Implement bicubic sampling for lightmaps

[BlueCube3310]

Supersedes #77912
Closes #49935

Adds support for bicubic sampling in LightmapGI, which results in much smoother-looking baked shadows:

Bilinear	Bicubic

To do:

• Add a project setting for using bicubic sampling,
• Optimize for Mobile & Compatibility,
• Don't break compatibility with older LightmapGIData files.

[fire]

We're unable to approve for merge if the github actions is failing.

https://docs.godotengine.org/en/stable/contributing/workflow/pr_workflow.html

[jcostello]

The bicubic sampling is adding artifacts around the edges of the boxes in the second example?

[BlueCube3310]

The bicubic sampling is adding artifacts around the edges of the boxes in the second example?

Unfortunately yes, this sort of light bleeding happens with low-resolution lightmaps (3 x 256 x 256 for 38 meshes in this case).

[BlueCube3310]

The filtering can now be toggled from the ProjectSettings and the lightmaps are backwards-compatible with older ones, so upgrading should be seamless.

[Calinou]

Tested locally (rebased on top of master 29b3d9e), it works as expected in all rendering methods. Code looks good to me at a glance.

Toggling the project setting works without having to restart the project as well, which is nice for providing graphics options in projects. (This is an upgrade from 3.x where a restart was required when using GLES2, but not GLES3.)

Disabled	Enabled

PS: I noticed toggling bicubic filtering works on existing projects with lightmaps that were baked without this PR. They seem to look fine in this scenario, though I haven't looked extensively to see if they suffer more from lightmap bleeding when bicubic filtering is enabled compared to lightmaps baked with this PR.

Should we print a warning when bicubic filtering is enabled and a LightmapGIData lacks texture size information?

Also, note that this PR prevents using lightmaps baked after this PR is merged from working in older builds not including this PR. The scene will still load but lightmaps won't display until you bake lightmaps again. It's not a dealbreaker, just worth keeping in mind.

[BlueCube3310]

PS: I noticed toggling bicubic filtering works on existing projects with lightmaps that were baked without this PR. They seem to look fine in this scenario, though I haven't looked extensively to see if they suffer more from lightmap bleeding when bicubic filtering is enabled compared to lightmaps baked with this PR.

Should we print a warning when bicubic filtering is enabled and a LightmapGIData lacks texture size information?

If the texture size information isn't present in the file, it's taken from the lightmap textures instead.
The light bleeding is the same, regardless of which version of the file is used. The best way to mitigate it would probably be to increase the padding on the atlas textures in the lightmapper.

[akien-mga]

Suggested change

	ClassDB::bind_method(D_METHOD("lightmaps_set_bicubic_filter", "filter"), &RenderingServer::lightmaps_set_bicubic_filter);
	ClassDB::bind_method(D_METHOD("lightmaps_set_bicubic_filter", "enable"), &RenderingServer::lightmaps_set_bicubic_filter);

To match the docs. Might also be worth changing the C++ methods argument from p_use to p_enable for consistency, but it's not required.

[AThousandShips]

Suggested change

	Adds an object that is considered baked within this [LightmapGIData]. [param texture_size] must match the size of the [i]entire[/i] lightmap texture, which is used for bicubic filtering when rendering the lightmap.
	Adds an object that is considered baked within this [LightmapGIData]. [param texture_size] must match the size of the [i]entire[/i] lightmap texture which is used for bicubic filtering when rendering the lightmap.

No break here in English I'd say

[AThousandShips]

You will also need to add compatibility binds