Fix: Unity Shader Variant Collection Not Warming Up

A game still hitches the first time each effect appears, even though a ShaderVariantCollection asset exists and WarmUp is called. The collection doesn’t contain the right variants.

Record Real Variants

Edit → Project Settings → Graphics → “Save to asset” under Shader Loading. Play through the game touching every effect, then save. This captures the actual variants used — guessing keyword combinations by hand always misses some.

Call WarmUp at the Right Time

[SerializeField] ShaderVariantCollection variants;

IEnumerator PreloadShaders()
{
    variants.WarmUp();   // blocks; do it behind a loading screen
    yield return null;
}

WarmUp compiles/uploads the variants synchronously — it’s a hitch itself. Hide it behind a loading screen, not mid-gameplay.

WarmUpProgressively

For large collections, WarmUpProgressively(count) spreads compilation across frames so the loading screen stays responsive.

Keep It Current

Add a new effect or shader keyword and the collection is out of date again. Re-record before each release, or automate variant collection in CI by running a playthrough.

Verifying

After WarmUp, trigger each effect for the first time — no compilation hitch. The Frame Debugger shows no “Create GPU Program” spikes during gameplay.

“Warm-up only helps if the collection holds the real variants. Record from a playthrough, warm up behind a loading screen.”

On consoles, shader hitches are a cert risk — treat the variant collection as a release artifact you regenerate every build.