Image rendering is slow

[yu-t]

@muukii For large images cgContext.draw(cgImage, in: CGRect(origin: .zero, size: canvasSize)) in public func render(resolution: Resolution = .full) -> UIImage takes too long, about a minute.
Can you please suggest how this can be fixed?

[ntnmrndn]

Are you using the simulator ? The simulator is very slow, but real device should do it in seconds at most.

[yu-t]

@ntnmrndn I use a real device. iPhone XS, 14.0.1.
I try with this photo: https://unsplash.com/photos/ETeQcrvs0No

[Sam-Spencer]

@muukii It appears that this function runs on the main thread sometimes, causing the UI to appear blocked. Additionally, the logs show that (for some reason) a CGImage is unavailable from the supplied UIImage. According to Apple's documentation, this can happen when converting between a UIImage and a CIImage... are you addressing this in v2?

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It seems that some of the issues also have to do with the TransitionPatch dependency?

[muukii]

@Sam-Spencer
Thanks.

Firstly, the above function can be run in background-thread.

public func render(resolution: Resolution = .full) -> UIImage

Lager image takes a long time, it's unavoidable.
So would you try to run in backgorund-thread?

In order to render large(full-size) image, we need to use CPU rendering in my opinion.
And some more image manipulations need to use CoreGraphics.
That's why we use CGImage.

[muukii]

And I thought we could get something optimizations.
If the image only needs cropping, we can get the final image without using CoreGraphics manipulations.

[muukii]

This PR might faster this.
#76