1515237 - ClientTiledPaintedLayer::InvalidateRegion is slow on Android (because of low precision rendering)

Status: RESOLVED WONTFIX

(Core :: Graphics: Layers, enhancement, P3)

Description

[Markus Stange [:mstange]]

Profile: https://perfht.ml/2R2vLv4

In bug 1368386 I optimized ClientTiledPaintedLayer invalidation so that on platforms without low precision rendering, mInvalidRegion.GetRegion() would only  be called once per paint. But we use low precision rendering on Android, so Android is currently missing that optimization:

https://searchfox.org/mozilla-central/rev/13788edbabb04d004e4a1ceff41d4de68a8320a2/gfx/layers/client/ClientTiledPaintedLayer.h#60-61
>  virtual void InvalidateRegion(const nsIntRegion& aRegion) override {
>    mInvalidRegion.Add(aRegion);
>    UpdateValidRegionAfterInvalidRegionChanged();
>    if (!mLowPrecisionValidRegion.IsEmpty()) {
>      // Also update mLowPrecisionValidRegion. Unfortunately we call
>      // mInvalidRegion.GetRegion() here, which is expensive.
>      mLowPrecisionValidRegion.SubOut(mInvalidRegion.GetRegion());
>    }
>  }

The profile above was captured on dailymail.co.uk (bug 1511731), and it demonstrates that this slow path is an actual performance problem. We shouldn't spend 1.5 seconds in a single paint on updating regions.

Comment 1

[Darkspirit]

bug 1727398