DepthTexture: change default type to UnsignedIntType

[wmcmurray]

Description

I noticed depth precision issues (horizontal banding + z-fighting) when rendering my project with post-processing (using WebGLRenderTargets) starting at very short distances (10 - 15 meters, where 1 unit = 1 meter), and those issues did not happen when rendering the same scene directly to canvas !

So I investigated, and it turns out setting a DepthTexture with the UnsignedIntType type into renderTarget.depthTexture fixed my issues. Precision issues only appear at much greater distances now (as expected) and exactly where they start appearing when rendering directly to canvas.

About this PR

So I changed the default to UnsignedIntType because I believe defaults should give best results out of the box, but I don't know what I'm doing, I didn't test anything beyond my project, and I don't know the implications of this change ⚠️
(also updated the docs + bits of code that seemed relevant)

This example: https://threejs.org/examples/webgl_depth_texture.html helped me to visualize different types, just zoom out until the meshes are barely visible and you should notice banding with UnsignedShortType.

[Mugen87]

I think we have decided to use UnsignedShortType in the past since it is the most performant option and the related depth precision might be sufficient for certain scenarios.

That said I've noticed on more than one occasion that users run into the same issue like you but can't find a solution by themselves. Using UnsignedIntType as the default should mitigate this situtation.

However, if we want to head for quality, using DepthStencilFormat and UnsignedInt248Type is even the better default. Only this setup guarantees at least 24 bit depth precision which is more than UnsignedIntType. And unlike floating point textures it should be supported on all platforms.

[mrdoob]

@wmcmurray Could you give DepthStencilFormat and UnsignedInt248Type a try?

[wmcmurray]

@mrdoob Both DepthFormat + UnsignedIntType and DepthStencilFormat + UnsignedInt248Type resulted in seemingly identical results. I haven't noticed any performance drop either, when I enable post-processing I get an increase of 0.5 - 1 ms per frame in both cases (which is exactly what I get using UnsignedShortType also).

[Mugen87]

The difference in depth precision varies from device to device. So yes, it is possible that you don't see a difference between UnsignedIntType and UnsignedInt248Type. However, guaranteed precision with UnsignedInt248Type is definitely higher.

[mrdoob]

Lets use UnsignedInt248Type by default then?

[Mugen87]

Reconsidering this issue: WebGLRenderTarget.stencilBuffer is false by default which is also an appropriate default. However, I'm not entirely sure if it's safe to use DepthStencilFormat with a render target that has no stencil attachment. I can' tell from the WEBGL_depth_texture spec if this combination is supported on all platforms.

Hence, I think the PR is fine as it is.

[mrdoob]

Thanks!