coil-kt/coil

Consider adding workaround for U + gainmap + hardware bitmap bug

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#2094 opened on Jan 31, 2024

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 (2 comments) (0 reactions) (0 assignees)Kotlin (11,779 stars) (757 forks)batch import
help wanted

Description

Prior to Android V there exists a bug where when:

  1. A decode to Config.HARDWARE is requested
  2. The image format is A8 / gray8
  3. The device supports A8 hardware buffers
  4. The device is using OpenGL

Then the decode fails. As A8 images are extremely rare, this hadn't come up before. However, with the addition of gainmap images the usage of A8 "images" became much more common as a common space/quality tradeoff for the gainmap is to use a8 and provide only luminance modulation as a result. In this scenario it becomes quite possible for all 4 of the above conditions to be hit.

However, it is rather easy to both detect the presence of the bug (simply try to copy an A8 bitmap to Config.HARDWARE - if null is returned the bug is present) and to workaround it in a decently efficient means by simply decoding to non-hardware first, converting the A8 gainmap to 8888, and then copying the result to HARDWARE and returning that. This is not dissimilar to how decoding directly to HARDWARE works, so performance impact should be minimal. See the Glide implementation of both here: https://github.com/bumptech/glide/pull/5357

If nothing is done about this then the failure mode is simply that the decoding of the gainmap portion fails, but the primary image is still successfully returned. As in, the behavior simply matches what Android T did, prior to the introduction of gainmaps. So the failure mode is quite forgiving.

Contributor guide

Tech stack
kotlinandroid
Domain
mobile
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
KotlinAndroid developmentBitmap ConfigurationsCoil library basics
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Implement the workaround described in the issue. Refer to the Glide implementation at https://github.com/bumptech/glide/pull/5357 for details. The fix involves detecting the bug by trying to copy an A8 bitmap to Config.HARDWARE and if null is returned, decode to non hardware, convert A8 gainmap to 8888, then copy to hardware. Look at Coil's BitmapFactoryDecoder or similar classes responsible for hardware bitmap decoding.