Caleb R Caleb R - 1 month ago 21
iOS Question

How do I draw on an image in Swift?

I need to be able to programmatically draw on an image, and save that image for later use. Say, draw a line on specific x and y coordinates on the image, save the image, and display it onto a simple view controller. How would I go about doing this in Swift? (Preferably Swift 2, I am still in development and haven't updated my mac to Sierra)


Update: Possibly something to do with converting a UIImage to a CGLayer, drawing on it, and then converting it back to a UIImage.

Answer

It's simple:

  1. Make an image graphics context. (Before iOS 10, you would do this by calling UIGraphicsBeginImageContextWithOptions. In iOS 10 there's another way, UIGraphicsImageRenderer, but you don't have to use it if you don't want to.)

  2. Draw (i.e. copy) the image into the context. (UIImage actually has draw... methods for this very purpose.)

  3. Draw your line into the context. (There are CGContext functions for this.)

  4. Extract the resulting image from the context. (For example, if you used UIGraphicsBeginImageContextWithOptions, you would use UIGraphicsGetImageFromCurrentImageContext.) Then close the context.

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