SDWebImageWebPCoder: High memory usage in RNFI

Hi,

I’m using SDWebImageWebPCoder with react-native-fast-image and I found that the memory usage is quite high. We use non-animated WebP images but it seems like RNFI uses SDAnimatedImageView to load the images. After profiling I found both _canvas and imageRef in safeAnimatedImageFrameAtIndex are retained. Which makes sense I guess since the canvas is reused for the animation. However for images this causes unnecessary memory usage.

As a temporary workaround I altered animatedImageFrameAtIndex so it releases the canvas after the final frame of the animation (which for an image is immediately)

- (UIImage *)animatedImageFrameAtIndex:(NSUInteger)index {
    UIImage *image;
    if (index >= _frameCount) {
        return nil;
    }
    SD_LOCK(_lock);
    image = [self safeAnimatedImageFrameAtIndex:index];
    SD_UNLOCK(_lock);
    
    if (index + 1 >= _frameCount) {
        CGContextRelease(_canvas);
        _canvas = NULL;
    }

    return image;
}

I don’t think this is a great workaround since it impacts the behavior for animated WebP images (but it may be unnecessary to keep two copies of the image in memory?) so I wondered if there is another way to reduce the memory usage of WebP in SDWebImage and possibly improve RNFI.