Fix 4444 on Vulkan devices who don't support RGBA_4444

src/gpu/vk/GrVkCaps.cpp

 /*
  * Copyright 2015 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "GrVkCaps.h"
 
 #include "GrVkUtil.h"
@@ skipping 119 matching lines @@
     glslCaps->fVersionDeclString = "#version 330\n";
 
 
     // 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)) {
             glslCaps->fConfigTextureSwizzle[i] = GrSwizzle::RRRR();
             glslCaps->fConfigOutputSwizzle[i] = GrSwizzle::AAAA();
         } else {
-            glslCaps->fConfigTextureSwizzle[i] = GrSwizzle::RGBA();
+            if (kRGBA_4444_GrPixelConfig == config) {
+                // The vulkan spec does not require R4G4B4A4 to be supported for texturing so we
+                // store the data in a B4G4R4A4 texture and then swizzle it when doing texture reads
+                // or writing to outputs. Since we're not actually changing the data at all, the
+                // only extra work is the swizzle in the shader for all operations.
+                glslCaps->fConfigTextureSwizzle[i] = GrSwizzle::BGRA();
+                glslCaps->fConfigOutputSwizzle[i] = GrSwizzle::BGRA();
+            } else {
+                glslCaps->fConfigTextureSwizzle[i] = GrSwizzle::RGBA();
+            }
         }
     }
 
     // Vulkan is based off ES 3.0 so the following should all be supported
     glslCaps->fUsesPrecisionModifiers = true;
     glslCaps->fFlatInterpolationSupport = true;
 
     // GrShaderCaps
 
     glslCaps->fShaderDerivativeSupport = true;
@@ skipping 86 matching lines @@
 
 void GrVkCaps::ConfigInfo::init(const GrVkInterface* interface,
                                 VkPhysicalDevice physDev,
                                 VkFormat format) {
     VkFormatProperties props;
     memset(&props, 0, sizeof(VkFormatProperties));
     GR_VK_CALL(interface, GetPhysicalDeviceFormatProperties(physDev, format, &props));
     InitConfigFlags(props.linearTilingFeatures, &fLinearFlags);
     InitConfigFlags(props.optimalTilingFeatures, &fOptimalFlags);
 }