Slow performance in UIScrollView when create CIImage from data directly.

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Untitled.trace.zip

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MTKView solves this issue.
But it has a limitation of the image size to render.

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#74

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UIImageView is optimized also for CIImage.
It uses itself CIContext internally to display CIImage.
However, how the performance is going on depends on CIImage's backing storage.

And in this case, UIImageView is embedded in UIScrollView.
Scrolling is fine because the canvas size won't change.
Zooming is worst because the canvas size will change every frame.
While this, UIImageView redraws the image using CIContext.

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#105