599527 - Color Piano not Rendering in Minefield Like in Chrome

Status: UNCONFIRMED

(Core :: Graphics: Canvas2D, defect)

Description

[Chris DeCairos (:cade)]

User-Agent:       Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b7pre) Gecko/20100923 Firefox/4.0b7pre
Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0b7pre) Gecko/20100923 Firefox/4.0b7pre

While testing the performance of Color Piano in Chrome and Firefox, I have noticed that the colored bars that appear below the keys when you play notes leave behind "shadows" after they have faded away. Chrome does not leave these shadows behind.

Reproducible: Always

Steps to Reproduce:
1. Navigate to http://www.chromeexperiments.com/detail/color-piano/
2. When it has finished loading, press any key on the board
3. Watch as the color below the key fades away, it leaves a different shade than the original background.

Comment 1

[Vladimir Vukicevic [:vlad] [:vladv] (needinfo me, slow to respond)]

Looks like a precision/rounding issue.  The color display below is animated by:

1) filling the entire canvas with rgba(0,0,0, 0.05) (that is, 5% black), to fade it to black slightly.
2) drawing the top pixel line with the new colors
3) doing a self-blit, copying (0,0,w,h) -> (0,1,w,h) via drawImage.

(or something like that -- there's additional stuff going on, so that's not precisely correct).  That fill with 5% black is just never actually ending up as true black.  Dunno if it's a real bug or not, you can't really rely on that kind of fill to eventually result in black, given precision limitations.

Comment 2

[Chris DeCairos (:cade)]

Attachment: difference in background colour after pressing piano keys in chrome and fx

This screenshot shows how the fade of colour in chrome returns to black, while in Firefox it does not.

Comment 3

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