877309 - Drawing a webgl canvas to another canvas shows last bound framebuffer

Status: RESOLVED FIXED

(Core :: Graphics: CanvasWebGL, defect)

Description

[Bill Baxter]

Attachment: index.html

User Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/27.0.1453.93 Safari/537.36

Steps to reproduce:

If you are doing offscreen rendering to a texture render target, and don't re-bind the primary framebuffer, then when you do a call like context2d.drawImage(webglCanvas, 0, 0), what you get is a copy of the last bound framebuffer, rather than the content that is actually showing on the WebGL canvas.

This is not the result that the spec leads me to expect.

I have a repro at http://www.billbaxter.com/rttRepro, and also attached.


Actual results:

If you call drawImage with the webgl canvas as the source, you seem to get the last framebuffer bound rather than the primary/screen framebuffer of the webgl canvas.


Expected results:

I think context2d.drawImage should never copy an offscreen framebuffer from a webgl canvas, but rather always the primary framebuffer.

Comment 1

[Bill Baxter]

Note that it seems that Firefox behaves the same whether or not preserveDrawingBuffer is set to true or not.  In the case of preserveDrawingBuffer=false, the spec says you can't count on drawImage working properly unless you do it before returning from your requestAnimationFrame callback.

You can turn preserveDrawingBuffer on in the demo with http://www.billbaxter.com/rttRepro?preserve

Comment 2

[Kelsey Gilbert [:jgilbert]]

Attachment: patch: Read from screen, not current bound FBO for WebGLContext::Render

Yep, oops.

Comment 3

[Bill Baxter]

Nice!  Thanks for the quick fix.

Comment 4

[Kelsey Gilbert [:jgilbert]]

https://hg.mozilla.org/integration/mozilla-inbound/rev/338bb731eb55

Comment 5

[Ed Morley [:emorley]]

https://hg.mozilla.org/mozilla-central/rev/338bb731eb55