Fix PMREM banding on Pixel

[elalish]

Fixes #18265

The issue is that floor( x / pixelRatio * pixelRatio ) != x when pixelRatio is non-integer, due to floating point error. By adding half a pixel, we ensure floor always goes the right way.

[elalish]

The other option would be to change this line https://github.com/mrdoob/three.js/blob/dev/src/renderers/WebGLRenderer.js#L467 from floor to round, but I'm guessing there are reasons it is the way it is.

[sciecode]

Confirmed solved on my end. Thank you.

Dev Example
Branch Example - updated build*

[Mugen87]

@sciecode I'm afraid the live link does not make sense since the build files are not updated yet.

[sciecode]

@sciecode I'm afraid the live links do work since the build files are not updated yet.

Forgot PMREMGenerator is part of source, thank you.
Will update link with a custom branch with updated build.

Edit: done.

[WestLangley]

The other option would be to change this line https://github.com/mrdoob/three.js/blob/dev/src/renderers/WebGLRenderer.js#L467 from floor to round, but I'm guessing there are reasons it is the way it is.

#16821 explains the change. I do not recall if I considered round().

[Mugen87]

Yes, the banding is now gone on my Pixel 1 👍

[Mugen87]

Merging this and updating dev for more testing.

[Mugen87]

72018fa

[mrdoob]

Thanks!