Distance field fixes for Android

- Expand glyph size by 2 on each side to compensate for bilerp lookup
- Correct for Adreno tendency to drop entire tile if any pixel has divide-by-0
- Fix blurriness on Adreno by using uv coords to compute gradient instead
  of st coords
- Add faster version for uniform scale

BUG=skia:2173
R=bsalomon@google.com

Author: jvanverth@google.com

Review URL: https://codereview.chromium.org/205343008

git-svn-id: http://skia.googlecode.com/svn/trunk@13955 2bbb7eff-a529-9590-31e7-b0007b416f81

2 files changed, 55 insertions, 26 deletions

diff --git a/src/gpu/effects/GrDistanceFieldTextureEffect.cpp b/src/gpu/effects/GrDistanceFieldTextureEffect.cpp
index 9159a701e3..cd80e06745 100755
--- a/src/gpu/effects/GrDistanceFieldTextureEffect.cpp
+++ b/src/gpu/effects/GrDistanceFieldTextureEffect.cpp
@@ -35,6 +35,8 @@ public:
         SkASSERT(1 == drawEffect.castEffect<GrDistanceFieldTextureEffect>().numVertexAttribs());
 
         SkAssertResult(builder->enableFeature(GrGLShaderBuilder::kStandardDerivatives_GLSLFeature));
+        const GrDistanceFieldTextureEffect& dfTexEffect =
+                                              drawEffect.castEffect<GrDistanceFieldTextureEffect>();
 
         SkString fsCoordName;
         const char* vsCoordName;
@@ -61,16 +63,37 @@ public:
         // we adjust for the effect of the transformation on the distance by using
         // the length of the gradient of the texture coordinates. We use st coordinates
         // to ensure we're mapping 1:1 from texel space to pixel space.
-        builder->fsCodeAppendf("\tvec2 st = %s*%s;\n", fsCoordName.c_str(), textureSizeUniName);
-        builder->fsCodeAppend("\tvec2 Jdx = dFdx(st);\n");
-        builder->fsCodeAppend("\tvec2 Jdy = dFdy(st);\n");
-        builder->fsCodeAppend("\tvec2 st_grad = normalize(st);\n");
-        builder->fsCodeAppend("\tvec2 grad = vec2(st_grad.x*Jdx.x + st_grad.y*Jdy.x,\n");
-        builder->fsCodeAppend("\t                 st_grad.x*Jdx.y + st_grad.y*Jdy.y);\n");
-
-        // this gives us a smooth step across approximately one fragment
-        // (assuming a radius of the diagonal of the fragment, hence a factor of sqrt(2)/2)
-        builder->fsCodeAppend("\tfloat afwidth = 0.7071*length(grad);\n");
+        builder->fsCodeAppendf("\tvec2 uv = %s;\n", fsCoordName.c_str());
+        builder->fsCodeAppendf("\tvec2 st = uv*%s;\n", textureSizeUniName);
+        builder->fsCodeAppend("\tfloat afwidth;\n");
+        if (dfTexEffect.isUniformScale()) {
+            // this gives us a smooth step across approximately one fragment
+            // (assuming a radius of the diagonal of the fragment, hence a factor of sqrt(2)/2)
+            builder->fsCodeAppend("\tafwidth = 0.7071*dFdx(st.x);\n");
+        } else {
+            builder->fsCodeAppend("\tvec2 Jdx = dFdx(st);\n");
+            builder->fsCodeAppend("\tvec2 Jdy = dFdy(st);\n");
+
+            builder->fsCodeAppend("\tvec2 uv_grad;\n");
+            if (builder->ctxInfo().caps()->dropsTileOnZeroDivide()) {
+                // this is to compensate for the Adreno, which likes to drop tiles on division by 0
+                builder->fsCodeAppend("\tfloat uv_len2 = dot(uv, uv);\n");
+                builder->fsCodeAppend("\tif (uv_len2 < 0.0001) {\n");
+                builder->fsCodeAppend("\t\tuv_grad = vec2(0.7071, 0.7071);\n");
+                builder->fsCodeAppend("\t} else {\n");
+                builder->fsCodeAppend("\t\tuv_grad = uv*inversesqrt(uv_len2);\n");
+                builder->fsCodeAppend("\t}\n");
+            } else {
+                builder->fsCodeAppend("\tuv_grad = normalize(uv);\n");
+            }
+            builder->fsCodeAppend("\tvec2 grad = vec2(uv_grad.x*Jdx.x + uv_grad.y*Jdy.x,\n");
+            builder->fsCodeAppend("\t                 uv_grad.x*Jdx.y + uv_grad.y*Jdy.y);\n");
+
+            // this gives us a smooth step across approximately one fragment
+            // (assuming a radius of the diagonal of the fragment, hence a factor of sqrt(2)/2)
+            builder->fsCodeAppend("\tafwidth = 0.7071*length(grad);\n");
+        }
+
         builder->fsCodeAppend("\tfloat val = smoothstep(-afwidth, afwidth, distance);\n");
 
         builder->fsCodeAppendf("\t%s = %s;\n", outputColor,
@@ -80,17 +103,24 @@ public:
     virtual void setData(const GrGLUniformManager& uman,
                          const GrDrawEffect& drawEffect) SK_OVERRIDE {
         SkASSERT(fTextureSizeUni.isValid());
-        const GrDistanceFieldTextureEffect& distanceFieldEffect =
-                                              drawEffect.castEffect<GrDistanceFieldTextureEffect>();
-        if (distanceFieldEffect.getSize().width() != fTextureSize.width() ||
-            distanceFieldEffect.getSize().height() != fTextureSize.height()) {
-            fTextureSize = distanceFieldEffect.getSize();
+
+        GrTexture* texture = drawEffect.effect()->get()->texture(0);
+        if (texture->width() != fTextureSize.width() ||
+            texture->height() != fTextureSize.height()) {
+            fTextureSize = SkSize::Make(texture->width(), texture->height());
             uman.set2f(fTextureSizeUni,
-                       distanceFieldEffect.getSize().width(),
-                       distanceFieldEffect.getSize().height());
+                       fTextureSize.width(),
+                       fTextureSize.height());
         }
     }
 
+    static inline EffectKey GenKey(const GrDrawEffect& drawEffect, const GrGLCaps&) {
+        const GrDistanceFieldTextureEffect& dfTexEffect =
+                                              drawEffect.castEffect<GrDistanceFieldTextureEffect>();
+
+        return dfTexEffect.isUniformScale() ? 0x1 : 0x0;
+    }
+
 private:
     GrGLUniformManager::UniformHandle fTextureSizeUni;
     SkSize                            fTextureSize;
@@ -102,9 +132,9 @@ private:
 
 GrDistanceFieldTextureEffect::GrDistanceFieldTextureEffect(GrTexture* texture,
                                                            const GrTextureParams& params,
-                                                           const SkISize& size)
+                                                           bool uniformScale)
     : fTextureAccess(texture, params)
-    , fSize(SkSize::Make(SkIntToScalar(size.width()), SkIntToScalar(size.height()))) {
+    , fUniformScale(uniformScale) {
     this->addTextureAccess(&fTextureAccess);
     this->addVertexAttrib(kVec2f_GrSLType);
 }
@@ -149,7 +179,6 @@ GrEffectRef* GrDistanceFieldTextureEffect::TestCreate(SkRandom* random,
     };
     GrTextureParams params(tileModes, random->nextBool() ? GrTextureParams::kBilerp_FilterMode :
                                                            GrTextureParams::kNone_FilterMode);
-    SkISize size = SkISize::Make(1024, 2048);
 
-    return GrDistanceFieldTextureEffect::Create(textures[texIdx], params, size);
+    return GrDistanceFieldTextureEffect::Create(textures[texIdx], params, random->nextBool());
 }
diff --git a/src/gpu/effects/GrDistanceFieldTextureEffect.h b/src/gpu/effects/GrDistanceFieldTextureEffect.h
index 1292c03221..212532e0a8 100644
--- a/src/gpu/effects/GrDistanceFieldTextureEffect.h
+++ b/src/gpu/effects/GrDistanceFieldTextureEffect.h
@@ -21,8 +21,8 @@ class GrGLDistanceFieldTextureEffect;
  */
 class GrDistanceFieldTextureEffect : public GrVertexEffect {
 public:
-    static GrEffectRef* Create(GrTexture* tex, const GrTextureParams& p, const SkISize& s) {
-        AutoEffectUnref effect(SkNEW_ARGS(GrDistanceFieldTextureEffect, (tex, p, s)));
+    static GrEffectRef* Create(GrTexture* tex, const GrTextureParams& para, bool uniformScale) {
+        AutoEffectUnref effect(SkNEW_ARGS(GrDistanceFieldTextureEffect, (tex, para, uniformScale)));
         return CreateEffectRef(effect);
     }
 
@@ -31,7 +31,7 @@ public:
     static const char* Name() { return "DistanceFieldTexture"; }
 
     virtual void getConstantColorComponents(GrColor* color, uint32_t* validFlags) const SK_OVERRIDE;
-    const SkSize& getSize() const { return fSize; }
+    bool isUniformScale() const { return fUniformScale; }
 
     typedef GrGLDistanceFieldTextureEffect GLEffect;
 
@@ -39,12 +39,12 @@ public:
 
 private:
     GrDistanceFieldTextureEffect(GrTexture* texture, const GrTextureParams& params,
-                                 const SkISize& textureSize);
+                                 bool uniformScale);
 
     virtual bool onIsEqual(const GrEffect& other) const SK_OVERRIDE;
 
     GrTextureAccess fTextureAccess;
-    SkSize          fSize;
+    bool            fUniformScale;
 
     GR_DECLARE_EFFECT_TEST;