Infer sampler precision from pixel config

include/gpu/GrCaps.h

Index: include/gpu/GrCaps.h
diff --git a/include/gpu/GrCaps.h b/include/gpu/GrCaps.h
index d698a4142c2b5f783d1753e8678f18b96615b7de..d3faf26c60f02a63a6d37ea47ec0295943dff543 100644
--- a/include/gpu/GrCaps.h
+++ b/include/gpu/GrCaps.h
@@ -76,6 +76,17 @@ public:
     };
 
     /**
+    * Returns the effective amount of precision found in floating point types with a given precision
+    * qualifier.
+    *
+    *  e.g. If lowp == mediump, effectiveFloatPrecision(lowp) is mediump.
+    *       If the platform doesn't use precision, effectiveFloatPrecision() is always highp.
+    */
+    GrSLPrecision effectiveFloatPrecision(GrShaderType shaderType, GrSLPrecision precision) const {

[bsalomon, 2016/04/06 13:35:56]

It still feels odd to me that we have a precooked table with SLPrecision values
for PixelConfigs. Are they based on the min specifications for precision
qualifiers in the ES2 spec? That would make me feel better about it. But then
I'd also think that it shouldn't be a global function but backend dependent
(that is, make this function take the config rather than a precision from a
global table).

+        return fEffectiveFloatPrecisions[shaderType][precision];
+    }
+
+    /**
     * Is there any difference between the float shader variable precision types? If this is true
     * then unless the shader type is not supported, any call to getFloatShaderPrecisionInfo() would
     * report the same info for all precisions in all shader types.
@@ -101,6 +112,9 @@ public:
     }
 
 protected:
+    /** Subclasses must call this after filling in the shader precision table. */
+    void initEffectiveFloatPrecisionTable();
+
     /** Subclasses must call this after initialization in order to apply caps overrides requested by
         the client. Note that overrides will only reduce the caps never expand them. */
     void applyOptionsOverrides(const GrContextOptions& options);
@@ -114,6 +128,7 @@ protected:
 
     bool fShaderPrecisionVaries;
     PrecisionInfo fFloatPrecisions[kGrShaderTypeCount][kGrSLPrecisionCount];
+    GrSLPrecision fEffectiveFloatPrecisions[kGrShaderTypeCount][kGrSLPrecisionCount];
     int fPixelLocalStorageSize;
     bool fPLSPathRenderingSupport;