Some Lossless WebP files can not be decoded and therefore used

[Maran23]

Tested versions

• Reproducable in Godot 4.6.1

System information

Godot v4.6.1.stable - Windows 11 (build 26100) - Multi-window, 4 monitors - Vulkan (Forward+) - dedicated AMD Radeon RX 6900 XT (Advanced Micro Devices, Inc.; 32.0.21041.1000) - AMD Ryzen 9 5900X 12-Core Processor (24 threads) - 31.92 GiB memory

Issue description

Some WebP Images do not work in Godot. There is always this error:

ERROR: Failed decoding WebP image.
ERROR: core/io/image_loader.cpp:100 - Error loading image: 'res://background.webp'.
ERROR: Error importing 'res://background.webp'.

All of the issues are created with Aseprite 1.3.16.1.

What I found out so far:

• They all works with Chromium, Aseprite and on Windows Image Viewer
• If a high compression level does not work, then most of the lower ones work. Sometimes 0 compression level does not work, while e.g. 1 works.
• It seems that bigger images with non pixel art suffer from this. But not all of them

Steps to reproduce

• Open the attached project, in there are images that do not work
• Some images work with another compression levels, which I added as well

Minimal reproduction project (MRP)

webp-decoder.zip

[Maran23]

I debugged a bit and found out the following:

• background-comp-level-8-works.webp

Correctly detects, that the WebP is lossless (format=2) and has no animation.

Using the webpinfo binary:

File: background-comp-level-8-works.webp
RIFF HEADER:
  File size:   1766
Chunk VP8L at offset     12, length   1754
  Width: 2048
  Height: 512
  Alpha: 1
  Animation: 0
  Format: Lossless (2)
No error detected.

• background-comp-level-9-dont.webp

Same image, I just changed the compression level. Now it detects the WebP format as undefined/mixed (format=0) and with an animation (There is none).

Using the webpinfo binary:

File: background-comp-level-9-dont.webp
RIFF HEADER:
  File size:   1654
Chunk VP8X at offset     12, length     18
  ICCP: 0
  Alpha: 1
  EXIF: 0
  XMP: 0
  Animation: 1
  Canvas size 2048 x 512
Chunk ANIM at offset     30, length     14
  Background color:(ARGB) ff ff ff ff
  Loop count      : 1
Chunk ANMF at offset     44, length   1610
  Offset_X: 0
  Offset_Y: 110
  Width: 2048
  Height: 402
  Duration: 1
  Dispose: 0
  Blend: 1
Chunk VP8L at offset     68, length   1586
  Width: 2048
  Height: 402
  Alpha: 1
  Animation: 0
  Format: Lossless (2)
No error detected.

It seems to use the first VP8X chunk information, which are not right.

I wonder why this happens. But also why all other programs can handle that still. So there must be a combination which we do not handle yet correctly in Godot?

[AThousandShips]

Sounds like:

• Cannot decode WebP images that are lossless and transparent #109558