the AA case
+    // and 100% covered in the non-AA case.
+    for (int i = 0; i < n; ++i) {
+        fEdges[3 * i + 2] += SK_ScalarHalf;
+    }
+    this->setWillReadFragmentPosition();
+}
+
+bool GrConvexPolyEffect::onIsEqual(const GrEffect& other) const {
+    const GrConvexPolyEffect& cpe = CastEffect<GrConvexPolyEffect>(other);
+    // ignore the fact that 0 == -0 and just use memcmp.
+    return (cpe.fEdgeType == fEdgeType && cpe.fEdgeCount == fEdgeCount &&
+            0 == memcmp(cpe.fEdges, fEdges, 3 * fEdgeCount * sizeof(SkScalar)));
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+GR_DEFINE_EFFECT_TEST(GrConvexPolyEffect);
+
+GrEffectRef* GrConvexPolyEffect::TestCreate(SkRandom* random,
+                                            GrContext*,
+                                            const GrDrawTargetCaps& caps,
+                                            GrTexture*[]) {
+    EdgeType edgeType = static_cast<EdgeType>(random->nextULessThan(kEdgeTypeCnt));
+    int count = random->nextULessThan(kMaxEdges + 1);
+    SkScalar edges[kMaxEdges * 3];
+    for (int i = 0; i < 3 * count; ++i) {
+        edges[i] = random->nextSScalar1();

[robertphillips, 2014/01/29 20:57:55]

Don't we need to normalize here?

[bsalomon, 2014/01/29 22:19:42]

Done.

+    }
+
+    return GrConvexPolyEffect::Create(edgeType, count, edges);
+}
+