Add PCF25 shadow filtering option in the Compatibility rendering method

[Calinou]

• 4.x version of [3.x] Add PCF25 shadow filtering option in the GLES3 renderer #54355.

This is a high-quality shadow filter which results in smooth, stable shadows even for dynamic objects.

Thanks to early bailing, PCF25 is faster than the old PCF13 implementation while looking better. It's also not that much slower compared to the new PCF13 implementation.

PCF25 is used when the soft shadow quality setting is set to Ultra.

Preview

Hard	Soft Low (PCF5)	Soft High (PCF13)	Soft Ultra (PCF25)

[mrjustaguy]

A question, regarding early bail, doesn't it make sense to sample in the x pattern and not + pattern?

[mrjustaguy]

Eh, Ok Early Bail causes artifacts on 25, even on 13 just not as often...

These Blocks of sudden shadow on PCF25 are caused by Early Bail

I think we should have multiple different versions of this:

1. Hard - No PCF
2. Low - PCF5
3. Medium - PCF13 + early bail
4. High - PCF13 no bail
5. Ultra - PCF25 no bail (no point in providing version with bail if it breaks with any shadows remotely more complex like shown above with the fingers)

[lawnjelly]

Or have early bail as a separate option (e.g. off, medium, high)?

Maybe if we rotated e.g. a disc, the chance of having offensive artifacts from early bail might be reduced.

[mrjustaguy]

Maybe the pattern change from + to x would help, which i asked about earlier..
But yea an on-off option for early bail would be good, however that'd have to be like fully on or off based on how it's working right now.

[Calinou]

These Blocks of sudden shadow on PCF25 are caused by Early Bail

Could you upload a minimal reproduction project? It might be possible to tweak the early bailing pattern to reduce artifacts.

I wouldn't remove early bailing entirely though (or provide an option for what is essentially an optimization), as the performance gain is very significant for something like PCF25. The Compatbility rendering method targets low-end hardware after all, so PCF25 needs to be somewhat usable on mobile and recent integrated graphics.

[mrjustaguy]

I don't have the project where I took this, however the basic creation steps are simple, just get something that has high frequency gaps in shadows, like say an Alpha Hash transparency casting shadows, that just wrecks things worse than the above example.

I'm also afraid that this is just a fundamental flaw of Early Bail, and anything that creates small, pixel or so wide gaps between shadows causes the artifact, and just does so much more easily with PCF25 which is likely why it wasn't noticed and reported before for PCF13, due to a lack of any more complex shadowing scenarios being present for them to show up.
This makes it only suitable to deal with Shadows from buildings, cars and the like that Don't have High Frequency Shadow gaps, and a Nightmare for Trees, Hair, and even just more complex geometry such as humans