[Interest] Qt5/OMAP4/EGLFS: Strange animation behaviour

Stephan Kanthak stylon at gmx.de
Tue Nov 20 02:10:04 CET 2012

Hi Donald,

On 11/19/2012 10:54 PM, Donald Carr wrote:
> On top of all of this, I saw weird partial updates on all the OMAP SGX
> based devices I tested against Qt 5. I have a beagle board video
> uploaded which shows the screen broken up into 4 discrete quadrants
> which are alternately updated.
I did make good progress this evening :-). The TI demos do all tear. I 
now traced it down to no vsync at all! My assumption was that these 
demos do instead use vsync, but in fact they don't. Only 
OGLES2ChameleonMan did not seem to tear, but I think only by chance, as 
the frame rate it uses to predict animation was almost exactly matching 
3 times the frame update frequency.

I actually tried a couple of things, but finally explicitly waiting for 
VSYNC within the OMAP display subsystem (DSS) does perfectly vsync all 
demos (an now I've proof for the Kindle Fire's 50Hz panel, too :-) )! 
I'll try to test that on qt5/eglfs tomorrow. Unfortunately, in the 
2.6.35 kernel that I'm using OMAP DSS does not yet handle the generic 
FBIO_WAITFORVSYNC, but instead uses own ioctls. I've seen that more 
recent omap kernels also catch FBIO_WAITFORVSYNC. I'm not sure wether 
other framebuffer drivers handle this in the same way.


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