Using vsg::DepthSorted to display nodes always on top of others

[Vic-Min]

I need some nodes to be displayed always on top of others.
In OSG I achieved this by placing nodes in different bins.
I wanted to do the same in VSG using vsg::DepthSorted.
But it didn't work for me. The nodes go into different bins, but it doesn't cause the node from the bin with the higher number to be on top of the node from the bin with the lower number.
What am I doing wrong?

Here is a minimal, reproducible example with two colored squares in different bins and the resulting scene.
Depending on the viewpoint, one or the other square is drawn at the top.

[AnyOldName3]

I think you want vsg::Layer combined with disabled depth testing. vsg::DepthSorted means that the draw order is controlled by an object's depth, and also does one of the things vsg::Layer does (i.e. put things in a later bin), but it only sounds like you need the part vsg::Layer does. As well as that, it sounds like you need to disable depth testing for these objects so they stop caring that the depth buffer says there's something in front of them.

[Vic-Min]

Yes, I have tried using vsg::Layer. It works.
But, I have hundreds of nodes that need to be drawn on top of other nodes. And I can't put them in one vsg::Layer. Each one will be in its own vsg::Layer. And when using vsg::Layer, I need to add vsg::ClearAttachments before each node. Won't there be performance issues when using hundreds, maybe thousands, of vsg::ClearAttachments?

Still, going back to the original question, I would like to understand: am I using vsg::DepthSorted incorrectly or is it a VSG bug? After all, the nodes are placed in different bins, just like when using vsg::Layer, but it doesn't cause the node from the bin with the higher number to be displayed on top of the node from the bin with the lower number.

[robertosfield]

Children of a Layer will be record in order the children traversed in, so you should be able to just add them in the order you want them rendered. If you disable depth write or depth test then all the fragments in the later rendered meshes will appear on top.

So, it should be possible to use a single vsg::Layer.

[Vic-Min]

I achieved the desired behaviour using vsg::DepthSorted by disabling the depth test for nodes placed in bins with large numbers.
Here is the modified minimal example and the resulting scene. Maybe someone will find it useful.

But the resulting code of disabling depth testing for nodes created by vsg::Builder looks ugly in my opinion:

auto quad = builder->createQuad(geomInfo, stateInfo);
if (auto& stateGroup = quad.cast<vsg::StateGroup>())
	for (auto& stateCommand : stateGroup->stateCommands)
		if (auto& graphicsPipeline = stateCommand.cast<vsg::BindGraphicsPipeline>())
			if (auto& pipeline = graphicsPipeline->pipeline)
				for (auto& pipelineState : pipeline->pipelineStates)
					if (auto& depthStencilState = pipelineState.cast<vsg::DepthStencilState>())
						depthStencilState->depthTestEnable = VK_FALSE;

Also, I see vsg::BindGraphicsPipeline duplication at the nodes in the scene. Can this be done in a more elegant way?

[robertosfield]

You can set the state defaults for the vsg::Builder to use by customizing the a ShaderSet and assigning it to the vsg::Builder, this should be simpler than post processing. The same approach can be used when providing custom ShaderSet to loaders via vsg::Options::shaderSets[].

Creating lots of separate bins doesn't sounds efficient, a single Bin but controlling the draw order would be better way of managing the scene. It might be that vsg::Layer is the right tool, but without more background I can't say for sure.

You haven't actually explained what you result you are trying to achieve, instead have gone directly to how you are trying to achieve something. It's often best to first explain what you are trying to achieve first at a high level, then what you have tried and show the issues you have. Screenshots are helpful in explaining what you are tyring to achieve as well as the results.

With this type of extra background information it's much easier for us to point you in the right direction.