#1951: Fix animated WebP decoding issue, including canvas size, the support for dispose method and the duration per frame

[dreampiggy]

New Pull Request Checklist

• I have read and understood the CONTRIBUTING guide

• I have read the Documentation

• I have searched for a similar pull request in the project and found none

• I have updated this branch with the latest master to avoid conflicts (via merge from master or rebase)

• I have added the required tests to prove the fix/feature I am adding - add an new test for ensure animated image array share the same size

• I have updated the documentation (if necessary) - added sd_webpLoopCount(UIImage+WebP.h)

• I have run the tests and they pass

• I have run the lint and it passes (pod lib lint)

This merge request fixes / reffers to the following issues: ...

Pull Request Description

SDWebImage 4.0 add support for animated WebP images. And the UIImage+WebP category use +[UIImage animatedImageWithImages:duration:] to create animated image.

Fixed Bugs:

1. While decoding animated WebP image, for each frame, you need to draw the frame image on the canvas. The older version just use sd_rawWepImageWithData to draw, but the config.input.width/height for this frame does not refer the total image size, it refer to this frame's canvas size(can be smaller than image size). So finally this will lead the final UIImage array (which is used to build animated image) have different size, cause UIImage render strange.

2. CGBitmapInfo should not use 0 for non-alpha channel, you should explicit assign it to kCGImageAlphaNoneSkipLast (with the byte-order bit kCGBitmapByteOrder32Big)

3. The older version animated WeP decoding does not concentrate any diposal method. Which will cause animated WebP images render issue for many images. To fix this, I add a CGBitmapContext before the loop and share it and draw the frames. For each frame, it will clear the frame rect in context only when the background diposal method.

4. +[UIImage animatedImageWithImages:duration:] just use the average duration for each frame, which is not the animated WebP standard. Animated WebP can has different duration per frame. Therefore, I divide the total duration and add image item multiple times to solve this issue.

Known Issues:

1. Currently all the animated WebP showing animation infinity. To solve this, we can get the loop count and set UIImageView's animationRepeatCount property. But UIImageView need use this property with both animationImages and animationDuration. Only set image with an animated UIImage and animationDuration will not work. However sometimes auto-set this property may break user code. So I just add an new property called sd_webpLoopCount at UIImage+WebP.h to get the loop count from WebP data. For nil or static WebP, the default value is 0, otherwise it should become animated WebP loop count.

[codecov-io]

Codecov Report

Merging #1952 into master will increase coverage by 0.82%.
The diff coverage is 79.31%.

@@            Coverage Diff             @@
##           master    #1952      +/-   ##
==========================================
+ Coverage    76.6%   77.42%   +0.82%     
==========================================
  Files          27       27              
  Lines        2513     2631     +118     
==========================================
+ Hits         1925     2037     +112     
- Misses        588      594       +6

Impacted Files	Coverage Δ
Tests/Tests/UIImageMultiFormatTests.m	100% <100%> (ø)	⬆️
SDWebImage/UIImage+WebP.m	75% <72.89%> (+31.7%)	⬆️
SDWebImage/SDWebImageCompat.m	88.23% <90%> (+0.23%)	⬆️
SDWebImage/SDImageCache.m	70.63% <0%> (-3.97%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 041842b...e3ed82f. Read the comment docs.

[worldofnick]

Awesome, how long until this is in?

[bpoplauschi]

I have to trust you @dreampiggy with this PR, this logic is a bit too complicated for me. But let's bring it it.

[dreampiggy]

@bpoplauschi Maybe I can use that Demo project(https://github.com/dreampiggy/AnimatedWebPDemo) with the lastest SD repo and add more WebP images to test.

This fix logic about 1. 2. 3. is nearly the same as #1694.

The last one(5. support duration per frame), it use the simple gcd number of each frame duration and add current frame for multiple times because that UIKit suck at +[UIImage animatedImageWithImages:duration:]. I search the GitHub and found one use the same method for GIF decoding(https://github.com/mayoff/uiimage-from-animated-gif/blob/master/uiimage-from-animated-gif/UIImage%2BanimatedGIF.m). But i'd check it more carefully.

[bpoplauschi]

@dreampiggy I've run the builds, tests and CI, that's why we have them. Seems to be ok, so I merged it. We will found out soon if there are any problems :)