[RENDERDRAGON] particles_blend material is now culled

Partner Rank:

3

Partner Team Reporting:

Everbloom Games

Verification builds:

All Render Dragon versions (e.g. 1.16.200.01_rc0 renderdragon)

Summary:

The particles_blend particle material now culls back faces, making them invisible if seen from behind. This is particularly evident when using directional, non-billboard particles.

Impact:

We typically use non-directional particles for things like logos and graphics, and don't pay much attention to their orientation in the world because they used to be two-sided. One instance of this effect is in the bands at the end of levels.  They are supposed to be visible from both sides, but they're only visible if you're already past it.

Repro Steps:

1. Open the provided world
2. Head to the magenta-floored chunk
3. Look at the gradient particles above the repeating command blocks

Expected:

All four sides should be visible at all times

Observed:

Only the front two sides facing the player are visible at any one time

Screenshots/Videos attached: Yes/No

Yes

Regression Builds:

Last worked in all DX11 versions

Notes:

On a slightly related note, I have defined a custom `particles_blend_one_sided` particle via a particles.material, which extends particles_blend and "-states": ["DisableCulling"], in order to achieve the effect that the particles have now (used in Be a Dragon and another upcoming map). Weirdly enough, those particles no longer work, and instead look exactly like particles_alpha does. I'm not sure if this bug is the cause, or if custom materials no longer work. In either case, a native one-sided particle material would be appreciated, as defining custom materials and having them potentially break is often a source of anxiety.