Add GrCap for initializing textures

Change-Id: Ifdf50c6686a3369a00cc15fa868a4807f0898fd6
Bug: skia:8378
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/204266
Reviewed-by: Robert Phillips <robertphillips@google.com>
Commit-Queue: Kevin Lubick <kjlubick@google.com>

src/gpu/GrCaps.cpp

@@ -33,6 +33,7 @@ GrCaps::GrCaps(const GrContextOptions& options) {
     fPreferClientSideDynamicBuffers = false;
     fPreferFullscreenClears = false;
     fMustClearUploadedBufferData = false;
+    fShouldInitializeTextures = false;
     fSupportsAHardwareBufferImages = false;
     fFenceSyncSupport = false;
     fCrossContextTextureSupport = false;
@@ -198,6 +199,7 @@ void GrCaps::dumpJSON(SkJSONWriter* writer) const {
     writer->appendBool("Prefer client-side dynamic buffers", fPreferClientSideDynamicBuffers);
     writer->appendBool("Prefer fullscreen clears", fPreferFullscreenClears);
     writer->appendBool("Must clear buffer memory", fMustClearUploadedBufferData);
+    writer->appendBool("Should initialize textures", fShouldInitializeTextures);
     writer->appendBool("Supports importing AHardwareBuffers", fSupportsAHardwareBufferImages);
     writer->appendBool("Fence sync support", fFenceSyncSupport);
     writer->appendBool("Cross context texture support", fCrossContextTextureSupport);

src/gpu/GrCaps.h

@@ -233,6 +233,13 @@ public:
         is not initialized (even if not read by draw calls). */
     bool mustClearUploadedBufferData() const { return fMustClearUploadedBufferData; }
 
+    /** For some environments, there is a performance or safety concern to not
+        initializing textures. For example, with WebGL and Firefox, there is a large
+        performance hit to not doing it.
+     */
+    bool shouldInitializeTextures() const { return fShouldInitializeTextures; }
+
+
     /** Returns true if the given backend supports importing AHardwareBuffers via the
      * GrAHardwarebufferImageGenerator. This will only ever be supported on Android devices with API
      * level >= 26.
@@ -345,6 +352,7 @@ protected:
     bool fPreferClientSideDynamicBuffers             : 1;
     bool fPreferFullscreenClears                     : 1;
     bool fMustClearUploadedBufferData                : 1;
+    bool fShouldInitializeTextures                   : 1;
     bool fSupportsAHardwareBufferImages              : 1;
     bool fHalfFloatVertexAttributeSupport            : 1;
     bool fClampToBorderSupport                       : 1;

src/gpu/gl/GrGLCaps.cpp

@@ -536,6 +536,16 @@ void GrGLCaps::init(const GrContextOptions& contextOptions,
         fMustClearUploadedBufferData = true;
     }
 
+    // In a WASM build on Firefox, we see warnings like
+    // WebGL warning: texSubImage2D: This operation requires zeroing texture data. This is slow.
+    // WebGL warning: texSubImage2D: Texture has not been initialized prior to a partial upload,
+    //                forcing the browser to clear it. This may be slow.
+    // Setting the initial clear seems to make those warnings go away and offers a substantial
+    // boost in performance in Firefox. Chrome sees a more modest increase.
+    if (kIsWebGL) {
+        fShouldInitializeTextures = true;
+    }
+
     if (GR_IS_GR_GL(standard)) {
         // ARB allows mixed size FBO attachments, EXT does not.
         if (version >= GR_GL_VER(3, 0) ||