522201 - WebGL gl.clear doesn't update canvas if nothing else is drawn

Status: RESOLVED FIXED

(Core :: Graphics: Canvas2D, enhancement)

Description

[00003b]

User-Agent:       Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.3) Gecko/20090910 Ubuntu/9.04 (jaunty) Shiretoko/3.5.3
Build Identifier: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.3a1pre) Gecko/20091013 Minefield/3.7a1pre

calling cl.clear without any other drawing doesn't update the contents of the canvas drawn on the web page

Reproducible: Always

Steps to Reproduce:
1. view attached test case in webgl enabled browser
2. move mouse over webgl canvas area
3.
Actual Results:  
canvas doesn't update from mousemove events, which call gl.Clear, but do update when from mousedown events, which calls drawElements. The mousemove events sometimes do have an effect right after a mousedown event though.

Expected Results:  
canvas is cleared and changes color based on mouse position when mouse is moved over canvas area

I've listed it as 'enhancement' severity, since there isn't a spec available to say which behavior is correct, and it is easy to work around anyway, either by making a 0 element draw call, or just using a quad to clear the screen in the first place. At least 1 other person in addition to me was confused by this when first starting out though, since it is an obvious first thing to try, and seems like it should work.

Comment 1

[00003b]

Attachment: test case

Comment 2

[Mark Steele]

Attachment: set invalidate on clear

Comment 3

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

http://hg.mozilla.org/mozilla-central/rev/e609c57a916d