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Episode #288 | 9 minutes | published on July 21, 2017 | Uses swift-3.0, Xcode-8.3

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core graphics

In this episode, Sam shows how to draw text using Core Graphics. With this technique you can easily add text to images for pre-rendering, a technique we will see in another episode in this series.

This episode is part of a series: Dive Into Core Graphics.

1. Intro 2 min

2. Basic Shapes 7 min

3. Paths 17 min

4. Colors 9 min

5. Gradients 11 min

6. Clipping Paths 6 min

7. Context Transforms 10 min

8. Images 7 min

9. Text 9 min

10. Offscreen Rendering 12 min

11. Custom CALayer 13 min

12. Pie Progress View 7 min

13. Watermarking Photos 6 min

14. Working in AppKit 8 min

Setting up

We will just fill our view with white, then define a string we can draw.

guard let context = UIGraphicsGetCurrentContext() else { return }

let colorSpace = CGColorSpaceCreateDeviceRGB()
let color = CGColor(colorSpace: colorSpace, components: [1, 1, 1, 1])!

context.setFillColor(color)
context.fill(bounds)

let string = "Hello World"

Defining Text Attributes

To configure text color, font, alignment, and other text attributes, we will use NSAttributedString. This takes a dictionary of attributes to apply to the string.

let paragraph = NSMutableParagraphStyle()
paragraph.alignment = .center

let attributes: [String: Any] = [
    NSFontAttributeName: UIFont.systemFont(ofSize: 40),
    NSForegroundColorAttributeName: UIColor.blue,
    NSParagraphStyleAttributeName: paragraph
]

Using NSString’s Drawing Method

NSString can draw itself, which is the simplest approach.

(string as NSString).draw(at: CGPoint(x: 20, y: 20), withAttributes: attributes)

Drawing with NSAttributedString

We can also draw an attributed string similarly:

let attributedString = NSMutableAttributedString(string: string, attributes: attributes)
attributedString.addAttribute(NSFontAttributeName, 
    value: UIFont.systemFont(ofSize: 40, weight: UIFontWeightBold),
    range: NSRange(location: 6, length: 5))

let size = attributedString.size()
attributedString.draw(in: AVMakeRect(aspectRatio: size, insideRect: bounds))

Drawing with UILabel

Another quick way to do this (on iOS) is top leverage UILabel’s drawing.

let label = UILabel()
label.attributedText = attributedString
label.drawText(in: bounds)

View on Github

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