Add anisotropic filtering to GLES2 backend

[furrykef]

Fixes #45641

I made this change by copying the relevant code from the GLES3 backend to the GLES2 backend. In so doing, I noticed a strange line, line 8358 of rasterizer_storage_gles3.cpp:

config.use_anisotropic_filter = config.extensions.has("rendering/quality/filters/anisotropic_filter_level");

The strange thing about it is, as far as I can tell, this variable soon gets overwritten without having been used. Still, I copied this line even though I'm not sure it has any effect.

(EDIT: I have discussed this line with other devs and removed it from the GLES2 backend. It's still in the GLES3 backend, though.)

(EDIT: It's gone from both backends now.)

[lawnjelly]

Looks fine to me although I haven't tested. Great first PR. 👍

Seeing the duplication in texture_set_data and texture_set_flags reminded me I noticed a lot of code duplication here when converting this for Godot 4.0. In there I used a separate function to do all the common stuff between the two functions. It should be fine to leave like this though in 3.2.

[akien-mga]

Looks good to me! I'll let @clayjohn do the final review.

As a tip for future PRs, you might want to make them from a dedicated branch instead of your 3.2 branch, so that you can easily create new branches for new PRs even before the first one is merged.

[Calinou]

I'd like to do some testing on Android and HTML5 before this is merged, just in case 🙂

Edit: I tested this PR and it works successfully on Linux (NVIDIA), HTML5 (Linux + Firefox, Linux + Chromium, Android + Chromium) and Android (OnePlus 6).

Minimal reproduction project: test_anisotropic_gles2.zip (includes Android and HTML5 exports)

In the above project, an isotropic texture is displayed on the left, an anisotropic texture is displayed on the right with 16× anisotropic filtering.

Screenshots

Linux (NVIDIA)

HTML5 (Linux + Firefox)

HTML5 (Linux + Chromium)

HTML5 (Android + Chromium)

Android (OnePlus 6)

[clayjohn]

Great work!

[akien-mga]

Thanks! And congrats for your first merged Godot contribution 🎉