Fill in missing GrMtlCaps functions and fix for 0 buffer alloc.

Bug: skia:
Change-Id: I4981e49dc45d607f3f6493da67844b6dfa74a551
Reviewed-on: https://skia-review.googlesource.com/c/189493
Commit-Queue: Greg Daniel <egdaniel@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>

src/gpu/mtl/GrMtlBuffer.mm

@@ -36,7 +36,7 @@ GrMtlBuffer::GrMtlBuffer(GrMtlGpu* gpu, size_t size, GrGpuBufferType intendedTyp
     fIsDynamic = false;
 
     // The managed resource mode is only available for macOS. iOS should use shared.
-    fMtlBuffer =
+    fMtlBuffer = size == 0 ? nil :
             [gpu->device() newBufferWithLength: size
                                        options: !fIsDynamic ? MTLResourceStorageModePrivate
 #ifdef SK_BUILD_FOR_MAC

src/gpu/mtl/GrMtlCaps.h

@@ -63,17 +63,11 @@ public:
     }
 
     GrPixelConfig validateBackendRenderTarget(const GrBackendRenderTarget&,
-                                              SkColorType) const override {
+                                              SkColorType) const override;
-        return kUnknown_GrPixelConfig;
-    }
 
-    GrPixelConfig getConfigFromBackendFormat(const GrBackendFormat&, SkColorType) const override {
+    GrPixelConfig getConfigFromBackendFormat(const GrBackendFormat&, SkColorType) const override;
-        return kUnknown_GrPixelConfig;
-    }
 
-    GrPixelConfig getYUVAConfigFromBackendFormat(const GrBackendFormat&) const override {
+    GrPixelConfig getYUVAConfigFromBackendFormat(const GrBackendFormat&) const override;
-        return kUnknown_GrPixelConfig;
-    }
 
     GrBackendFormat getBackendFormatFromGrColorType(GrColorType ct,
                                                     GrSRGBEncoded srgbEncoded) const override;

src/gpu/mtl/GrMtlCaps.mm

@@ -423,6 +423,129 @@ void GrMtlCaps::initStencilFormat(id<MTLDevice> physDev) {
     fPreferredStencilFormat = StencilFormat{ MTLPixelFormatStencil8, 8, 8, true };
 }
 
+GrPixelConfig validate_sized_format(GrMTLPixelFormat grFormat, SkColorType ct) {
+    MTLPixelFormat format = static_cast<MTLPixelFormat>(grFormat);
+    switch (ct) {
+        case kUnknown_SkColorType:
+            return kUnknown_GrPixelConfig;
+        case kAlpha_8_SkColorType:
+            if (MTLPixelFormatA8Unorm == format) {
+                return kAlpha_8_as_Alpha_GrPixelConfig;
+            } else if (MTLPixelFormatR8Unorm == format) {
+                return kAlpha_8_as_Red_GrPixelConfig;
+            }
+            break;
+#ifdef SK_BUILD_FOR_MAC
+        case kRGB_565_SkColorType:
+        case kARGB_4444_SkColorType:
+            return kUnknown_GrPixelConfig;
+            break;
+#else
+        case kRGB_565_SkColorType:
+            if (MTLPixelFormatB5G6R5Unorm == format) {
+                return kRGB_565_GrPixelConfig;
+            }
+            break;
+        case kARGB_4444_SkColorType:
+            if (MTLPixelFormatABGR4Unorm == format) {
+                return kRGBA_4444_GrPixelConfig;
+            }
+            break;
+#endif
+        case kRGBA_8888_SkColorType:
+            if (MTLPixelFormatRGBA8Unorm == format) {
+                return kRGBA_8888_GrPixelConfig;
+            } else if (MTLPixelFormatRGBA8Unorm_sRGB == format) {
+                return kSRGBA_8888_GrPixelConfig;
+            }
+            break;
+        case kRGB_888x_SkColorType:
+            break;
+        case kBGRA_8888_SkColorType:
+            if (MTLPixelFormatBGRA8Unorm == format) {
+                return kBGRA_8888_GrPixelConfig;
+            } else if (MTLPixelFormatBGRA8Unorm_sRGB == format) {
+                return kSBGRA_8888_GrPixelConfig;
+            }
+            break;
+        case kRGBA_1010102_SkColorType:
+            if (MTLPixelFormatRGB10A2Unorm == format) {
+                return kRGBA_1010102_GrPixelConfig;
+            }
+            break;
+        case kRGB_101010x_SkColorType:
+            break;
+        case kGray_8_SkColorType:
+            if (MTLPixelFormatR8Unorm == format) {
+                return kGray_8_as_Red_GrPixelConfig;
+            }
+            break;
+        case kRGBA_F16_SkColorType:
+            if (MTLPixelFormatRG16Float == format) {
+                return kRGBA_half_GrPixelConfig;
+            }
+            break;
+        case kRGBA_F32_SkColorType:
+            if (MTLPixelFormatR32Float == format) {
+                return kRGBA_float_GrPixelConfig;
+            }
+            break;
+    }
+
+    return kUnknown_GrPixelConfig;
+}
+
+GrPixelConfig GrMtlCaps::validateBackendRenderTarget(const GrBackendRenderTarget& rt,
+                                                     SkColorType ct) const {
+    GrMtlTextureInfo fbInfo;
+    if (!rt.getMtlTextureInfo(&fbInfo)) {
+        return kUnknown_GrPixelConfig;
+    }
+
+    id<MTLTexture> texture = (__bridge id<MTLTexture>)fbInfo.fTexture;
+    return validate_sized_format(texture.pixelFormat, ct);
+}
+
+GrPixelConfig GrMtlCaps::getConfigFromBackendFormat(const GrBackendFormat& format,
+                                                    SkColorType ct) const {
+    const GrMTLPixelFormat* mtlFormat = format.getMtlFormat();
+    if (!mtlFormat) {
+        return kUnknown_GrPixelConfig;
+    }
+    return validate_sized_format(*mtlFormat, ct);
+}
+
+static GrPixelConfig get_yuva_config(GrMTLPixelFormat grFormat) {
+    MTLPixelFormat format = static_cast<MTLPixelFormat>(grFormat);
+
+    switch (format) {
+        case MTLPixelFormatA8Unorm:
+            return kAlpha_8_as_Alpha_GrPixelConfig;
+            break;
+        case MTLPixelFormatR8Unorm:
+            return kAlpha_8_as_Red_GrPixelConfig;
+            break;
+        // TODO: Add RG_88 format here
+        case MTLPixelFormatRGBA8Unorm:
+            return kRGBA_8888_GrPixelConfig;
+            break;
+        case MTLPixelFormatBGRA8Unorm:
+            return kBGRA_8888_GrPixelConfig;
+            break;
+        default:
+            return kUnknown_GrPixelConfig;
+            break;
+    }
+}
+
+GrPixelConfig GrMtlCaps::getYUVAConfigFromBackendFormat(const GrBackendFormat& format) const {
+    const GrMTLPixelFormat* mtlFormat = format.getMtlFormat();
+    if (!mtlFormat) {
+        return kUnknown_GrPixelConfig;
+    }
+    return get_yuva_config(*mtlFormat);
+}
+
 GrBackendFormat GrMtlCaps::getBackendFormatFromGrColorType(GrColorType ct,
                                                            GrSRGBEncoded srgbEncoded) const {
     GrPixelConfig config = GrColorTypeToPixelConfig(ct, srgbEncoded);