WebGL with CocoonJS - Duplicate triangle

Question

I have a very simple test code which draws a moving triangle. In Chrome it works fine, however on an Android 4.1 Device with the CocoonJS 1.4.1 launcher (which funnels work to OpenGL ES 2.0) a random effect pops in:

The triangle is drawn, but quite often also a bit translated triangle is also drawn (more exactly, the extra triangle seems to be a replica of a formerly drawn one, but the distance is not consistently the same). The tri needs to be moved with some minimal speed for the effect to show (or maybe the replica is just hidden if moving is slow). The tint of the replica seems to be a bit different (even though the fragment shader color is constant), but it might be some alpha magic.

Other CocoonJS WebGL demos work fine on the device, however they don't exhibit fast movement. OpenGL benchmarks run fine.

Drawing multiple triangles has the same effect. Even though gl.Clear is used, it seems like part of some previous buffer shines through. Have you seen anything similar? Any ideas?

Answer 1

Thank you so much for your report, this is a known bug and we are working to solve this issue.

btw, by changing the setInverval time to this one: setInterval(loop, 16); should solve the problem temporarily.