Analytic rrect clip for cicular corners, radius >= .5

src/gpu/effects/GrRRectEffect.cpp

+/*
+ * 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 "GrRRectEffect.h"
+
+#include "gl/GrGLEffect.h"
+#include "gl/GrGLSL.h"
+#include "GrTBackendEffectFactory.h"
+
+#include "SkPath.h"
+
+// This effect only supports circular corner rrects where all corners have the same radius
+// which must be <= kRadiusMin.
+static const SkScalar kRadiusMin = 0.5;
+
+//////////////////////////////////////////////////////////////////////////////
+class GrGLRRectEffect : public GrGLEffect {
+public:
+    GrGLRRectEffect(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&) { return 0; }
+
+    virtual void setData(const GrGLUniformManager&, const GrDrawEffect&) SK_OVERRIDE;
+
+private:
+    GrGLUniformManager::UniformHandle   fInnerRectUniform;
+    GrGLUniformManager::UniformHandle   fRadiusPlusHalfUniform;
+    SkRRect                             fPrevRRect;
+    typedef GrGLEffect INHERITED;
+};
+
+GrGLRRectEffect::GrGLRRectEffect(const GrBackendEffectFactory& factory,
+                                 const GrDrawEffect& drawEffect)
+    : INHERITED (factory) {
+    fPrevRRect.setEmpty();
+}
+
+void GrGLRRectEffect::emitCode(GrGLShaderBuilder* builder,
+                               const GrDrawEffect& drawEffect,
+                               EffectKey key,
+                               const char* outputColor,
+                               const char* inputColor,
+                               const TransformedCoordsArray&,
+                               const TextureSamplerArray& samplers) {
+    const char *rectName;
+    const char *radiusPlusHalfName;
+    // The inner rect is the rrect bounds inset by the radius. Its top, left, right, and bottom
+    // edges correspond to components x, y, z, and w, respectively.
+    fInnerRectUniform = builder->addUniform(GrGLShaderBuilder::kFragment_Visibility,
+                                            kVec4f_GrSLType,
+                                            "innerRect",
+                                            &rectName);
+    fRadiusPlusHalfUniform = builder->addUniform(GrGLShaderBuilder::kFragment_Visibility,
+                                                 kFloat_GrSLType,
+                                                 "radiusPlusHalf",
+                                                 &radiusPlusHalfName);
+    const char* fragmentPos = builder->fragmentPosition();
+    // At each quarter-circle corner we compute a vector that is the offset of the fragment position
+    // from the circle center. The vector is pinned in x and y to be in the quarter-plane relevant
+    // to that corner. This means that points near the interior near the rrect top edge will have
+    // a vector that points straight up for both the TL left and TR corners. Computing an
+    // alpha from this vector at either the TR or TL corner will give the correct result. Similarly,
+    // fragments near the other three edges will get the correct AA. Fragments in the interior of
+    // the rrect will have a (0,0) vector at all four corners. So long as the radius > 0.5 they will
+    // correctly produce an alpha value of 1 at all four corners. We take the min of all the alphas.
+    // The code below is a simplified version of the above that performs maxs on the vector
+    // components before computing distances and alpha values so that only one distance computation
+    // need be computed to determine the min alpha.
+    builder->fsCodeAppendf("\t\tvec2 dxy0 = %s.xy - %s.xy;\n", rectName, fragmentPos);
+    builder->fsCodeAppendf("\t\tvec2 dxy1 = %s.xy - %s.zw;\n", fragmentPos, rectName);
+    builder->fsCodeAppend("\t\tvec2 dxy = max(max(dxy0, dxy1), 0.0);\n");
+    builder->fsCodeAppendf("\t\tfloat alpha = clamp(%s - length(dxy), 0.0, 1.0);\n",
+                           radiusPlusHalfName);
+
+    builder->fsCodeAppendf("\t\t%s = %s;\n", outputColor,
+                           (GrGLSLExpr4(inputColor) * GrGLSLExpr1("alpha")).c_str());
+}
+
+void GrGLRRectEffect::setData(const GrGLUniformManager& uman, const GrDrawEffect& drawEffect) {
+    const GrRRectEffect& rre = drawEffect.castEffect<GrRRectEffect>();
+    const SkRRect& rrect = rre.getRRect();
+    if (rrect != fPrevRRect) {
+        SkASSERT(rrect.isSimpleCircular());
+        SkRect rect = rrect.getBounds();
+        SkScalar radius = rrect.getSimpleRadii().fX;
+        SkASSERT(radius >= kRadiusMin);
+        rect.inset(radius, radius);
+        uman.set4f(fInnerRectUniform, rect.fLeft, rect.fTop, rect.fRight, rect.fBottom);
+        uman.set1f(fRadiusPlusHalfUniform, radius + 0.5f);
+        fPrevRRect = rrect;
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+GrEffectRef* GrRRectEffect::Create(const SkRRect& rrect) {
+    if (!rrect.isSimpleCircular()) {
+        return NULL;
+    }
+    if (rrect.getSimpleRadii().fX < kRadiusMin) {
+        return NULL;
+    }
+    return CreateEffectRef(AutoEffectUnref(SkNEW_ARGS(GrRRectEffect, (rrect))));
+}
+
+GrRRectEffect::~GrRRectEffect() {}
+
+void GrRRectEffect::getConstantColorComponents(GrColor* color, uint32_t* validFlags) const {
+    *validFlags = 0;
+}
+
+const GrBackendEffectFactory& GrRRectEffect::getFactory() const {
+    return GrTBackendEffectFactory<GrRRectEffect>::getInstance();
+}
+
+GrRRectEffect::GrRRectEffect(const SkRRect& rrect)
+    : fRRect(rrect) {
+    SkASSERT(rrect.isSimpleCircular());
+    SkASSERT(rrect.getSimpleRadii().fX >= kRadiusMin);
+    this->setWillReadFragmentPosition();
+}
+
+bool GrRRectEffect::onIsEqual(const GrEffect& other) const {
+    const GrRRectEffect& rre = CastEffect<GrRRectEffect>(other);
+    return fRRect == rre.fRRect;
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+GR_DEFINE_EFFECT_TEST(GrRRectEffect);
+
+GrEffectRef* GrRRectEffect::TestCreate(SkRandom* random,
+                                       GrContext*,
+                                       const GrDrawTargetCaps& caps,
+                                       GrTexture*[]) {
+    SkScalar w = random->nextRangeScalar(20.f, 1000.f);
+    SkScalar h = random->nextRangeScalar(20.f, 1000.f);
+    SkScalar r = random->nextRangeF(kRadiusMin, 9.f);
+    SkRRect rrect;
+    rrect.setRectXY(SkRect::MakeWH(w, h), r, r);
+
+    return GrRRectEffect::Create(rrect);
+}