Particles blurry / pixelated at distance (possibly only alpha-blended ones) #879

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opened 2026-10-19 20:18:08 +00:00 by sky_line · 1 comment

sky_line commented

2026-10-19 20:18:08 +00:00

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Particles look blurry / pixelated at distance. Possibly only alpha-blended particles (to confirm: compare additive / glow sprites with alpha ones).

Suspects (in order)

Reduced-resolution particle pass (RenderVKParticleLowRes, default 2 = adaptive; RenderVKParticleResScale):
- Blend-pair sprites (alpha, additive, premultiplied) are drawn into an offscreen target at a lower resolution, then composited with a nearest-depth upsample.
- Distant particles are small on screen, so a half- or quarter-res target turns them into a few blocky texels. Nearest-depth upsampling against a downsampled depth can also pick the wrong texel at silhouettes.
- This would also explain "only alpha ones": those are the blend pairs routed into the low-res target.
Texture mip / residency for particle textures. Distance-based mip requests or residency (texture budget / pressure bias) can load a low mip, and BC compression can blur a small sprite texture. Check debug views 23 and 24 on a particle texture.
Alpha-coverage / alpha mips (#766 kept alpha-coverage mips separate from blended uses). Check that particle textures take the blended-mip path with correct filtering.
TAA / FSR reactive mask on composited particles: a low-res reactive mask smearing small, distant sprites.
VRS on alpha, if particles are drawn under a coarse shading rate.

Steps

A/B on the same distant emitter:
- RenderVKParticleLowRes 0 vs 2;
- RenderVKParticleResScale;
- TAA / FSR off;
- texture compression off;
- VRS off.
Screenshot each. Also compare with LL's viewer for the look of the same emitter.
If the low-res pass is the cause: make the adaptive mode keep small / distant sprites at full resolution (route by projected sprite size), or use a better upsample (bilateral / edge-aware instead of nearest).

Acceptance

Distant particles, alpha and additive, look as sharp as the full-resolution path. The low-res pass still pays off where particles cover a lot of the screen (smoke, fog sprites).

Particles look **blurry / pixelated at distance**. Possibly only alpha-blended particles (to confirm: compare additive / glow sprites with alpha ones). ## Suspects (in order) 1. **Reduced-resolution particle pass** (`RenderVKParticleLowRes`, default 2 = adaptive; `RenderVKParticleResScale`): - Blend-pair sprites (alpha, additive, premultiplied) are drawn into an offscreen target at a lower resolution, then composited with a nearest-depth upsample. - Distant particles are small on screen, so a half- or quarter-res target turns them into a few blocky texels. Nearest-depth upsampling against a downsampled depth can also pick the wrong texel at silhouettes. - This would also explain "only alpha ones": those are the blend pairs routed into the low-res target. 2. **Texture mip / residency for particle textures.** Distance-based mip requests or residency (texture budget / pressure bias) can load a low mip, and BC compression can blur a small sprite texture. Check debug views 23 and 24 on a particle texture. 3. **Alpha-coverage / alpha mips** (#766 kept alpha-coverage mips separate from blended uses). Check that particle textures take the blended-mip path with correct filtering. 4. **TAA / FSR reactive mask** on composited particles: a low-res reactive mask smearing small, distant sprites. 5. **VRS on alpha**, if particles are drawn under a coarse shading rate. ## Steps - A/B on the same distant emitter: - `RenderVKParticleLowRes 0` vs 2; - `RenderVKParticleResScale`; - TAA / FSR off; - texture compression off; - VRS off. - Screenshot each. Also compare with LL's viewer for the look of the same emitter. - If the low-res pass is the cause: make the adaptive mode keep small / distant sprites at full resolution (route by projected sprite size), or use a better upsample (bilateral / edge-aware instead of nearest). ## Acceptance Distant particles, alpha and additive, look as sharp as the full-resolution path. The low-res pass still pays off where particles cover a lot of the screen (smoke, fog sprites).

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2026-10-19 20:18:08 +00:00

sky_line added this to the Slipstream project

2026-10-19 20:18:08 +00:00

sky_line referenced this issue from a commit

2026-10-22 08:20:13 +00:00

#879: particles stay sharp at distance -- size routing + edge-aware low-res upsample

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