Texture2DRD Global RenderingDevice Documentation

[Akeal]

Updated documentation to specify that Texture2DRD is only supported by the global rendering device.

Example:

In ...
texture_rd.cpp
_set_texture_rd_rid()

ERR_FAIL_COND(!RD::get_singleton()->texture_is_valid(p_texture_rd_rid));

This fail condition ensures that the rendering device global singleton owns the RID that is being assigned to the Texture2DRD, and errors if it is owned by another rendering device (is designated as not valid).

There are many other instances in texture_rd.cpp that call RD::get_singleton() as well.

[Calinou]

Is this intended behavior of Texture2DRD? If it's a bug, it should be reported in its own issue.

Also, does this apply to other *RD classes?

cc @clayjohn @BastiaanOlij

[BastiaanOlij]

@Calinou that's actually a really good question.

Yes in theory you could create TextureRD textures for a texture id created on a local rendering device instance BUT you wouldn't be able to actually use it.

TextureRD was added so we can wrap custom texture objects in a Texture object that can be used on materials. Those don't work across rendering devices (at this point in time), so there would never be a valid use case where TextureRD can be used outside of the global rendering device, hence the code assuming we're only dealing with texture id's created on the global rendering device and erroring out if you give it any other texture id.

That said, there have often been requests to make it possible to populate texture data on a local rendering device in a separate thread, where the end result is then used by the main renderer. However that would likely require either a transfer of the end result between contexts, or creating a shared texture object on the global rendering device and the TextureRD being related to the global rendering device texture id of this shared texture. Hard to say though until we actually have support for this (if we ever get there).

So my gut feeling is that at this point in time, the ERR_FAIL_COND should be in place on all these functions, and specifically naming the global rendering device in the documentation is probably a good idea.

[Mickeon]

So what should be done in this PR? Do you think it's a good idea as is?

I would recommend changing the commit and the title of this PR to be somewhat more descriptive.