Add private grpixelconfigs for alpha_8 and alpha_half

Bug: skia:
Change-Id: I5191b6e045aea2a5af2b305b5972ad1e638a7ace
Reviewed-on: https://skia-review.googlesource.com/71763
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>

14 files changed, 194 insertions, 72 deletions

diff --git a/include/gpu/GrTypes.h b/include/gpu/GrTypes.h
index 57f32f2504..c47cfc8f86 100644
--- a/include/gpu/GrTypes.h
+++ b/include/gpu/GrTypes.h
@@ -343,7 +343,12 @@ enum GrPixelConfig {
     */
     kRGBA_half_GrPixelConfig,
 
-    kLast_GrPixelConfig = kRGBA_half_GrPixelConfig
+    kPrivateConfig1_GrPixelConfig,
+    kPrivateConfig2_GrPixelConfig,
+    kPrivateConfig3_GrPixelConfig,
+    kPrivateConfig4_GrPixelConfig,
+
+    kLast_GrPixelConfig = kPrivateConfig4_GrPixelConfig
 };
 static const int kGrPixelConfigCnt = kLast_GrPixelConfig + 1;
 
diff --git a/include/gpu/mock/GrMockTypes.h b/include/gpu/mock/GrMockTypes.h
index 3ad0fc3b9a..35bb5efe23 100644
--- a/include/gpu/mock/GrMockTypes.h
+++ b/include/gpu/mock/GrMockTypes.h
@@ -9,6 +9,7 @@
 #define GrMockOptions_DEFINED
 
 #include "GrTypes.h"
+#include "../private/GrTypesPriv.h"
 
 struct GrMockTextureInfo {
     int fID;
@@ -25,6 +26,8 @@ struct GrMockOptions {
         fConfigOptions[kRGBA_8888_GrPixelConfig].fRenderable[0] = true;
         fConfigOptions[kRGBA_8888_GrPixelConfig].fTexturable = true;
         fConfigOptions[kAlpha_8_GrPixelConfig].fTexturable = true;
+        fConfigOptions[kAlpha_8_as_Alpha_GrPixelConfig].fTexturable = true;
+        fConfigOptions[kAlpha_8_as_Red_GrPixelConfig].fTexturable = true;
         fConfigOptions[kRGB_565_GrPixelConfig].fTexturable = true;
     }
 
diff --git a/include/private/GrTypesPriv.h b/include/private/GrTypesPriv.h
index 9922f4cbc0..9f379f6efb 100644
--- a/include/private/GrTypesPriv.h
+++ b/include/private/GrTypesPriv.h
@@ -801,6 +801,15 @@ enum class  GrMipMapsStatus {
 GR_MAKE_BITFIELD_CLASS_OPS(GpuPathRenderers)
 
 /**
+ * We want to extend the GrPixelConfig enum to add cases for dealing with alpha_8 which is
+ * internally either alpha8 or red8
+ */
+static constexpr GrPixelConfig kAlpha_8_as_Alpha_GrPixelConfig = kPrivateConfig1_GrPixelConfig;
+static constexpr GrPixelConfig kAlpha_8_as_Red_GrPixelConfig = kPrivateConfig2_GrPixelConfig;
+static constexpr GrPixelConfig kAlpha_half_as_Alpha_GrPixelConfig = kPrivateConfig3_GrPixelConfig;
+static constexpr GrPixelConfig kAlpha_half_as_Red_GrPixelConfig = kPrivateConfig4_GrPixelConfig;
+
+/**
  * Utility functions for GrPixelConfig
  */
 // Returns true if the pixel config is 32 bits per pixel
@@ -813,6 +822,8 @@ static inline bool GrPixelConfigIs8888Unorm(GrPixelConfig config) {
             return true;
         case kUnknown_GrPixelConfig:
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kGray_8_GrPixelConfig:
         case kRGB_565_GrPixelConfig:
         case kRGBA_4444_GrPixelConfig:
@@ -820,6 +831,8 @@ static inline bool GrPixelConfigIs8888Unorm(GrPixelConfig config) {
         case kRGBA_float_GrPixelConfig:
         case kRG_float_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
         case kRGBA_half_GrPixelConfig:
             return false;
     }
@@ -836,6 +849,8 @@ static inline bool GrPixelConfigIsSRGB(GrPixelConfig config) {
             return true;
         case kUnknown_GrPixelConfig:
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kGray_8_GrPixelConfig:
         case kRGB_565_GrPixelConfig:
         case kRGBA_4444_GrPixelConfig:
@@ -845,6 +860,8 @@ static inline bool GrPixelConfigIsSRGB(GrPixelConfig config) {
         case kRGBA_float_GrPixelConfig:
         case kRG_float_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
         case kRGBA_half_GrPixelConfig:
             return false;
     }
@@ -866,6 +883,8 @@ static inline GrPixelConfig GrPixelConfigSwapRAndB(GrPixelConfig config) {
             return kSBGRA_8888_GrPixelConfig;
         case kUnknown_GrPixelConfig:
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kGray_8_GrPixelConfig:
         case kRGB_565_GrPixelConfig:
         case kRGBA_4444_GrPixelConfig:
@@ -873,6 +892,8 @@ static inline GrPixelConfig GrPixelConfigSwapRAndB(GrPixelConfig config) {
         case kRGBA_float_GrPixelConfig:
         case kRG_float_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
         case kRGBA_half_GrPixelConfig:
             return kUnknown_GrPixelConfig;
     }
@@ -883,11 +904,15 @@ static inline GrPixelConfig GrPixelConfigSwapRAndB(GrPixelConfig config) {
 static inline size_t GrBytesPerPixel(GrPixelConfig config) {
     switch (config) {
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kGray_8_GrPixelConfig:
             return 1;
         case kRGB_565_GrPixelConfig:
         case kRGBA_4444_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
             return 2;
         case kRGBA_8888_GrPixelConfig:
         case kBGRA_8888_GrPixelConfig:
@@ -915,8 +940,12 @@ static inline bool GrPixelConfigIsOpaque(GrPixelConfig config) {
         case kRG_float_GrPixelConfig:
             return true;
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kRGBA_4444_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
         case kRGBA_8888_GrPixelConfig:
         case kBGRA_8888_GrPixelConfig:
         case kSRGBA_8888_GrPixelConfig:
@@ -934,7 +963,11 @@ static inline bool GrPixelConfigIsOpaque(GrPixelConfig config) {
 static inline bool GrPixelConfigIsAlphaOnly(GrPixelConfig config) {
     switch (config) {
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
             return true;
         case kUnknown_GrPixelConfig:
         case kGray_8_GrPixelConfig:
@@ -959,10 +992,14 @@ static inline bool GrPixelConfigIsFloatingPoint(GrPixelConfig config) {
         case kRGBA_float_GrPixelConfig:
         case kRG_float_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
         case kRGBA_half_GrPixelConfig:
             return true;
         case kUnknown_GrPixelConfig:
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kGray_8_GrPixelConfig:
         case kRGB_565_GrPixelConfig:
         case kRGBA_4444_GrPixelConfig:
@@ -984,6 +1021,8 @@ static inline bool GrPixelConfigIsSint(GrPixelConfig config) {
 static inline bool GrPixelConfigIsUnorm(GrPixelConfig config) {
     switch (config) {
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kGray_8_GrPixelConfig:
         case kRGB_565_GrPixelConfig:
         case kRGBA_4444_GrPixelConfig:
@@ -994,6 +1033,8 @@ static inline bool GrPixelConfigIsUnorm(GrPixelConfig config) {
             return true;
         case kUnknown_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
         case kRGBA_8888_sint_GrPixelConfig:
         case kRGBA_float_GrPixelConfig:
         case kRG_float_GrPixelConfig:
@@ -1009,5 +1050,4 @@ static inline GrPixelConfigIsClamped GrGetPixelConfigIsClamped(GrPixelConfig con
                                                 : GrPixelConfigIsClamped::kYes;
 }
 
-
 #endif
diff --git a/src/gpu/GrCaps.cpp b/src/gpu/GrCaps.cpp
index 2e25845876..482542be25 100644
--- a/src/gpu/GrCaps.cpp
+++ b/src/gpu/GrCaps.cpp
@@ -14,6 +14,8 @@ static const char* pixel_config_name(GrPixelConfig config) {
     switch (config) {
         case kUnknown_GrPixelConfig: return "Unknown";
         case kAlpha_8_GrPixelConfig: return "Alpha8";
+        case kAlpha_8_as_Alpha_GrPixelConfig: return "Alpha8_asAlpha";
+        case kAlpha_8_as_Red_GrPixelConfig: return "Alpha8_asRed";
         case kGray_8_GrPixelConfig: return "Gray8";
         case kRGB_565_GrPixelConfig: return "RGB565";
         case kRGBA_4444_GrPixelConfig: return "RGBA444";
@@ -25,6 +27,8 @@ static const char* pixel_config_name(GrPixelConfig config) {
         case kRGBA_float_GrPixelConfig: return "RGBAFloat";
         case kRG_float_GrPixelConfig: return "RGFloat";
         case kAlpha_half_GrPixelConfig: return "AlphaHalf";
+        case kAlpha_half_as_Alpha_GrPixelConfig: return "AlphaHalf_asAlpha";
+        case kAlpha_half_as_Red_GrPixelConfig: return "AlphaHalf_asRed";
         case kRGBA_half_GrPixelConfig: return "RGBAHalf";
     }
     SK_ABORT("Invalid pixel config");
diff --git a/src/gpu/GrShaderCaps.cpp b/src/gpu/GrShaderCaps.cpp
index 7e44188074..0a612db335 100644
--- a/src/gpu/GrShaderCaps.cpp
+++ b/src/gpu/GrShaderCaps.cpp
@@ -220,22 +220,24 @@ void GrShaderCaps::initSamplerPrecisionTable() {
         }
 
         uint8_t* table = fSamplerPrecisions[visibility];
-        table[kUnknown_GrPixelConfig]        = lowp;
-        table[kAlpha_8_GrPixelConfig]        = lowp;
-        table[kGray_8_GrPixelConfig]         = lowp;
-        table[kRGB_565_GrPixelConfig]        = lowp;
-        table[kRGBA_4444_GrPixelConfig]      = lowp;
-        table[kRGBA_8888_GrPixelConfig]      = lowp;
-        table[kBGRA_8888_GrPixelConfig]      = lowp;
-        table[kSRGBA_8888_GrPixelConfig]     = lowp;
-        table[kSBGRA_8888_GrPixelConfig]     = lowp;
-        table[kRGBA_8888_sint_GrPixelConfig] = lowp;
-        table[kRGBA_float_GrPixelConfig]     = kHigh_GrSLPrecision;
-        table[kRG_float_GrPixelConfig]       = kHigh_GrSLPrecision;
-        table[kAlpha_half_GrPixelConfig]     = mediump;
-        table[kRGBA_half_GrPixelConfig]      = mediump;
-
-        GR_STATIC_ASSERT(14 == kGrPixelConfigCnt);
+        table[kUnknown_GrPixelConfig]             = lowp;
+        table[kAlpha_8_GrPixelConfig]             = lowp;
+        table[kAlpha_8_as_Alpha_GrPixelConfig]    = lowp;
+        table[kAlpha_8_as_Red_GrPixelConfig]      = lowp;
+        table[kGray_8_GrPixelConfig]              = lowp;
+        table[kRGB_565_GrPixelConfig]             = lowp;
+        table[kRGBA_4444_GrPixelConfig]           = lowp;
+        table[kRGBA_8888_GrPixelConfig]           = lowp;
+        table[kBGRA_8888_GrPixelConfig]           = lowp;
+        table[kSRGBA_8888_GrPixelConfig]          = lowp;
+        table[kSBGRA_8888_GrPixelConfig]          = lowp;
+        table[kRGBA_8888_sint_GrPixelConfig]      = lowp;
+        table[kRGBA_float_GrPixelConfig]          = kHigh_GrSLPrecision;
+        table[kRG_float_GrPixelConfig]            = kHigh_GrSLPrecision;
+        table[kAlpha_half_GrPixelConfig]          = mediump;
+        table[kAlpha_half_as_Alpha_GrPixelConfig] = mediump;
+        table[kAlpha_half_as_Red_GrPixelConfig]   = mediump;
+        table[kRGBA_half_GrPixelConfig]           = mediump;
     }
 }
 
diff --git a/src/gpu/SkGr.cpp b/src/gpu/SkGr.cpp
index 026a7482b4..63d0f260b0 100644
--- a/src/gpu/SkGr.cpp
+++ b/src/gpu/SkGr.cpp
@@ -368,7 +368,9 @@ GrPixelConfig SkImageInfo2GrPixelConfig(const SkImageInfo& info, const GrCaps& c
 bool GrPixelConfigToColorType(GrPixelConfig config, SkColorType* ctOut) {
     SkColorType ct;
     switch (config) {
-        case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_GrPixelConfig: // fall through
+        case kAlpha_8_as_Alpha_GrPixelConfig: // fall through
+        case kAlpha_8_as_Red_GrPixelConfig:
             ct = kAlpha_8_SkColorType;
             break;
         case kGray_8_GrPixelConfig:
diff --git a/src/gpu/effects/GrDitherEffect.fp b/src/gpu/effects/GrDitherEffect.fp
index f2d54cf2eb..22c371ea37 100644
--- a/src/gpu/effects/GrDitherEffect.fp
+++ b/src/gpu/effects/GrDitherEffect.fp
@@ -20,11 +20,15 @@ layout(key) in int rangeType;
                 break;
             case kUnknown_GrPixelConfig:
             case kAlpha_half_GrPixelConfig:
+            case kAlpha_half_as_Alpha_GrPixelConfig:
+            case kAlpha_half_as_Red_GrPixelConfig:
             case kRGBA_8888_sint_GrPixelConfig:
             case kRGBA_float_GrPixelConfig:
             case kRG_float_GrPixelConfig:
             case kRGBA_half_GrPixelConfig:
             case kAlpha_8_GrPixelConfig:
+            case kAlpha_8_as_Alpha_GrPixelConfig:
+            case kAlpha_8_as_Red_GrPixelConfig:
                 return nullptr;
         }
         return std::unique_ptr<GrFragmentProcessor>(new GrDitherEffect(rangeType));
diff --git a/src/gpu/effects/GrDitherEffect.h b/src/gpu/effects/GrDitherEffect.h
index deb20852ca..1b1357baff 100644
--- a/src/gpu/effects/GrDitherEffect.h
+++ b/src/gpu/effects/GrDitherEffect.h
@@ -36,11 +36,15 @@ public:
                 break;
             case kUnknown_GrPixelConfig:
             case kAlpha_half_GrPixelConfig:
+            case kAlpha_half_as_Alpha_GrPixelConfig:
+            case kAlpha_half_as_Red_GrPixelConfig:
             case kRGBA_8888_sint_GrPixelConfig:
             case kRGBA_float_GrPixelConfig:
             case kRG_float_GrPixelConfig:
             case kRGBA_half_GrPixelConfig:
             case kAlpha_8_GrPixelConfig:
+            case kAlpha_8_as_Alpha_GrPixelConfig:
+            case kAlpha_8_as_Red_GrPixelConfig:
                 return nullptr;
         }
         return std::unique_ptr<GrFragmentProcessor>(new GrDitherEffect(rangeType));
diff --git a/src/gpu/gl/GrGLCaps.cpp b/src/gpu/gl/GrGLCaps.cpp
index 2212459e68..f245d0f551 100644
--- a/src/gpu/gl/GrGLCaps.cpp
+++ b/src/gpu/gl/GrGLCaps.cpp
@@ -1947,33 +1947,46 @@ void GrGLCaps::initConfigTable(const GrContextOptions& contextOptions,
     }
     fConfigTable[kRGBA_4444_GrPixelConfig].fSwizzle = GrSwizzle::RGBA();
 
-    fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fExternalType = GR_GL_UNSIGNED_BYTE;
-    fConfigTable[kAlpha_8_GrPixelConfig].fFormatType = kNormalizedFixedPoint_FormatType;
-    fConfigTable[kAlpha_8_GrPixelConfig].fFlags = ConfigInfo::kTextureable_Flag;
+    ConfigInfo& alphaInfo = fConfigTable[kAlpha_8_as_Alpha_GrPixelConfig];
+    alphaInfo.fFormats.fExternalType = GR_GL_UNSIGNED_BYTE;
+    alphaInfo.fFormatType = kNormalizedFixedPoint_FormatType;
+    if (kGL_GrGLStandard== standard || version <= GR_GL_VER(3, 0)) {
+        alphaInfo.fFlags = ConfigInfo::kTextureable_Flag;
+    }
+    alphaInfo.fFormats.fBaseInternalFormat = GR_GL_ALPHA;
+    alphaInfo.fFormats.fSizedInternalFormat = GR_GL_ALPHA8;
+    alphaInfo.fFormats.fExternalFormat[kOther_ExternalFormatUsage] = GR_GL_ALPHA;
+    alphaInfo.fSwizzle = GrSwizzle::AAAA();
+    if (fAlpha8IsRenderable && kGL_GrGLStandard== standard) {
+        alphaInfo.fFlags |= allRenderFlags;
+    }
+
+    ConfigInfo& redInfo = fConfigTable[kAlpha_8_as_Red_GrPixelConfig];
+    redInfo.fFormats.fExternalType = GR_GL_UNSIGNED_BYTE;
+    redInfo.fFormatType = kNormalizedFixedPoint_FormatType;
+    redInfo.fFormats.fBaseInternalFormat = GR_GL_RED;
+    redInfo.fFormats.fSizedInternalFormat = GR_GL_R8;
+    redInfo.fFormats.fExternalFormat[kOther_ExternalFormatUsage] = GR_GL_RED;
+    redInfo.fSwizzle = GrSwizzle::RRRR();
+
+    // ES2 Command Buffer does not allow TexStorage with R8_EXT (so Alpha_8 and Gray_8)
+    if (texStorageSupported && !isCommandBufferES2) {
+        alphaInfo.fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
+        redInfo.fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
+    }
+
     if (this->textureRedSupport()) {
-        fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_RED;
-        fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_R8;
-        fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage] =
-            GR_GL_RED;
-        fConfigTable[kAlpha_8_GrPixelConfig].fSwizzle = GrSwizzle::RRRR();
+        redInfo.fFlags = ConfigInfo::kTextureable_Flag;
         if (texelBufferSupport) {
-            fConfigTable[kAlpha_8_GrPixelConfig].fFlags |= ConfigInfo::kCanUseWithTexelBuffer_Flag;
+            redInfo.fFlags |= ConfigInfo::kCanUseWithTexelBuffer_Flag;
         }
-        fConfigTable[kAlpha_8_GrPixelConfig].fFlags |= allRenderFlags;
+        redInfo.fFlags |= allRenderFlags;
+
+        fConfigTable[kAlpha_8_GrPixelConfig] = redInfo;
     } else {
-        fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_ALPHA;
-        fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_ALPHA8;
-        fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage] =
-            GR_GL_ALPHA;
-        fConfigTable[kAlpha_8_GrPixelConfig].fSwizzle = GrSwizzle::AAAA();
-        if (fAlpha8IsRenderable) {
-            fConfigTable[kAlpha_8_GrPixelConfig].fFlags |= allRenderFlags;
-        }
-    }
+        redInfo.fFlags = 0;
 
-    // ES2 Command Buffer does not allow TexStorage with R8_EXT (so Alpha_8 and Gray_8)
-    if (texStorageSupported && !isCommandBufferES2) {
-        fConfigTable[kAlpha_8_GrPixelConfig].fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
+        fConfigTable[kAlpha_8_GrPixelConfig] = alphaInfo;
     }
 
     fConfigTable[kGray_8_GrPixelConfig].fFormats.fExternalType = GR_GL_UNSIGNED_BYTE;
@@ -2068,44 +2081,60 @@ void GrGLCaps::initConfigTable(const GrContextOptions& contextOptions,
         fConfigTable[fpconfig].fSwizzle = GrSwizzle::RGBA();
     }
 
-    if (this->textureRedSupport()) {
-        fConfigTable[kAlpha_half_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_RED;
-        fConfigTable[kAlpha_half_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_R16F;
-        fConfigTable[kAlpha_half_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage]
-            = GR_GL_RED;
-        fConfigTable[kAlpha_half_GrPixelConfig].fSwizzle = GrSwizzle::RRRR();
-        if (texelBufferSupport) {
-            fConfigTable[kAlpha_half_GrPixelConfig].fFlags |=
-                ConfigInfo::kCanUseWithTexelBuffer_Flag;
-        }
-    } else {
-        fConfigTable[kAlpha_half_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_ALPHA;
-        fConfigTable[kAlpha_half_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_ALPHA16F;
-        fConfigTable[kAlpha_half_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage]
-            = GR_GL_ALPHA;
-        fConfigTable[kAlpha_half_GrPixelConfig].fSwizzle = GrSwizzle::AAAA();
-    }
-
+    GrGLenum alphaHalfExternalType;
     if (kGL_GrGLStandard == ctxInfo.standard() || ctxInfo.version() >= GR_GL_VER(3, 0)) {
-        fConfigTable[kAlpha_half_GrPixelConfig].fFormats.fExternalType = GR_GL_HALF_FLOAT;
+        alphaHalfExternalType = GR_GL_HALF_FLOAT;
     } else {
-        fConfigTable[kAlpha_half_GrPixelConfig].fFormats.fExternalType = GR_GL_HALF_FLOAT_OES;
+        alphaHalfExternalType = GR_GL_HALF_FLOAT_OES;
     }
-    fConfigTable[kAlpha_half_GrPixelConfig].fFormatType = kFloat_FormatType;
+
+    ConfigInfo& alphaHalf = fConfigTable[kAlpha_half_as_Alpha_GrPixelConfig];
+    alphaHalf.fFormats.fExternalType = alphaHalfExternalType;
+    alphaHalf.fFormatType = kFloat_FormatType;
+    alphaHalf.fFormats.fBaseInternalFormat = GR_GL_ALPHA;
+    alphaHalf.fFormats.fSizedInternalFormat = GR_GL_ALPHA16F;
+    alphaHalf.fFormats.fExternalFormat[kOther_ExternalFormatUsage] = GR_GL_ALPHA;
+    alphaHalf.fSwizzle = GrSwizzle::AAAA();
+
+    ConfigInfo& redHalf = fConfigTable[kAlpha_half_as_Red_GrPixelConfig];
+    redHalf.fFormats.fExternalType = alphaHalfExternalType;
+    redHalf.fFormatType = kFloat_FormatType;
+    redHalf.fFormats.fBaseInternalFormat = GR_GL_RED;
+    redHalf.fFormats.fSizedInternalFormat = GR_GL_R16F;
+    redHalf.fFormats.fExternalFormat[kOther_ExternalFormatUsage] = GR_GL_RED;
+    redHalf.fSwizzle = GrSwizzle::RRRR();
+
     if (texStorageSupported) {
-        fConfigTable[kAlpha_half_GrPixelConfig].fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
+        alphaHalf.fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
+        redHalf.fFlags |= ConfigInfo::kCanUseTexStorage_Flag;
     }
     if (hasHalfFPTextures) {
-        fConfigTable[kAlpha_half_GrPixelConfig].fFlags = ConfigInfo::kTextureable_Flag;
-        // ES requires either 3.2 or the combination of EXT_color_buffer_half_float and support for
-        // GL_RED internal format.
+        if (kGL_GrGLStandard == standard || version <= GR_GL_VER(3, 0)) {
+            alphaHalf.fFlags = ConfigInfo::kTextureable_Flag;
+        }
+        redHalf.fFlags = ConfigInfo::kTextureable_Flag;
         if (kGL_GrGLStandard == standard || version >= GR_GL_VER(3, 2) ||
             (this->textureRedSupport() &&
              ctxInfo.hasExtension("GL_EXT_color_buffer_half_float"))) {
-            fConfigTable[kAlpha_half_GrPixelConfig].fFlags |= fpRenderFlags;
+            if (kGL_GrGLStandard == standard) {
+                alphaHalf.fFlags |= fpRenderFlags;
+            }
+            redHalf.fFlags |= fpRenderFlags;
         }
     }
 
+    if (this->textureRedSupport()) {
+        if (texelBufferSupport) {
+            redHalf.fFlags |= ConfigInfo::kCanUseWithTexelBuffer_Flag;
+        }
+
+        fConfigTable[kAlpha_half_GrPixelConfig] = redHalf;
+    } else {
+        redHalf.fFlags = 0;
+
+        fConfigTable[kAlpha_half_GrPixelConfig] = alphaHalf;
+    }
+
     fConfigTable[kRGBA_half_GrPixelConfig].fFormats.fBaseInternalFormat = GR_GL_RGBA;
     fConfigTable[kRGBA_half_GrPixelConfig].fFormats.fSizedInternalFormat = GR_GL_RGBA16F;
     fConfigTable[kRGBA_half_GrPixelConfig].fFormats.fExternalFormat[kOther_ExternalFormatUsage] =
@@ -2157,8 +2186,12 @@ void GrGLCaps::initConfigTable(const GrContextOptions& contextOptions,
     // kAlpha_8_GrPixelConfig. Alpha8 is not a valid signed internal format so we must use the base
     // internal format for that config when doing TexImage calls.
     if(kGalliumLLVM_GrGLRenderer == ctxInfo.renderer()) {
+        SkASSERT(fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fBaseInternalFormat ==
+                 fConfigTable[kAlpha_8_as_Alpha_GrPixelConfig].fFormats.fBaseInternalFormat);
         fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fInternalFormatTexImage =
             fConfigTable[kAlpha_8_GrPixelConfig].fFormats.fBaseInternalFormat;
+        fConfigTable[kAlpha_8_as_Alpha_GrPixelConfig].fFormats.fInternalFormatTexImage =
+            fConfigTable[kAlpha_8_as_Alpha_GrPixelConfig].fFormats.fBaseInternalFormat;
     }
 
     // OpenGL ES 2.0 + GL_EXT_sRGB allows GL_SRGB_ALPHA to be specified as the <format>
diff --git a/src/gpu/gl/GrGLGpu.cpp b/src/gpu/gl/GrGLGpu.cpp
index 3b39b20f0e..ad13516ce6 100644
--- a/src/gpu/gl/GrGLGpu.cpp
+++ b/src/gpu/gl/GrGLGpu.cpp
@@ -785,11 +785,15 @@ bool GrGLGpu::onWritePixels(GrSurface* surface, GrSurfaceOrigin origin,
 static inline GrGLint config_alignment(GrPixelConfig config) {
     switch (config) {
         case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+        case kAlpha_8_as_Red_GrPixelConfig:
         case kGray_8_GrPixelConfig:
             return 1;
         case kRGB_565_GrPixelConfig:
         case kRGBA_4444_GrPixelConfig:
         case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+        case kAlpha_half_as_Red_GrPixelConfig:
         case kRGBA_half_GrPixelConfig:
             return 2;
         case kRGBA_8888_GrPixelConfig:
diff --git a/src/gpu/mtl/GrMtlUtil.mm b/src/gpu/mtl/GrMtlUtil.mm
index 24643669ea..9e6c632638 100644
--- a/src/gpu/mtl/GrMtlUtil.mm
+++ b/src/gpu/mtl/GrMtlUtil.mm
@@ -7,6 +7,8 @@
 
 #include "GrMtlUtil.h"
 
+#include "GrTypesPriv.h"
+
 bool GrPixelConfigToMTLFormat(GrPixelConfig config, MTLPixelFormat* format) {
     MTLPixelFormat dontCare;
     if (!format) {
@@ -45,9 +47,12 @@ bool GrPixelConfigToMTLFormat(GrPixelConfig config, MTLPixelFormat* format) {
 #else
             return false;
 #endif
-        case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_GrPixelConfig: // fall through
+        case kAlpha_8_as_Red_GrPixelConfig:
             *format = MTLPixelFormatR8Unorm;
             return true;
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+            return false;
         case kGray_8_GrPixelConfig:
             *format = MTLPixelFormatR8Unorm;
             return true;
@@ -60,9 +65,12 @@ bool GrPixelConfigToMTLFormat(GrPixelConfig config, MTLPixelFormat* format) {
         case kRGBA_half_GrPixelConfig:
             *format = MTLPixelFormatRGBA16Float;
             return true;
-        case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_GrPixelConfig: // fall through
+        case kAlpha_half_as_Red_GrPixelConfig:
             *format = MTLPixelFormatR16Float;
             return true;
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+            return false;
     }
     SK_ABORT("Unexpected config");
     return false;
diff --git a/src/gpu/vk/GrVkCaps.cpp b/src/gpu/vk/GrVkCaps.cpp
index 2b24205af8..6804aeb22f 100644
--- a/src/gpu/vk/GrVkCaps.cpp
+++ b/src/gpu/vk/GrVkCaps.cpp
@@ -208,7 +208,10 @@ void GrVkCaps::initShaderCaps(const VkPhysicalDeviceProperties& properties, uint
     // fConfigOutputSwizzle will default to RGBA so we only need to set it for alpha only config.
     for (int i = 0; i < kGrPixelConfigCnt; ++i) {
         GrPixelConfig config = static_cast<GrPixelConfig>(i);
-        if (GrPixelConfigIsAlphaOnly(config)) {
+        // Vulkan doesn't support a single channel format stored in alpha.
+        if (GrPixelConfigIsAlphaOnly(config) &&
+            kAlpha_8_as_Alpha_GrPixelConfig != config &&
+            kAlpha_half_as_Alpha_GrPixelConfig != config) {
             shaderCaps->fConfigTextureSwizzle[i] = GrSwizzle::RRRR();
             shaderCaps->fConfigOutputSwizzle[i] = GrSwizzle::AAAA();
         } else {
diff --git a/src/gpu/vk/GrVkUtil.cpp b/src/gpu/vk/GrVkUtil.cpp
index 0ce47cb962..729804bd32 100644
--- a/src/gpu/vk/GrVkUtil.cpp
+++ b/src/gpu/vk/GrVkUtil.cpp
@@ -42,9 +42,12 @@ bool GrPixelConfigToVkFormat(GrPixelConfig config, VkFormat* format) {
             // store the data is if it was B4G4R4A4 and swizzle in shaders
             *format = VK_FORMAT_B4G4R4A4_UNORM_PACK16;
             return true;
-        case kAlpha_8_GrPixelConfig:
+        case kAlpha_8_GrPixelConfig: // fall through
+        case kAlpha_8_as_Red_GrPixelConfig:
             *format = VK_FORMAT_R8_UNORM;
             return true;
+        case kAlpha_8_as_Alpha_GrPixelConfig:
+            return false;
         case kGray_8_GrPixelConfig:
             *format = VK_FORMAT_R8_UNORM;
             return true;
@@ -57,9 +60,12 @@ bool GrPixelConfigToVkFormat(GrPixelConfig config, VkFormat* format) {
         case kRGBA_half_GrPixelConfig:
             *format = VK_FORMAT_R16G16B16A16_SFLOAT;
             return true;
-        case kAlpha_half_GrPixelConfig:
+        case kAlpha_half_GrPixelConfig: // fall through
+        case kAlpha_half_as_Red_GrPixelConfig:
             *format = VK_FORMAT_R16_SFLOAT;
             return true;
+        case kAlpha_half_as_Alpha_GrPixelConfig:
+            return false;
     }
     SK_ABORT("Unexpected config");
     return false;
diff --git a/tests/GrSurfaceTest.cpp b/tests/GrSurfaceTest.cpp
index eff8c2584e..7c0171d2ec 100644
--- a/tests/GrSurfaceTest.cpp
+++ b/tests/GrSurfaceTest.cpp
@@ -82,6 +82,8 @@ DEF_GPUTEST_FOR_ALL_CONTEXTS(GrSurfaceRenderability, reporter, ctxInfo) {
     GrPixelConfig configs[] = {
         kUnknown_GrPixelConfig,
         kAlpha_8_GrPixelConfig,
+        kAlpha_8_as_Alpha_GrPixelConfig,
+        kAlpha_8_as_Red_GrPixelConfig,
         kGray_8_GrPixelConfig,
         kRGB_565_GrPixelConfig,
         kRGBA_4444_GrPixelConfig,
@@ -93,6 +95,8 @@ DEF_GPUTEST_FOR_ALL_CONTEXTS(GrSurfaceRenderability, reporter, ctxInfo) {
         kRGBA_float_GrPixelConfig,
         kRG_float_GrPixelConfig,
         kAlpha_half_GrPixelConfig,
+        kAlpha_half_as_Alpha_GrPixelConfig,
+        kAlpha_half_as_Red_GrPixelConfig,
         kRGBA_half_GrPixelConfig,
     };
     SkASSERT(kGrPixelConfigCnt == SK_ARRAY_COUNT(configs));