[Interest] Qt on direct compose

Giuseppe D'Angelo giuseppe.dangelo at kdab.com
Mon Mar 18 17:26:31 CET 2019


On 18/03/2019 14:32, Pierre Lamot wrote:
> Before starting to perform a draw call, DComposition will inform you where it
> expect you to perform your drawing within the texture it gives you, like an
> OpenGL viewport.  In most cases this will be (0,0) and  will works out of the
> box. Though, especially when dealing with small resolution, DComposition will
> recycle its texture and ask you to draw with a different viewport. I didn't find a
> way to specify the viewport on Qt side, it seems to reset it before drawing the
> scene (probably [4]) .
> So my question is, is there any way I can tell Qt what viewport to use?

Maybe there's a small bit of API missing here on QQuickWindow, to 
specify the viewport that Qt Quick should use when rendering on a FBO? 
(I'd suggest to open a feature request for this, should be relatively 
simple to implement...).

Given the codepath that you pasted, there seems to be no way for a 
custom glViewport in there. And I wouldn't recommend using QSGEngine, 
the effort is definitely not worth it here.

My 2 c,
Giuseppe D'Angelo | giuseppe.dangelo at kdab.com | Senior Software Engineer
KDAB (France) S.A.S., a KDAB Group company
Tel. France +33 (0)4 90 84 08 53, http://www.kdab.com
KDAB - The Qt, C++ and OpenGL Experts

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