WebGLTextures: Remove render target texture fallback.

[Mugen87]

Related issue: #8658

Description

Almost six years ago a policy was introduced that disallows the usage of render target as texture.

I think it's okay to remove the respective fallback in WebGLTextures which saves unnecessary function calls and if statements evaluations for each uniforms update.

[gkjohnson]

What happens now if you set a render target as a texture? Does it throw an error or just not render anything? Tbh I still get this wrong some times and the warning is helpful. Would it be possible to just log a warning if the render target is used?

[Mugen87]

I do not vote to do that. The idea is to remove the overhead of such checks. The general policy in the engine is to not evaluate user input for better performance. The current fallback was never intended to be permanent.

[WestLangley]

Is there a compelling reason why WebGLRenderTarget has a texture, rather than extends texture?

[Mugen87]

The design matches the framebuffer/attachments pattern. You can have more than one texture per render target.

[WestLangley]

The design matches the framebuffer/attachments pattern. You can have more than one texture per render target.

You can have more than one THREE.Texture per THREE.WebGLRenderTarget?

[Mugen87]

Yes. For example a render target can have a depth texture attached. And there is MRT.

[mrdoob]

Thanks!