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Old 10-29-10, 08:35 AM   #1
Johann Baudy
Registered User
 
Join Date: Oct 2010
Posts: 4
Angry glX VSYNC does not work with ACER GD245HQ

Hi, I'm trying to implement vertical sync using openGL X with an ACER 19" 1920x1080 120Hz GD245HQ.

Please find below my simple GL code for each frame:

glClearColor(0.0, 0.0, 0.0, 1.0);
glClear(GL_COLOR_BUFFER_BIT);
glBegin(GL_QUADS);
if (i_current) {
glVertex2f(-1.0, -1.0);
glVertex2f(-0.1, -1.0);
glVertex2f(-0.1, 1.0);
glVertex2f(-1.0, 1.0);
} else {
glVertex2f( 0.1, -1.0);
glVertex2f( 1.0, -1.0);
glVertex2f( 1.0, 1.0);
glVertex2f( 0.1, 1.0);
}
glEnd();
glFinish();

glXGetVideoSyncSGI(&i_before_count);
glXWaitVideoSyncSGI(2, (i_before_count+1)%2, &i_after_count);
glutSwapBuffers();

Concerning software timings, everything seems to be perfect. glutSwapBuffers() occurs at 119.98 Hz (sqrt(var): 79.74 us). (nvidia-settings also indicates this frequency for refresh rate)

But at screen, I can notice that sw swap (glutSwapBuffers()) is not "aligned" with my screen vsync. I still observe vsync side effects and flickering. Sw sync freq and Hw sync freq seem to be slightly different (clock drift).

I can't reproduce this issue with a Samsung SyncMaster 2233RZ which is also 120Hz but 1680x1050.

I use ubuntu 10.04 with nvidia driver 260.19.12 (GTX 470).

I'm running out of ideas. So I was wondering if this drift can be due to linux nvidia driver in metamode 1920x1080_120.00 (DUAL LINK)?

Any ideas ???

Thanks
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