From a00a76e7ed25f3e6576d7fced9e0ae317a9ca9da Mon Sep 17 00:00:00 2001 From: tylerjenningsw Date: Tue, 13 Oct 2026 20:45:20 -0400 Subject: [PATCH] Particles: a birth schedule from a rate per step (#1373) psim::births_at builds the GPU's birth schedule (the birth step of every particle id) from the rate of each step, with the CPU step's carry arithmetic. births() for a constant rate now uses it. It stops as soon as the cap would be passed, before adding a step's births, so a huge rate can't build a huge list first. --- crates/effects/src/psim.rs | 18 ++++++++++++------ 1 file changed, 12 insertions(+), 6 deletions(-) diff --git a/crates/effects/src/psim.rs b/crates/effects/src/psim.rs index aabbcdce8..5716a2dcb 100644 --- a/crates/effects/src/psim.rs +++ b/crates/effects/src/psim.rs @@ -85,21 +85,27 @@ pub trait ParticleSim: Send + Sync { /// (the CPU step's `carry` arithmetic, exactly). `None` when more than `cap` would be born (the /// CPU drops births at its live-particle cap, which an independent simulation can't know). pub fn births(rate: f64, steps: u64, cap: usize) -> Option> { - let per = rate / SPS; - if per * steps as f64 > cap as f64 + 2.0 { + if rate / SPS * steps as f64 > cap as f64 + 2.0 { return None; } + births_at(steps, cap, |_| rate) +} + +/// [`births`] with the rate of each step, `rate(i)` particles per second during step `i` (a +/// keyframed Birth Rate, #1373). +pub fn births_at(steps: u64, cap: usize, rate: impl Fn(u64) -> f64) -> Option> { let mut out = Vec::new(); let mut carry = 0.0f64; for i in 0..steps { - carry += per; + carry += rate(i) / SPS; let n = carry.floor() as u32; carry -= n as f64; - for _ in 0..n { - out.push(i as u32); + if n as usize > cap.saturating_sub(out.len()) { + return None; } + out.extend(std::iter::repeat_n(i as u32, n as usize)); } - (out.len() <= cap).then_some(out) + Some(out) } /// Steps per second of the stepped simulations.