Add DepthPass shader

[jjxtra]

Render the depth buffer, useful when you post process only part of the geometry in your application, you can then draw that geometry over the depth buffer from the non-post processed geometry.

[WestLangley]

We generally avoid making gl calls directly because it can mess up the renderer's internal state. You may have to do this:

renderer.state.buffers.color.setMask( ... );

[jjxtra]

Updated

[WestLangley]

It is sort of an awkward API, but it works for you, right?

[jjxtra]

It is working, I will think about a demo, for now it is a contract job that I cannot post anything but the depth pass, which I am using for another personal side project, so happy to share.

[WestLangley]

Would it work to add it to one of the boxes in this example?

[jjxtra]

Could do, the main use case I have found is post processing transparent objects like lines and particles that wrap around, through and behind solid objects.

[WestLangley]

Something cool like that would be ... cool. :-)

[WestLangley]

@mrdoob Why do we have renderer.context exposed, while also having renderer.getContext()?

[WestLangley]

useful when you post process only part of the geometry in your application

I expect there are a lot of users who would appreciate seeing an example of that.

[mrdoob]

@mrdoob Why do we have renderer.context exposed, while also having renderer.getContext()?

I think context was first and then getContext() was added later but kept the first to avoid breaking backwards compatibility. I think it would be okay to remove the former.

[mrdoob]

Agreed that a simple example of the usage would be great. Also to ensure we don't beak it.

[mrdoob]

Do we need an example for this?

[Mugen87]

I don't think this PR is acceptable since a depth pass should not render the scene with the same potentially expensive PBR materials than the beauty pass. AFAIK, doing renderer.context.colorMask(false, false, false, false); does not prevent the fragment shader from being executed.

Besides, I've often encountered situations where I want to sample the depth of the scene in the fragment shader of different object. Check out how the water foam is rendered in this example:

https://codesandbox.io/s/black-mountain-gojcn

Currently, I use this pattern:

scene.overrideMaterial = depthMaterial;

renderer.setRenderTarget(renderTarget);
renderer.render(scene, camera);
renderer.setRenderTarget(null);

scene.overrideMaterial = null;

where renderTarget has a configured DepthTexture if the extension is available. It would be great if a depth pre-pass feature not only renders the depth to achieve the benefits mentioned here #8676 (comment) but also can provide the depth as a render target for further processing.

[Mugen87]

Closing for now. This needs to be implemented differently. #8676 actually looks more promising.