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, 9 insertions, 0 deletions

diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index a60230a2fe..47f3f0f0c8 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -47,6 +47,7 @@ void GrGLCaps::reset() {
     fFixedFunctionSupport = false;
     fDiscardFBSupport = false;
     fFullClearIsFree = false;
+    fDropsTileOnZeroDivide = false;
 }
 
 GrGLCaps::GrGLCaps(const GrGLCaps& caps) : GrDrawTargetCaps() {
@@ -84,6 +85,7 @@ GrGLCaps& GrGLCaps::operator = (const GrGLCaps& caps) {
     fFixedFunctionSupport = caps.fFixedFunctionSupport;
     fDiscardFBSupport = caps.fDiscardFBSupport;
     fFullClearIsFree = caps.fFullClearIsFree;
+    fDropsTileOnZeroDivide = caps.fDropsTileOnZeroDivide;
 
     return *this;
 }
@@ -244,6 +246,9 @@ void GrGLCaps::init(const GrGLContextInfo& ctxInfo, const GrGLInterface* gli) {
         }
     }
 
+    // Adreno GPUs have a tendency to drop tiles when there is a divide-by-zero in a shader
+    fDropsTileOnZeroDivide = kQualcomm_GrGLVendor == ctxInfo.vendor();
+
     this->initFSAASupport(ctxInfo, gli);
     this->initStencilFormats(ctxInfo);
 
@@ -661,5 +666,6 @@ SkString GrGLCaps::dump() const {
              (fUseNonVBOVertexAndIndexDynamicData ? "YES" : "NO"));
     r.appendf("Discard FrameBuffer support: %s\n", (fDiscardFBSupport ? "YES" : "NO"));
     r.appendf("Full screen clear is free: %s\n", (fFullClearIsFree ? "YES" : "NO"));
+    r.appendf("Drops tile on zero divide: %s\n", (fDropsTileOnZeroDivide ? "YES" : "NO"));
     return r;
 }
diff --git a/src/gpu/gl/GrGLCaps.h b/src/gpu/gl/GrGLCaps.h
index 7f0c8874ca..0939f80c26 100644
--- a/src/gpu/gl/GrGLCaps.h
+++ b/src/gpu/gl/GrGLCaps.h
@@ -250,6 +250,8 @@ public:
 
     bool fullClearIsFree() const { return fFullClearIsFree; }
 
+    bool dropsTileOnZeroDivide() const { return fDropsTileOnZeroDivide; }
+
 private:
     /**
      * Maintains a bit per GrPixelConfig. It is used to avoid redundantly
@@ -332,6 +334,7 @@ private:
     bool fFixedFunctionSupport : 1;
     bool fDiscardFBSupport : 1;
     bool fFullClearIsFree : 1;
+    bool fDropsTileOnZeroDivide : 1;
 
     typedef GrDrawTargetCaps INHERITED;
 };