Add GrMtlUtil class

Currently just adding support functions to go back and forth between
GrPixelConfigs and MTLPixelFormats.

Bug: skia:
Change-Id: I01a7d6877ebed87b87090ac2b920fee45dc0e856
Reviewed-on: https://skia-review.googlesource.com/29080
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>

gn/gpu.gni

@@ -587,6 +587,8 @@ skia_metal_sources = [
   "$_src/gpu/mtl/GrMtlGpu.mm",
   "$_src/gpu/mtl/GrMtlTrampoline.h",
   "$_src/gpu/mtl/GrMtlTrampoline.mm",
+  "$_src/gpu/mtl/GrMtlUtil.h",
+  "$_src/gpu/mtl/GrMtlUtil.mm",
 ]
 
 skia_native_gpu_sources = [

src/gpu/mtl/GrMtlUtil.h

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef GrMtlUtil_DEFINED
+#define GrMtlUtil_DEFINED
+
+#include "GrTypes.h"
+
+#import <Metal/Metal.h>
+
+/**
+ * Returns the Metal texture format for the given GrPixelConfig
+ */
+bool GrPixelConfigToMTLFormat(GrPixelConfig config, MTLPixelFormat* format);
+
+/**
+* Returns the GrPixelConfig for the given Metal texture format
+*/
+GrPixelConfig GrMTLFormatToPixelConfig(MTLPixelFormat format);
+
+
+#endif

src/gpu/mtl/GrMtlUtil.mm

@@ -0,0 +1,103 @@
+/*
+ * Copyright 2017 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "GrMtlUtil.h"
+
+bool GrPixelConfigToMTLFormat(GrPixelConfig config, MTLPixelFormat* format) {
+    MTLPixelFormat dontCare;
+    if (!format) {
+        format = &dontCare;
+    }
+
+    switch (config) {
+        case kUnknown_GrPixelConfig:
+            return false;
+        case kRGBA_8888_GrPixelConfig:
+            *format = MTLPixelFormatRGBA8Unorm;
+            return true;
+        case kBGRA_8888_GrPixelConfig:
+            *format = MTLPixelFormatBGRA8Unorm;
+            return true;
+        case kSRGBA_8888_GrPixelConfig:
+            *format = MTLPixelFormatRGBA8Unorm_sRGB;
+            return true;
+        case kSBGRA_8888_GrPixelConfig:
+            *format = MTLPixelFormatBGRA8Unorm_sRGB;
+            return true;
+        case kRGBA_8888_sint_GrPixelConfig:
+            *format = MTLPixelFormatRGBA8Sint;
+            return true;
+        case kRGB_565_GrPixelConfig:
+#ifdef SK_BUILD_FOR_IOS
+            *format = MTLPixelFormatR5G6B5Unorm;
+            return true;
+#else
+            return false;
+#endif
+        case kRGBA_4444_GrPixelConfig:
+#ifdef SK_BUILD_FOR_IOS
+            *format = MTLPixelFormatABGR4Unorm;
+            return true;
+#else
+            return false;
+#endif
+        case kAlpha_8_GrPixelConfig:
+            *format = MTLPixelFormatR8Unorm;
+            return true;
+        case kGray_8_GrPixelConfig:
+            *format = MTLPixelFormatR8Unorm;
+            return true;
+        case kRGBA_float_GrPixelConfig:
+            *format = MTLPixelFormatRGBA32Float;
+            return true;
+        case kRG_float_GrPixelConfig:
+            *format = MTLPixelFormatRG32Float;
+            return true;
+        case kRGBA_half_GrPixelConfig:
+            *format = MTLPixelFormatRGBA16Float;
+            return true;
+        case kAlpha_half_GrPixelConfig:
+            *format = MTLPixelFormatR16Float;
+            return true;
+    }
+    SkFAIL("Unexpected config");
+    return false;
+}
+
+GrPixelConfig GrMTLFormatToPixelConfig(MTLPixelFormat format) {
+    switch (format) {
+        case MTLPixelFormatRGBA8Unorm:
+            return kRGBA_8888_GrPixelConfig;
+        case MTLPixelFormatBGRA8Unorm:
+            return kBGRA_8888_GrPixelConfig;
+        case MTLPixelFormatRGBA8Unorm_sRGB:
+            return kSRGBA_8888_GrPixelConfig;
+        case MTLPixelFormatBGRA8Unorm_sRGB:
+            return kSBGRA_8888_GrPixelConfig;
+        case MTLPixelFormatRGBA8Sint:
+            return kRGBA_8888_sint_GrPixelConfig;
+#ifdef SK_BUILD_FOR_IOS
+        case MTLPixelFormatB5G6R5Unorm:
+            return kRGB_565_GrPixelConfig;
+        case MTLPixelFormatABGR4Unorm:
+            return kRGBA_4444_GrPixelConfig;
+#endif
+        case MTLPixelFormatR8Unorm:
+            // We currently set this to be Alpha_8 and have no way to go to Gray_8
+            return kAlpha_8_GrPixelConfig;
+        case MTLPixelFormatRGBA32Float:
+            return kRGBA_float_GrPixelConfig;
+        case MTLPixelFormatRG32Float:
+            return kRG_float_GrPixelConfig;
+        case MTLPixelFormatRGBA16Float:
+            return kRGBA_half_GrPixelConfig;
+        case MTLPixelFormatR16Float:
+            return kAlpha_half_GrPixelConfig;
+        default:
+            return kUnknown_GrPixelConfig;
+    }
+}