How to render view into image faster?

Question

I\'m making magnifier app, which allows an user touch the screen and move his finger, there will be a magnifier with his finger path. I implement it with take a screenshot a

Answer 1

No. In iOS6, renderInContext: is the only way. It is slow. It uses the CPU.

Ways to render UIKit content

renderInContext:

[view.layer renderInContext:UIGraphicsGetCurrentContext()];

• Requires iOS 2.0. It runs in the CPU.
• It doesn't capture views with non-affine transforms, OpenGL, or video content.
• If an animation is running, you can have the option of capturing:
  • view.layer, which captures the final frame of the animation.
  • view.presentationLayer, which captures the current frame of the animation .

snapshotViewAfterScreenUpdates:

UIView *snapshot = [view snapshotViewAfterScreenUpdates:YES];

• Requires iOS 7.
• It is the fastest method.
• The view contents are immutable. Not good if you want to apply an effect.
• It captures all content types (UIKit, OpenGL, or video).

resizableSnapshotViewFromRect:afterScreenUpdates:withCapInsets

[view resizableSnapshotViewFromRect:rect afterScreenUpdates:YES withCapInsets:edgeInsets]

• Requires iOS 7.
• Same as snapshotViewAfterScreenUpdates: but with resizable insets. content is also immutable.

drawViewHierarchyInRect:afterScreenUpdates:

[view drawViewHierarchyInRect:rect afterScreenUpdates:YES];

• Requires iOS 7.
• It draws in the current context.
• According to session 226 it is faster than renderInContext:.

See WWDC 2013 Session 226 Implementing Engaging UI on iOS about the new snapshotting APIs.

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If it is any help, here is some code to discard capture attempts while one is still running.

This throttles block execution to one at a time, and discards others. From this SO answer.

dispatch_semaphore_t semaphore = dispatch_semaphore_create(1);
dispatch_queue_t renderQueue = dispatch_queue_create("com.throttling.queue", NULL);

- (void) capture {
    if (dispatch_semaphore_wait(semaphore, DISPATCH_TIME_NOW) == 0) {
        dispatch_async(renderQueue, ^{
            // capture
            dispatch_semaphore_signal(semaphore);
        });
    }
}

What is this doing?

• Create a semaphore for one (1) resource.
• Create a serial queue.
• DISPATCH_TIME_NOW means the timeout is none, so it returns non zero immediately on red light. Thus, not executing the if content.
• If green light, run the block asynchronously, and set green light again.