1511290 - GIF animation frame delay used for multiple frame instead of next block only

Status: RESOLVED FIXED

(Core :: Graphics: ImageLib, defect, P3)

Description

[Robert Ancell]

Attachment: animation-multi-image.gif

User Agent: Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:63.0) Gecko/20100101 Firefox/63.0

Steps to reproduce:

I have generated a GIF image (attached) that contain the following data:

Version: b'GIF89a'
Size: 2x2 pixels
Original Depth: 8 bits
Colors (4): #000000, #ffffff, #ff0000, #00ff00
Background Color: #000000 (0)
Netscape Extension:
  Loop Count: 0
Graphic Control Extension:
  Delay Time: 50/100 ms
  Disposal Method: keep
  User Input: False
Image:
  Size: 2x2
  Pixels (4, code-size=3): [1, 0, 0, 0]
Image:
  Position: 1,0
  Size: 1x1
  Pixels (1, code-size=3): [2]
Graphic Control Extension:
  Delay Time: 50/100 ms
  Disposal Method: keep
  User Input: False
Image:
  Position: 1,0
  Size: 1x1
  Pixels (1, code-size=3): [1]
Image:
  Position: 1,1
  Size: 1x1
  Pixels (1, code-size=3): [2]
Graphic Control Extension:
  Delay Time: 50/100 ms
  Disposal Method: keep
  User Input: False
Image:
  Position: 1,1
  Size: 1x1
  Pixels (1, code-size=3): [1]
Image:
  Position: 0,1
  Size: 1x1
  Pixels (1, code-size=3): [2]
Graphic Control Extension:
  Delay Time: 50/100 ms
  Disposal Method: keep
  User Input: False
Image:
  Position: 0,1
  Size: 1x1
  Pixels (1, code-size=3): [1]

The GIF specification (https://www.w3.org/Graphics/GIF/spec-gif89a.txt) states for the Graphic Control Extension "The scope of this extension is the first graphic rendering block to follow". The generated GIF has a delay set only on some images, the others should have the default behaviour (no delay).



Actual results:

The animation shows 7 frames, with the red pixels being shown for the same time as the white pixels (total time 3.5s).


Expected results:

The animation should show only four frames, with no red visible (total time 2s).

Testing in Google Chrome shows that is is correctly applying the 0.5s delay only to the images that follow the Graphic Control Extension, with the other frames showing briefly due to a minimum delay being enforced (Firefox is doing this too).

Comment 1

[Robert Ancell]

I found this behaviour due to writing a a GIF test suite [1], please let me know if this might be of use in Firefox or if there are any particular cases that I could add.

[1] https://github.com/robert-ancell/pygif/tree/master/test-suite

Comment 2

[Robert Ancell]

See bug 1511298 about related issue of non-zero delay.

Comment 3

[Robert Ancell]

Attachment: Animation that shows the graphic control extension being applied to images it shouldn't (the red frames in the image).

This is a larger image showing the issue, generated with the following code:

#!/usr/bin/python

import gif

width = 40
height = 40

writer = gif.Writer (open ('animate-delay-not-reset.gif', 'wb'))
writer.write_header ()
writer.write_screen_descriptor (2*width, 2*height, has_color_table = True, depth = 2)
writer.write_color_table ([(0, 0, 0), (255, 255, 255), (255, 0, 0), (0, 255, 0)], 2)
writer.write_netscape_extension (loop_count = 0)
writer.write_graphic_control_extension (gif.DisposalMethod.KEEP, delay_time = 50)
writer.write_image (2*width, 2*height, 2, ([ 1 ] * width + [ 0 ] * width) * height + [ 0 ] * (2 * width) * height)
writer.write_image (width, height, 2, [ 2 ] * width * height, width, 0)
writer.write_graphic_control_extension (gif.DisposalMethod.KEEP, delay_time = 50)
writer.write_image (width, height, 2, [ 1 ] * width * height, width, 0)
writer.write_image (width, height, 2, [ 2 ] * width * height, width, height)
writer.write_graphic_control_extension (gif.DisposalMethod.KEEP, delay_time = 50)
writer.write_image (width, height, 2, [ 1 ] * width * height, width, height)
writer.write_image (width, height, 2, [ 2 ] * width * height, 0, height)
writer.write_graphic_control_extension (gif.DisposalMethod.KEEP, delay_time = 50)
writer.write_image (width, height, 2, [ 1 ] * width * height, 0, height)
writer.write_trailer ()

Comment 4

[Robert Ancell]

Attachment: What the animation should look like

Comment 5

[Andrew Osmond [:aosmond] (he/him)]

I confirmed the behaviour difference with Chrome. In nsGIFDecoder2::EndImageFrame, we should probably reset mGIFStruct.delay_time to 0.

Comment 6

[Andrew Osmond [:aosmond] (he/him)]

try: https://treeherder.mozilla.org/#/jobs?repo=try&revision=0a5f550496523030ba7b334b668e58dfe2ffc247

Comment 7

[Andrew Osmond [:aosmond] (he/him)]

Attachment: Bug 1511290 - Reset the GIF frame delay time between frames.

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/d83d88a474ce
Reset the GIF frame delay time between frames. r=tnikkel

Comment 9

[Natalia Csoregi [:nataliaCs]]

https://hg.mozilla.org/mozilla-central/rev/d83d88a474ce