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

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

Index: third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp
diff --git a/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp b/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp
index 70d454fe26280c8b1fb0f5a6742bb196a21fb48d..8e6356a13638a7f9695fd598a3140da876a99d4a 100644
--- a/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp
+++ b/third_party/WebKit/Source/modules/webgl/WebGLRenderingContextBase.cpp
@@ -4145,6 +4145,16 @@ bool WebGLRenderingContextBase::canUseTexImageCanvasByGPU(GLint internalformat,
 {
     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;
 }