First pass at Rect Effect

src/gpu/effects/GrRectEffect.cpp

Index: src/gpu/effects/GrRectEffect.cpp
===================================================================
--- src/gpu/effects/GrRectEffect.cpp	(revision 0)
+++ src/gpu/effects/GrRectEffect.cpp	(revision 0)
@@ -0,0 +1,102 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "GrRectEffect.h"
+#include "gl/GrGLEffect.h"
+#include "gl/GrGLEffectMatrix.h"
+#include "gl/GrGLSL.h"
+#include "gl/GrGLTexture.h"
+#include "GrTBackendEffectFactory.h"
+#include "GrTexture.h"
+
+class GrGLRectEffect : public GrGLEffect {
+public:
+    GrGLRectEffect(const GrBackendEffectFactory& factory, const GrDrawEffect&)
+    : INHERITED (factory) {}
+
+    virtual void emitCode(GrGLShaderBuilder* builder,
+                          const GrDrawEffect& drawEffect,
+                          EffectKey key,
+                          const char* outputColor,
+                          const char* inputColor,
+                          const TextureSamplerArray& samplers) SK_OVERRIDE {
+        // setup the varying for the center point and the unit vector
+        // that points down the height of the rect
+        const char *vsRectEdgeName, *fsRectEdgeName;
+        builder->addVarying(kVec4f_GrSLType, "RectEdge", 
+                            &vsRectEdgeName, &fsRectEdgeName);
+        const SkString* attr0Name = 
+            builder->getEffectAttributeName(drawEffect.getVertexAttribIndices()[0]);
+        builder->vsCodeAppendf("\t%s = %s;\n", vsRectEdgeName, attr0Name->c_str());
+
+        // setup the varying for width/2+.5 and height/2+.5
+        const char *vsWidthHeightName, *fsWidthHeightName;
+        builder->addVarying(kVec2f_GrSLType, "WidthHeight", 
+                            &vsWidthHeightName, &fsWidthHeightName);
+        const SkString* attr1Name =
+            builder->getEffectAttributeName(drawEffect.getVertexAttribIndices()[1]);
+        builder->vsCodeAppendf("\t%s = %s;\n", vsWidthHeightName, attr1Name->c_str());
+
+        // These scale factors adjust the coverage for < 1 pixel wide/high rects
+        builder->fsCodeAppendf("\tfloat wScale = max(1.0, 2.0/(0.5+%s.x));\n", fsWidthHeightName);

[bsalomon, 2013/04/08 15:48:39]

Do you think it makes sense to do this in the VS?

[robertphillips, 2013/04/08 19:33:20]

Yes but I would like to delay to the next revision. I have added a reminder
TODO.

+        builder->fsCodeAppendf("\tfloat hScale = max(1.0, 2.0/(0.5+%s.y));\n", fsWidthHeightName);
+
+        // Compute the coverage for the rect's width
+        builder->fsCodeAppendf("\tvec2 offset = %s.xy - %s.xy;\n", 
+                               builder->fragmentPosition(), fsRectEdgeName);
+        builder->fsCodeAppendf("\tfloat perpDot = abs(offset.x * %s.w - offset.y * %s.z);\n",
+                               fsRectEdgeName, fsRectEdgeName);
+        builder->fsCodeAppendf("\tfloat coverage = clamp(wScale*(%s.x-perpDot), 0.0, 1.0);\n",
+                               fsWidthHeightName);
+
+        // Compute the coverage for the rect's height and merge with the width
+        builder->fsCodeAppendf("\tperpDot = abs(dot(offset, %s.zw));\n",
+                               fsRectEdgeName);
+        builder->fsCodeAppendf("\tcoverage = min(coverage, clamp(hScale*(%s.y-perpDot), 0.0, 1.0));\n",
+                               fsWidthHeightName);
+
+        SkString modulate;
+        GrGLSLModulate4f(&modulate, inputColor, "coverage");
+        builder->fsCodeAppendf("\t%s = %s;\n", outputColor, modulate.c_str());
+    }
+
+    static inline EffectKey GenKey(const GrDrawEffect& drawEffect, const GrGLCaps&) {
+        return 0;
+    }
+
+    virtual void setData(const GrGLUniformManager& uman, const GrDrawEffect&) SK_OVERRIDE {
+    }
+
+private:
+    typedef GrGLEffect INHERITED;
+};
+
+///////////////////////////////////////////////////////////////////////////////
+
+GrRectEffect::GrRectEffect() : GrEffect() {
+    this->addVertexAttrib(kVec4f_GrSLType);
+    this->addVertexAttrib(kVec2f_GrSLType);
+}
+
+void GrRectEffect::getConstantColorComponents(GrColor* color, uint32_t* validFlags) const {
+    *validFlags = 0;
+}
+
+const GrBackendEffectFactory& GrRectEffect::getFactory() const {
+    return GrTBackendEffectFactory<GrRectEffect>::getInstance();
+}
+
+///////////////////////////////////////////////////////////////////////////////
+
+GR_DEFINE_EFFECT_TEST(GrRectEffect);
+
+GrEffectRef* GrRectEffect::TestCreate(SkMWCRandom* random,
+                                      GrContext* context,
+                                      const GrDrawTargetCaps&,
+                                      GrTexture* textures[]) {
+    return GrRectEffect::Create();
+}