Add high quality glow mode (3.x)

[Calinou]

This backports the high quality glow mode from the master branch. Thanks @clayjohn for the original implementation 🙂

Previously, during downsample, every second row was ignored. Now, when high-quality is used, we sample two rows at once to ensure that no pixel is missed. It is slower, but looks much better and has a much high stability while moving.

High quality also takes an additional horizontal sample the width of the horizontal blur matches the height of the vertical blur.

This closes #43110.

Preview

GLES3

Low quality (default)	High quality

GLES2 (Bloom = 1, since there is no HDR)

Low quality (default)	High quality

[clayjohn]

Fracteed requested this. It is not a risky change and is opt-in so @akien-mga if you are comfortable we could merge this for 3.4

[akien-mga]

Thanks!

[RichardR01]

I hardly notice the difference between low and high, except that high quality seems to blend better. Also it would be nice if we had a tagging system where the glow only effects certain objects. You wouldn't even need a new identifier, you can use the already existing grouping functions. So like if I add "glow" to the group for specific objects, then only those objects would be affected by the post process effect. Even if it can't work exactly like that, an identifier of some sort would be great. (This has been asked before).

[Calinou]

I hardly notice the difference between low and high, except that high quality seems to blend better. Also it would be nice if we had a tagging system where the glow only effects certain objects. You wouldn't even need a new identifier, you can use the already existing grouping functions. So like if I add "glow" to the group for specific objects, then only those objects would be affected by the post process effect. Even if it can't work exactly like that, an identifier of some sort would be great. (This has been asked before).

When using GLES3, this can already be done by increasing the glow effect's HDR Threshold property and making your "glowy" objects brighter. Surfaces darker than the HDR threshold won't generate any glow.

If you need further control for artistic reasons, using glow billboard sprites is a reasonable (and often cheaper) alternative. This way, you can do pretty much anything: use different shapes, colors, etc. Use SpatialMaterial's Proximity Fade and Distance Fade properties to your advantage here.