967142 - drawImage and clearRect don't affect the same pixels while scale transform exists

Status: NEW

(Core :: Graphics: Canvas2D, defect)

Description

[Tim Martin]

User Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:29.0) Gecko/20100101 Firefox/29.0 (Beta/Release)
Build ID: 20140131030203

Steps to reproduce:

- Scale the canvas
- draw an image
- clip to a sub rectangle,
- clear that rectangle
- draw the image again.



Actual results:

A line of pixels around the border remains the background color.

Here is a jsfiddle that reproduces the issue: http://jsfiddle.net/VAXrL/1059/
It is somewhat hard to spot in a static image, but there is a clear line of lime green pixels on the TV sprite.


Expected results:

drawImage should draw to every pixel that was cleared.  (This seems to be what Chrome does.)

This is causing a problem in the canvas drawing routine we use in CraftyJS; when a transformation is applied to the canvas, lines of the background color will sometimes appear due to this interaction of clearRect and drawImage.

Comment 1

[Paul Silaghi, QA [:pauly]]

(In reply to Tim Martin from comment #0)
> there is a clear line of lime green pixels on the TV sprite.
Confirmed in FF 29.0a1 (2014-02-03), win 7 x64

Comment 2

[Tim Martin]

Just confirming that I still observe this bug with recent a recent nightly build: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.9; rv:45.0) Gecko/20100101 Firefox/45.0