A fillStyle bug on Chrome canvas

[Akira Kuroiwa]

Hi, I found a fillStyle bug on Chrome canvas. 

When assigning "rgba(255, 0, 0, 0.5)" to ctx.fillStyle (ctx is a context of a canvas here) on Chrome for PC, the value is automatically changed to "rgba(255, 0, 0, 0.501960784313726)", where the other browsers (Firefox, Safari, Chrome) are "rgba(255, 0, 0, 0.5)". 

Please see a PoC below for details.

I think the alpha value 0.501960784313726 is basically came from 128 / 255, however, the detail is unknown. (It may be related to some decimal rounding problem, because the changed value takes discrete values when we give 0.005883 and 0.05882999999999)

PoC:

https://codepen.io/kakira/pen/PoORpQO

Environments:

- Windows:

  - Chrome 98.0.4758.102 -> incorrect value

  - Firefox 97.0.1 -> correct value

  - Edge 98.0.1108.56 -> incorrect value

- Mac:

  - Chrome 98.0.4758.102 -> incorrect value

  - Firefox 96.0.3  -> correct value
  - Safari 17612.3.6.1.6  -> correct value

- Android:

  - Chrome 98.0.4758.101 -> incorrect value

- iOS:

  - Chrome 98.0.4758.97 -> correct value

PoC result images:

0.00582999999999 vs. 0.00583:

thanks!

[Lei Zhang]

Please use Chromium's bug tracker to report bugs. https://new.crbug.com/

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[Akira Kuroiwa]

Thank you, and I reported the isuue on bug tracker.

https://bugs.chromium.org/p/chromium/issues/detail?id=1300389

2022年2月23日水曜日 15:51:09 UTC+9 Lei Zhang: