278475 - GIF image with transparent background flickers

Status: RESOLVED INVALID

(Core :: Graphics: ImageLib, defect)

Description

[Boris Zbarsky [:bzbarsky]]

Attachment coming up.  The gif in question has a background that looks like it
should be transparent (in GIMP), but flickers between transparent and black as
the image animates...

Originally reported on Windows, and I'm seeing it on Linux with current trunk
builds.

Comment 1

[Boris Zbarsky [:bzbarsky]]

Attachment: The image in question

Comment 2

[tor]

This gif is constructed with only one graphics control extension which
specifies the timing and the transparent index.  It appears whatever
app generated the image expected the control extension to apply to the
three subsequent images.  The gif specification states that the scope
of the extension is the graphics rendering block that follows it.  Per
spec we clear the extension state at the end of sub block, so only one
frame will show with the transparent background.

Leaving open for paper to give a second opinion, but it looks like our
behavior is correct.

Comment 3

[ArronM (:paper)]

tor is correct, resolving to INVALID

Transparency (and any other control block properties) only apply to the frame
it's specified on and does not carry over to future frames.
Only the first frame contains a control block, the remaining frames do not, so
they don't have a transparency.