681791 - When trying to create a too large canvas, don't throw, instead just use a smaller drawing buffer

Status: RESOLVED FIXED

(Core :: Graphics: CanvasWebGL, defect)

Description

[Benoit Jacob [:bjacob] (mostly away)]

We currently file a few WebGL conformance tests, like

https://cvs.khronos.org/svn/repos/registry/trunk/public/webgl/sdk/tests/conformance/canvas/drawingbuffer-static-canvas-test.html

Because we throw on canvas.width = something_huge when SetDimensions fails.

Chrome doesn't throw there.

Chrome also won't use a drawingbuffer larger than the max texture size or 4k, whichever is smaller.

We need to fail less on resizing-canvases-to-large-sizes by using a smaller drawingbuffer if needed.

Comment 1

[Kelsey Gilbert [:jgilbert]]

Attachment: Fixes GLContext::ResizeOffscreen leaving a mess on failure

This change basically guarantees that GLContext will not be changed if a resize attempt fails.

Comment 2

[Kelsey Gilbert [:jgilbert]]

It didn't occur to me before that the arguably time-saving initialize once approach was incompatible with soft-failing resizing.
Updated try: https://tbpl.mozilla.org/?tree=Try&usebuildbot=1&rev=322fe6cae175

Comment 3

[Kelsey Gilbert [:jgilbert]]

Yeah, that didn't work so well. 
Updated:
https://tbpl.mozilla.org/?tree=Try&usebuildbot=1&rev=089d1b13072f

Comment 4

[Kelsey Gilbert [:jgilbert]]

Attachment: Guarantees that GLContext::ResizeOffscreen is harmless if it fails

Current patch file.

Comment 5

[Kelsey Gilbert [:jgilbert]]

Ran into a problem on OS X.

Comment 6

[Kelsey Gilbert [:jgilbert]]

Attachment: Guarantees that GLContext::ResizeOffscreen is harmless if it fails

Fixed CGL impl.

Comment 7

[Kelsey Gilbert [:jgilbert]]

New try run:
https://tbpl.mozilla.org/?tree=Try&rev=5a9f76410202

Comment 8

[Kelsey Gilbert [:jgilbert]]

For some reason my last changes reset. Maybe I reset my patch file somehow.
Updated try with CGL fix:
https://tbpl.mozilla.org/?tree=Try&rev=ff8c9387530d

Comment 9

[Kelsey Gilbert [:jgilbert]]

Attachment: Guarantees that GLContext::ResizeOffscreen is harmless if it fails

Fixed errant tab issues and added further commenting.

Comment 10

[Kelsey Gilbert [:jgilbert]]

Attachment: Guarantees that GLContext::ResizeOffscreen is harmless if it fails

Predicates too-verbose debug printf on mDebugMode.

Comment 11

[Benoit Jacob [:bjacob] (mostly away)]

Comment on attachment 567147 [details] [diff] [review]
Guarantees that GLContext::ResizeOffscreen is harmless if it fails

Review of attachment 567147 [details] [diff] [review]:
-----------------------------------------------------------------

This looks all good!

Just one remark about something to keep in mind. The ClearSafely() call is mega-super-important for security: we must prevent WebGL scripts from reading back uninitialized video memory from a newly resized canvas. In your AA patches, the FBO becomes two separate FBOs, right. So will we need two ClearSafely() calls there?

Comment 12

[Kelsey Gilbert [:jgilbert]]

> Just one remark about something to keep in mind. The ClearSafely() call is
> mega-super-important for security: we must prevent WebGL scripts from
> reading back uninitialized video memory from a newly resized canvas. In your
> AA patches, the FBO becomes two separate FBOs, right. So will we need two
> ClearSafely() calls there?

I will triple-check, but we shouldn't need to. After clearing the draw buffer, the read buffer /may/ be uninitialized, but before any read call is possible, we blit over the cleared draw buffer, clearing the read buffer. Basically, it's only possible to access if you can read it without using GL commands to do so. We could just deliberately blit over the cleared draw buffer, as that should be minimal cost compared to assembling a resized buffer, but it should not be necessary. If it were necessary, there would be other problems with our WebGL restrictions anyways.

Comment 13

[Kelsey Gilbert [:jgilbert]]

Attachment: Guarantees that GLContext::ResizeOffscreen is harmless if it fails

Carrying forward r+ from bjacob after PR_TRUE/FALSE conversion.

Comment 14

[Benoit Jacob [:bjacob] (mostly away)]

http://hg.mozilla.org/integration/mozilla-inbound/rev/8583488f5241

Comment 15

[Benoit Jacob [:bjacob] (mostly away)]

Re-landed with proper commit message (sorry, should have checked that)
http://hg.mozilla.org/integration/mozilla-inbound/rev/716915ed489c

Comment 16

[Marco Bonardo [:mak]]

https://hg.mozilla.org/mozilla-central/rev/716915ed489c