如何为屏幕上显示的图像获取准确的持续时间计时器？

Question

I am trying to get an accurate time interval for an image that is displayed on the screen for only a short duration.

Let's say that I want an image to be displayed for around 150ms on the screen, I know that most iOS devices have a variable refresh rate (usually between 20-60Hz) so this will mean that it is impossible to hit that 150ms perfectly on the mark. What I would like to know, is there a way to measure the exact time interval for the image being displayed? Ideally, I'd like for this to be accurate to within a few milliseconds.

Thanks in advance for any help I can get!

Answer 1

If you use Metal, you can add a "presented handler" block to be called when the drawable has been presented (shown on screen). Use the -addPresentedHandler: method of MTLDrawable to do that. In that block, you can query the presentedTime property of the drawable.

If you use that to first show an image and then clear the image (display black or white or whatever), then you can compare the two presented time values to determine how long the image was displayed.

In addition to that, you can schedule presentation of a drawable for a specific time, using the -presentDrawable:atTime: (or, depending on your needs, -presentDrawable:afterMinimumDuration: ) method of MTLCommandBuffer .

Answer 2

You should look at using a CADisplayLink . It's a timer that's synced to the screen refresh cycle.