WebGLBackend: `copyTextureToTexture` doesn't copy all layers of 3D render targets

[shotamatsuda]

Description

In WebGL fallback, copyTextureToTexture doesn't copy all layers of 3D render target textures.

I noticed the implementation of copyTextureToTexture in WebGLBackend deviates from the one in WebGLRenderer. I can make a PR if those can be made the same (there are a couple of differences in the conditionals which I don't fully understand).

Reproduction steps

1. Copy a 3D render target texture to another 3D render target texture using copyTextureToTexture in WebGL fallback.

Code

const rt1 = new RenderTarget3D(size, size, size)
// Draw the contents of "rt1"

const rt2 = new RenderTarget3D(size, size, size)
renderer.setRenderTarget(rt2)
void renderer.clear()
renderer.setRenderTarget(null)

renderer.copyTextureToTexture(
  rt1.texture,
  rt2.texture,
  new Box3(new Vector3(), new Vector3().setScalar(size))
)

Live example

https://jsfiddle.net/shotamatsuda/xu8zs0g2/

Screenshots

Version

r179

Device

Desktop

Browser

Chrome

OS

MacOS

[Mugen87]

I can make a PR if those can be made the same (there are a couple of differences in the conditionals which I don't fully understand)

That would be great! It's a unfortunate when WebGLRenderer is updated without honoring the WebGL backend in WebGPURenderer. Ideally, PRs keep them in sync if possible.