Upload textures through GPU path to non-8-bit color formats won't work in WebGL2

third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp

 /*
  * Copyright (C) 2009 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
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@@ skipping 4127 matching lines @@
         // The UNSIGNED_INT_10F_11F_11F_REV type pack/unpack isn't implemented.
         type = GL_FLOAT;
     }
     texImage2DImpl(target, level, internalformat, format, type, imageForRender.get(), WebGLImageConversion::HtmlDomImage, m_unpackFlipY, m_unpackPremultiplyAlpha);
 }
 
 bool WebGLRenderingContextBase::canUseTexImageCanvasByGPU(GLint internalformat, GLenum type)
 {
     if (isFloatType(type) || isIntegerFormat(internalformat) || isSRGBFormat(internalformat))
         return false;
+    switch (internalformat) {
+    case GL_RGB565:
+    case GL_RGBA4:
+    case GL_RGB5_A1:

[Zhenyao Mo, 2016/06/06 12:47:47]

I think these are the only packed formats that goes down the gpu path.

[Corentin Wallez, 2016/06/06 15:25:46]

What is the alternative path?

[Zhenyao Mo, 2016/06/06 16:09:20]

We pack them into target format in software and then just simple tex{Sub}Image,
so no copyTexImage op.

+        // FIXME: ES3 limitation that CopyTexImage with sized internalformat,
+        // component sizes have to match the source color format.

[Ken Russell (switch to Gerrit), 2016/06/06 23:23:48]

Do you think it would be worth making canUseTexImageCanvasByGPU virtual, and
adding this rule in WebGL2RenderingContextBase's version?

I realize this is intended as a temporary workaround. However, there may be a
general problem with handling these packed formats. We've found that some of
these texture formats are not renderable on OS X. If we also can't do
CopyTexImage2D from an RGBA8 texture to one of these packed formats, then we
have no way to do a GPU-GPU copy into these packed formats.

[Zhenyao Mo, 2016/06/07 00:36:50]

Done.  RGB565 is only not renderable on Mac NVidia, which seems more like a
driver bug to me.

+        return false;
+    default:
+        break;
+    }
     return true;
 }
 
 void WebGLRenderingContextBase::texImageCanvasByGPU(TexImageByGPUType functionType, WebGLTexture* texture, GLenum target,
     GLint level, GLint internalformat, GLenum type, GLint xoffset, GLint yoffset, GLint zoffset, HTMLCanvasElement* canvas)
 {
     ScopedTexture2DRestorer restorer(this);
 
     GLuint targetTexture = texture->object();
     GLenum targetType = type;
@@ skipping 2266 matching lines @@
         contextGL()->PixelStorei(GL_UNPACK_ALIGNMENT, 1);
 }
 
 void WebGLRenderingContextBase::restoreUnpackParameters()
 {
     if (m_unpackAlignment != 1)
         contextGL()->PixelStorei(GL_UNPACK_ALIGNMENT, m_unpackAlignment);
 }
 
 } // namespace blink