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Qt5 on iMX6: enable vsync with single framebuffer

Question asked by Federico Wegher on Jul 30, 2015
Latest reply on Aug 25, 2015 by Federico Wegher



I am using SabreSD evaluation kit with Linux BSP ltib-4.1.1, I have cross-compiled Qt5 and running its test applications with success. From documentation I read that the following environment variable can affect both vertical synch and number of framebuffers used:


- FB_MULTI_BUFFER=1, then one framebuffer is used and vsync is disabled

- FB_MULTI_BUFFER=2, then 2 framebuffers are used and vsync is enabled


My LCD is 1024x600@60Hz and framebuffer virtual size is 1024x600 16bpp.


I have two questions:

- in case FB_MULTI_BUFFER=2, I do not see any change in virtual size, it is always 1024x600. Is it correct? I expected fb driver to be asked for twice as vxres or vyres;

- in case FB_MULTI_BUFFER=1, is there any way to enable vsync anyway? I ask that because my specific application requires framebuffer grabbing, so one framebuffer is a requirement.


Thanks for help.