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Alpha pass costs 2.3-2.9 ms #4

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opened 2026-09-27 03:40:57 +00:00 by sky_line · 2 comments

sky_line commented

2026-09-27 03:40:57 +00:00

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pass2 (alpha-blend + particles) is now the largest single GPU item after the depth pre-pass. Profile what's in it (overdraw of blended geometry, particles, per-pixel lighting on alpha) and reduce.

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2026-09-27 03:40:57 +00:00

sky_line referenced this issue

2026-10-04 14:09:14 +00:00

LL perf (Textures/assets): Texture cache I/O pattern and LRU #300

sky_line referenced this issue

2026-10-05 16:50:14 +00:00

Investigate: local (private) chat translation + grammar help -- CPU translation models, LanguageTool, bring-your-own endpoint #440

sky_line added this to the Slipstream project

2026-10-06 15:04:14 +00:00

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2026-10-10 05:05:04 +00:00

sky_line commented

2026-10-10 05:33:02 +00:00

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No work specific to this ticket found in the history (no commits referencing it; the alpha pass has only benefited indirectly from general perf work such as 1a97085c77). Moving from Testing to To Do until the alpha pass is profiled and reduced.

No work specific to this ticket found in the history (no commits referencing it; the alpha pass has only benefited indirectly from general perf work such as 1a97085c77). Moving from Testing to To Do until the alpha pass is profiled and reduced.

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2026-10-10 05:33:03 +00:00

sky_line commented

2026-10-10 09:17:10 +00:00

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Closing: the measurements no longer support this ticket.

Re-measured 2026-10-10 (RTX 5090, 3840x2088 with FSR, ~62 avatars, sim fully loaded, particles on), averaged over six GPU timer samples:

Pass 2 part	ms/frame
Alpha after water (static)	0.75
Alpha before water (static)	0.29
Rigged alpha after water (~3.0M tris)	0.29
Alpha depth + sort + refraction exclusion	~0.32
Particles	~0.45
Total	~2.1

Blended-geometry fragment work is well under one invocation per pixel, so overdraw is no longer the issue. Particles were the real cost and are fixed by #435 (29.3 ms -> ~0.6 ms in a heavy scene). Pass 2 is no longer the largest GPU item: probe tracing, pre-skinning and the RT build/refit each cost as much or more.

Rigged alpha in crowds stays tracked in #260.

Closing: the measurements no longer support this ticket. Re-measured 2026-10-10 (RTX 5090, 3840x2088 with FSR, ~62 avatars, sim fully loaded, particles on), averaged over six GPU timer samples: | Pass 2 part | ms/frame | |---|---| | Alpha after water (static) | 0.75 | | Alpha before water (static) | 0.29 | | Rigged alpha after water (~3.0M tris) | 0.29 | | Alpha depth + sort + refraction exclusion | ~0.32 | | Particles | ~0.45 | | **Total** | **~2.1** | Blended-geometry fragment work is well under one invocation per pixel, so overdraw is no longer the issue. Particles were the real cost and are fixed by #435 (29.3 ms -> ~0.6 ms in a heavy scene). Pass 2 is no longer the largest GPU item: probe tracing, pre-skinning and the RT build/refit each cost as much or more. Rigged alpha in crowds stays tracked in #260.

sky_line

2026-10-10 09:17:10 +00:00

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