Make GrCaps::surfaceSupportsReadPixels return distinct values rather than flags.

Change-Id: I2744ca6cb0e9f1f2fd7d20e293400c788e7d4083
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/224960
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>

src/gpu/GrCaps.h

@@ -204,24 +204,29 @@ public:
      */
     bool surfaceSupportsWritePixels(const GrSurface*) const;
 
-
     /**
-     * Indicates whether surface supports readPixels or the alternatives.
+     * Indicates whether surface supports GrGpu::readPixels, must be copied, or cannot be read.
      */
-    enum ReadFlags {
-        kSupported_ReadFlag     = 0x0,
-        kRequiresCopy_ReadFlag  = 0x1,
-        kProtected_ReadFlag     = 0x2,
+    enum class SurfaceReadPixelsSupport {
+        /** GrGpu::readPixels is supported by the surface. */
+        kSupported,
+        /**
+         * GrGpu::readPixels is not supported by this surface but this surface can be drawn
+         * or copied to a Ganesh-created GrTextureType::kTexture2D and then that surface will be
+         * readable.
+         */
+        kCopyToTexture2D,
+        /**
+         * Not supported
+         */
+        kUnsupported,
     };
-
     /**
-     * Backends may have restrictions on what types of surfaces support GrGpu::readPixels().
-     * If this returns kRequiresCopy_ReadFlag then the caller should implement a fallback where a
-     * temporary texture is created, the surface is drawn or copied into the temporary, and
-     * pixels are read from the temporary. If this returns kProtected_ReadFlag, then the caller
-     * should not attempt reading it.
+     * Backends may have restrictions on what types of surfaces support GrGpu::readPixels(). We may
+     * either be able to read directly from the surface, read from a copy of the surface, or not
+     * read at all.
      */
-    virtual ReadFlags surfaceSupportsReadPixels(const GrSurface*) const = 0;
+    virtual SurfaceReadPixelsSupport surfaceSupportsReadPixels(const GrSurface*) const = 0;
 
     /**
      * Given a dst pixel config and a src color type what color type must the caller coax the

src/gpu/GrSurfaceContext.cpp

@@ -119,11 +119,11 @@ bool GrSurfaceContext::readPixels(const GrPixelInfo& origDstInfo, void* dst, siz
                             direct->priv().validPMUPMConversionExists();
 
     auto readFlag = caps->surfaceSupportsReadPixels(srcSurface);
-    if (readFlag == GrCaps::kProtected_ReadFlag) {
+    if (readFlag == GrCaps::SurfaceReadPixelsSupport::kUnsupported) {
         return false;
     }
 
-    if (readFlag == GrCaps::kRequiresCopy_ReadFlag || canvas2DFastPath) {
+    if (readFlag == GrCaps::SurfaceReadPixelsSupport::kCopyToTexture2D || canvas2DFastPath) {
         GrBackendFormat format;
         GrPixelConfig config;
         GrColorType colorType;

src/gpu/gl/GrGLCaps.cpp

@@ -3392,15 +3392,16 @@ bool GrGLCaps::onSurfaceSupportsWritePixels(const GrSurface* surface) const {
     return true;
 }
 
-GrCaps::ReadFlags GrGLCaps::surfaceSupportsReadPixels(const GrSurface* surface) const {
+GrCaps::SurfaceReadPixelsSupport GrGLCaps::surfaceSupportsReadPixels(
+        const GrSurface* surface) const {
     if (auto tex = static_cast<const GrGLTexture*>(surface->asTexture())) {
         // We don't support reading pixels directly from EXTERNAL textures as it would require
         // binding the texture to a FBO.
         if (tex->target() == GR_GL_TEXTURE_EXTERNAL) {
-            return kRequiresCopy_ReadFlag;
+            return SurfaceReadPixelsSupport::kCopyToTexture2D;
         }
     }
-    return kSupported_ReadFlag;
+    return SurfaceReadPixelsSupport::kSupported;
 }
 
 GrCaps::SupportedRead GrGLCaps::supportedReadPixelsColorType(GrPixelConfig srcPixelConfig,

src/gpu/gl/GrGLCaps.h

@@ -320,7 +320,7 @@ public:
     /// Use indices or vertices in CPU arrays rather than VBOs for dynamic content.
     bool useNonVBOVertexAndIndexDynamicData() const { return fUseNonVBOVertexAndIndexDynamicData; }
 
-    ReadFlags surfaceSupportsReadPixels(const GrSurface*) const override;
+    SurfaceReadPixelsSupport surfaceSupportsReadPixels(const GrSurface*) const override;
     SupportedRead supportedReadPixelsColorType(GrPixelConfig, const GrBackendFormat&,
                                                GrColorType) const override;
 

src/gpu/mock/GrMockCaps.h

@@ -110,8 +110,8 @@ public:
         return 0;
     }
 
-    ReadFlags surfaceSupportsReadPixels(const GrSurface*) const override {
-        return kSupported_ReadFlag;
+    SurfaceReadPixelsSupport surfaceSupportsReadPixels(const GrSurface*) const override {
+        return SurfaceReadPixelsSupport::kSupported;
     }
 
     bool initDescForDstCopy(const GrRenderTargetProxy* src, GrSurfaceDesc* desc,

src/gpu/mtl/GrMtlCaps.h

@@ -41,8 +41,8 @@ public:
     int maxRenderTargetSampleCount(SkColorType, const GrBackendFormat&) const override;
     int maxRenderTargetSampleCount(GrPixelConfig) const override;
 
-    ReadFlags surfaceSupportsReadPixels(const GrSurface*) const override {
-        return kSupported_ReadFlag;
+    SurfaceReadPixelsSupport surfaceSupportsReadPixels(const GrSurface*) const override {
+        return SurfaceReadPixelsSupport::kSupported;
     }
 
     bool isFormatCopyable(SkColorType, const GrBackendFormat&) const override { return true; }

src/gpu/vk/GrVkCaps.cpp

@@ -900,17 +900,18 @@ int GrVkCaps::maxRenderTargetSampleCount(VkFormat format) const {
     return table[table.count() - 1];
 }
 
-GrCaps::ReadFlags GrVkCaps::surfaceSupportsReadPixels(const GrSurface* surface) const {
+GrCaps::SurfaceReadPixelsSupport GrVkCaps::surfaceSupportsReadPixels(
+        const GrSurface* surface) const {
     if (surface->isProtected()) {
-        return kProtected_ReadFlag;
+        return SurfaceReadPixelsSupport::kUnsupported;
     }
     if (auto tex = static_cast<const GrVkTexture*>(surface->asTexture())) {
         // We can't directly read from a VkImage that has a ycbcr sampler.
         if (tex->ycbcrConversionInfo().isValid()) {
-            return kRequiresCopy_ReadFlag;
+            return SurfaceReadPixelsSupport::kCopyToTexture2D;
         }
     }
-    return kSupported_ReadFlag;
+    return SurfaceReadPixelsSupport::kSupported;
 }
 
 bool GrVkCaps::onSurfaceSupportsWritePixels(const GrSurface* surface) const {

src/gpu/vk/GrVkCaps.h

@@ -52,7 +52,7 @@ public:
     int maxRenderTargetSampleCount(GrPixelConfig config) const override;
     int maxRenderTargetSampleCount(VkFormat format) const;
 
-    ReadFlags surfaceSupportsReadPixels(const GrSurface*) const override;
+    SurfaceReadPixelsSupport surfaceSupportsReadPixels(const GrSurface*) const override;
 
     bool isFormatTexturableLinearly(VkFormat format) const {
         return SkToBool(FormatInfo::kTextureable_Flag & this->getFormatInfo(format).fLinearFlags);