[Interest] Qt3D Multiple color targets not working

Sean Harmer sh at theharmers.co.uk
Wed Aug 7 10:40:28 CEST 2019

Hi Gil,

With an FBO with multiple textures attached each texture will still have 
the same pixels rasterised. You can't draw different cameras and scenes 
into each texture at the same time. Well something like that can be done 
with some advanced use of the geometry shader but I don't think that's 
the case here.

If you want to draw 3 different scenes into 3 different textures you 
will need 3 different sub-trees in your framegraph. Each one will set 
the camera to use, the filters to select the subset of the scene graph 
to draw and the FBO with the target texture to render into.



On 01/08/2019 18:42, Gil H wrote:
> Hello everyone, I’m sure I’m doing something wrong here, but 
> basically, I’m trying to render multiple frame graph subtrees into 
> multiple texture targets, and then draw those as part of the final 
> scene (kind of like seeing security camera feeds on a few textured 
> quads).  Attached is my minimal test app which shows that only 
> textures attached to Color0 seem to contain anything.  Is it because 
> the surface is a QWindow?  I’ve tried a more complicated example with 
> an offscreen render surface and an FBO with multiple color attachments 
> added to it, but the textures I got back from that were still empty.
> Tested this on Mac with Qt 5.13.0.
> If anyone is curious about why you would want to do this, I need to 
> render up to 3 different Qt3D scenes for integration into an external 
> GL engine.  So different camera views and scene sub-trees need to be 
> drawn onto separate textures each frame.
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