[Bug] - N8AO works incorrectly with adaptiveDpr

Hey everyone! I seems found a bug in N8AO related to AdaptiveDpr

We found a strange effect in our application after adding N8AO to EffectComposer - sometimes it started to add weird 'reflections' to the materials, and we couldn't understand where it's coming from

This is how it looks like: On the surface of the model you can see "reflection" from grid, which should't be present (but it's not only about grid but any objects can appear as reflection).

After debugging for a while I've noticed that this happens on my machine when DPR value is changed. If we (or system) change dpr from 2 to 1, N8AO started to add this 'reflections'. As I can see class has size values which are half of the initial renderer size (if I understand correctly)

If I manually call setSize(width, height) method on N8AOPostPass instance and upscale this values back to dpr=2 values this bug disappears. So it's either should always keep initial values or there is some error in calculation after updating render size

Steps to reproduce
Lest say screen size is 1000x500 with dpr=2. initial values of renderer is 2000x1000px, dpr=2, we set dpr to 1, values are updated to 1000x500, bug appears. If I set values manually by calling setSize() on N8AOPostPass instance to setSize(2x1000, 2x500) it starts working correctly again

versions

"@react-three/drei": "^9.97.5",
"@react-three/fiber": "^8.15.16",
"@react-three/postprocessing": "^2.16.2",
"postprocessing": "^6.35.3",
"three": "^0.161.0",

Can anyone help with this? I can help with fix if you can explain a bit more of how it works. Thanks in advance

Have you ever found a solution to this? I'm facing the same problem.

Hey! Sorry, didn't see your comment

I honestly don't remember how I came up with this solution but it was working, at least with those lib versions

// https://github.com/pmndrs/react-postprocessing/issues/280
const N8AOHacked = () => {
  const [enabled, setEnabled] = useState(true);
  const viewport = useThree((three) => three.viewport);

  useEffect(() => {
    setEnabled(viewport.dpr === viewport.initialDpr);
  }, [viewport]);

  if (!enabled) return null;

  return (
    <N8AO
      color="black"
      aoRadius={1}
      intensity={1}
      aoSamples={5}
      distanceFalloff={0.15}
      denoiseSamples={2}
    />
  );
};

Root cause: <EffectComposer> re-checks its size every frame, but only against gl.getSize(), the CSS size. setDpr / <AdaptiveDpr> change the pixel ratio and leave the CSS size as is, so composer.setSize() never runs. The composer's buffers and every pass (N8AO included) stay at the old drawing-buffer size, so they no longer match the canvas.

Measured in Chromium on a 480×320 canvas after setDpr(2) → setDpr(1): the canvas is 480×320, but the composer and the N8AO pass stay at 960×640. That also keeps post-processing at 3.6× the GPU time the lower ratio should cost (3.03 vs 0.83 ms per frame).

postprocessing's setSize() already sizes everything from getDrawingBufferSize(), so the fix is to include gl.getPixelRatio() in that per-frame check. PR: #381

fix(EffectComposer): resize the composer when the pixel ratio changes

Navigation Menu

Repository navigation

[Bug] - N8AO works incorrectly with adaptiveDpr #280

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

[Bug] - N8AO works incorrectly with adaptiveDpr #280

Description

Activity

goce-cz commented on Jun 25, 2025

AlexanderMoroz commented on Jun 30, 2025

tonyblu331 commented on Sep 25, 2026

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

Issue actions