[Development] VSync problems (tearing)

[gunnar.sletta at nokia.com]

On Jun 14, 2012, at 10:39 AM, ext Dietrich.Gossen at conti-engineering.com wrote:

> Hi,
> The vsync problems in Qt 5 Alpha are still there. I am using the eglfs plugin on an i.MX board. 
> Although the performance is ok, tearing is visible. The new threading model of scenegraph was supposed to fix this, wasn’t it?

> Is this maybe a eglfs plugin problem?

The threaded renderloop doesn't really affect tearing. We call QOpenGLContext::swapBuffers() which turns into eglSwapBuffers() inside the eglfs plugin. If that tears, then it is because:
1. eglSwapInterval has not been set to 1 (indicating that buffer presentation to screen should happen in sync with vsync) or
2. The GL driver does not support tearfree graphics.

If you can run a stand alone OpenGL app and it does not tear, then the problem is most likely related to 1.

cheers,
Gunnar