[Interest] Qt3D Multiple color targets not working

[Paul Lemire]

Hi Gil,

You shouldn't have to actually modify the Material to add in more passes.

What you have to do is edit the fragment shader  to have more than 1
color output:

e.g:

out vec4 fragColor1;

out vec4 fragColor2;

out vec4 fragColor3;

void main() {

fragColor1 = color;

fragColor2 = color;

fragColor3 = color;

}

By default the declaration order of the output maps to your attachments:

first output goes to ColorAttachment0, second output to ColorAttachment1 ...

On 8/6/19 6:14 PM, Gil H wrote:
>
> Thanks Paul.  My understanding of how to accomplish that would be to
> create an Effect with multiple RenderPasses and then in the framegraph
> specify a filter for each pass and the output surface for it.  Is that
> all?  I don’t see anything in the shaders that is specific to the
> attachment… is anything needed on that side of things?
>
>  
>
> Gil
>
>  
>
>  
>
> *From: *Paul Lemire <paul.lemire at kdab.com>
> *Date: *Monday, August 5, 2019 at 2:36 AM
> *To: *Gil H <qt at tastytech.ca>, Qt Interest <interest at qt-project.org>
> *Subject: *Re: [Interest] Qt3D Multiple color targets not working
>
>  
>
> Hi Gil,
>
> I'm pretty sure that's because you are using the PhongMaterial which
> only writes to Depth and Color0. You'd need to have your own material
> which writes to 3 different outputs to properly populate the 3 color
> attachments.
>
> Paul
>
> On 8/1/19 7:42 PM, 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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> -- 
> Paul Lemire | paul.lemire at kdab.com <mailto:paul.lemire 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.fr
> KDAB - The Qt, C++ and OpenGL Experts
>
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-- 
Paul Lemire | paul.lemire 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.fr
KDAB - The Qt, C++ and OpenGL Experts

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