Reduce threshold for discarding small splats

[javagl]

Description

Reduces the threshold for a discard in the splat renderer from 2x2 pixels to ~0.7x0.7 pixels.

Issue number and link

#13304

Testing plan

A test data set with a sandcastle:

splatsDiscard.zip

Here is a comparison of rendering that splat data set with JSplat and with CesiumJS:

That moiré effect for CesiumJS is certainly not desired. It's not clear whether this is "related" to this change, because with that early discard, the splats simply disappeared before it could happen. But maybe that can be tracked in a dedicated issue.

Author checklist

• I have submitted a Contributor License Agreement
• I have added my name to CONTRIBUTORS.md
• n/a? I have updated CHANGES.md with a short summary of my change
• n/a I have added or updated unit tests to ensure consistent code coverage
• I have updated the inline documentation, and included code examples where relevant
• I have performed a self-review of my code

AI acknowledgment

• I used AI to generate content in this PR
• If yes, I have reviewed the AI-generated content before submitting

[github-actions]

Thank you for the pull request, @javagl!

✅ We can confirm we have a CLA on file for you.