Core Graphics context

A Core Graphics context is a canvas which we can draw in it and set some properties like the line thickness.

Making a context

To make a context, we use the UIGraphicsBeginImageContextWithOptions() C function. Then, when we are done with drawing, we just call UIGraphicsEndImageContext() to end the context:

Swift

let size = CGSize(width: 256, height: 256)

UIGraphicsBeginImageContextWithOptions(size, false, 0)

let context = UIGraphicsGetCurrentContext()

// drawing code here

UIGraphicsEndImageContext()

Objective-C

CGSize size = [CGSize width:256 height:256];

UIGraphicsBeginImageContextWithOptions(size, NO, 0);

CGContext *context = UIGraphicsGetCurrentContext();

// drawing code here

UIGraphicsEndImageContext();

In the code above, we passed 3 parameters to the UIGraphicsBeginImageContextWithOptions() function:

1. A CGSize object which stores the whole size of the context (the canvas)

2. A boolean value which if it is true, the context will be opaque

3. An integer value which sets the scale (1 for non-retina, 2 for retina and 3 for retina HD screens). If set to 0, the system automatically handles the scale based on the target device.

Swift

let image = UIGraphicsGetImageFromCurrentImageContext()
imageView.image = image //assuming imageView is a valid UIImageView object

Objective-C

UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
imageView.image = image; //assuming imageView is a valid UIImageView object