GUI late render pass

[valleymouth]

Hi Robert,
What would be the best way to implement a GUI late render pass? What I want is to render my 3D scene first and then have a GUI render pass using the same framebuffer, but with depth test disabled, so everything would render on top of the current view. I would still need to place certain GUI elements on top of 3D nodes, so I would need to access their transforms, and maybe a need a Switch? Would I need a separate RenderGraph for that? Just need your brain to point to the right direction on how you would implement this.
Cheers,
Denis

[robertosfield]

Hi Denis,

If you want to render text ontop of 3d elements in the scene and have them track the objects what I would do is put the text into the scene graph the underneath the transform that moves the object and set it's layout to billboard so it remains axis aligned and is able to scale nicely. The text position you'd set in the local coordinate frame of that subgraph.

Now the trick to making sure it renders would be to set the text depth value to 1.0 so that it always draws on top, to do this you'll need to override the Text graphics pipeline set by assigning a custom ShaderSet to the vsg::Text element. The vsgtext example has a code path that illustrates how to customize the ShaderSet to disable the depth test, this doesn't do exactly what I'm thinking of but gets you along some of the way.

In a project that uses VSG I've been using this approach to render text at infinity by assigning my own vertex shader assigned a modification of the standard one passed back from vsg::createTextShaderSet(..) which is another approach you could take.

I would suggest trying this approach over trying to have a separate subgraph for overlays as it would avoid the complexity of trying to keep the positions and other scene graph state that affects both the 3d model and the text in sync.