Force input coverage to be only a byte in gpu shaders.

include/gpu/GrTypesPriv.h

Index: include/gpu/GrTypesPriv.h
diff --git a/include/gpu/GrTypesPriv.h b/include/gpu/GrTypesPriv.h
index 0bae612db19d68ffbf85337492114dab0ba84170..75c987f148707ab05f659a9b9938d89dc6bab663 100644
--- a/include/gpu/GrTypesPriv.h
+++ b/include/gpu/GrTypesPriv.h
@@ -70,6 +70,8 @@ enum GrVertexAttribType {
     kVec2f_GrVertexAttribType,
     kVec3f_GrVertexAttribType,
     kVec4f_GrVertexAttribType,
+
+    kUByte_GrVertexAttribType,   // unsigned byte, e.g. coverage
     kVec4ub_GrVertexAttribType,   // vector of 4 unsigned bytes, e.g. colors
 
     kLast_GrVertexAttribType = kVec4ub_GrVertexAttribType
@@ -81,14 +83,15 @@ static const int kGrVertexAttribTypeCount = kLast_GrVertexAttribType + 1;
  */
 static inline int GrVertexAttribTypeVectorCount(GrVertexAttribType type) {
     SkASSERT(type >= 0 && type < kGrVertexAttribTypeCount);
-    static const int kCounts[] = { 1, 2, 3, 4, 4 };
+    static const int kCounts[] = { 1, 2, 3, 4, 1, 4 };
     return kCounts[type];
 
     GR_STATIC_ASSERT(0 == kFloat_GrVertexAttribType);
     GR_STATIC_ASSERT(1 == kVec2f_GrVertexAttribType);
     GR_STATIC_ASSERT(2 == kVec3f_GrVertexAttribType);
     GR_STATIC_ASSERT(3 == kVec4f_GrVertexAttribType);
-    GR_STATIC_ASSERT(4 == kVec4ub_GrVertexAttribType);
+    GR_STATIC_ASSERT(4 == kUByte_GrVertexAttribType);
+    GR_STATIC_ASSERT(5 == kVec4ub_GrVertexAttribType);
     GR_STATIC_ASSERT(SK_ARRAY_COUNT(kCounts) == kGrVertexAttribTypeCount);
 }
 
@@ -102,6 +105,7 @@ static inline size_t GrVertexAttribTypeSize(GrVertexAttribType type) {
         2*sizeof(float),        // kVec2f_GrVertexAttribType
         3*sizeof(float),        // kVec3f_GrVertexAttribType
         4*sizeof(float),        // kVec4f_GrVertexAttribType
+        1*sizeof(char),         // kUByte_GrVertexAttribType
         4*sizeof(char)          // kVec4ub_GrVertexAttribType
     };
     return kSizes[type];
@@ -110,7 +114,8 @@ static inline size_t GrVertexAttribTypeSize(GrVertexAttribType type) {
     GR_STATIC_ASSERT(1 == kVec2f_GrVertexAttribType);
     GR_STATIC_ASSERT(2 == kVec3f_GrVertexAttribType);
     GR_STATIC_ASSERT(3 == kVec4f_GrVertexAttribType);
-    GR_STATIC_ASSERT(4 == kVec4ub_GrVertexAttribType);
+    GR_STATIC_ASSERT(4 == kUByte_GrVertexAttribType);
+    GR_STATIC_ASSERT(5 == kVec4ub_GrVertexAttribType);
     GR_STATIC_ASSERT(SK_ARRAY_COUNT(kSizes) == kGrVertexAttribTypeCount);
 }
 
@@ -123,7 +128,7 @@ enum GrVertexAttribBinding {
     kPosition_GrVertexAttribBinding,    // required, must have vector count of 2
     kLocalCoord_GrVertexAttribBinding,  // must have vector count of 2
     kColor_GrVertexAttribBinding,       // must have vector count of 4
-    kCoverage_GrVertexAttribBinding,    // must have vector count of 4
+    kCoverage_GrVertexAttribBinding,    // must have a single byte
 
     kLastFixedFunction_GrVertexAttribBinding = kCoverage_GrVertexAttribBinding,
 
@@ -139,7 +144,7 @@ static const int kGrFixedFunctionVertexAttribBindingCnt =
 
 static inline int GrFixedFunctionVertexAttribVectorCount(GrVertexAttribBinding binding) {
     SkASSERT(binding >= 0 && binding < kGrFixedFunctionVertexAttribBindingCnt);
-    static const int kVecCounts[] = { 2, 2, 4, 4 };
+    static const int kVecCounts[] = { 2, 2, 4, 1 };
 
     return kVecCounts[binding];