Draw rectangle with clear background on top of imageView - ios

Question

I am trying to draw a rectangle with a random border color with a clear background on top of an imageView. I need to loop through a set of co-ordinates and add appropriate rectangles to my image. I can't manage to get the rectangle background colour to be clear. Code below:
// the draw class
class Draw: UIView {
override init(frame: CGRect) {
super.init(frame: frame)
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func draw(_ rect: CGRect) {
let h = rect.height
let w = rect.width
let color:UIColor = Palette.getRandomColour()
//var drect = CGRect(x: (w * 0.25),y: (h * 0.25),width: (w * 0.5),height: (h * 0.5))
let drect = CGRect(x: rect.minX ,y: rect.minY , width: w, height: h)
let bpath:UIBezierPath = UIBezierPath(rect: drect)
UIColor.clear.setFill()
color.set()
bpath.stroke()
print("it ran")
NSLog("drawRect has updated the view")
}
}
// and in my viewDidLoad
for bp in sbp {
if let master = Bodyparts.getID(bp.masterid) {
let width = master.x2 - master.x1
let height = master.y2 - master.y1
let k = Draw(frame: CGRect(origin: CGPoint(x: master.x1, y: master.y1), size: CGSize(width: width, height: height)))
self.imgView.addSubview(k)
}
}

Answer 1

You need to set the background to clear. Here is a playground that you can copy and paste:
import PlaygroundSupport
import UIKit
class Draw: UIView {
override init(frame: CGRect) {
super.init(frame: frame)
backgroundColor = .clear
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
override func draw(_ rect: CGRect) {
let h = rect.height
let w = rect.width
let color:UIColor = .red
let drect = CGRect(x: rect.minX ,y: rect.minY , width: w, height: h)
let bpath:UIBezierPath = UIBezierPath(rect: drect)
UIColor.clear.setFill()
color.set()
bpath.stroke()
}
}
let d = Draw(frame: CGRect(x: 0, y: 0, width: 100, height: 100))
let view = UIView(frame: CGRect(x: 0, y: 0, width: 200, height: 200))
view.backgroundColor = .green
view.addSubview(d)
PlaygroundPage.current.liveView = view

Answer 2

I'm not exactly sure if mean a transparent center of the rect by clear but you can use the following method.
You would need to set the style of the Paint to stroke, to draw a box instead of a filled rect. Basically you will draw a bounding box if you use the Paint.Style.Stroke option of your Paint.
// Give the canvas an image to draw on
val canvas: Canvas = bitmap?.let { Canvas(it) }!!
// Test points for rect
val left = 100f
val right = 300f
val top = 100f
val bottom = 500f
// Paint definition for bounding box
var borderPaint: Paint = Paint()
borderPaint.strokeWidth = 10f
borderPaint.color = Color.GREEN
borderPaint.style = Paint.Style.STROKE
// Draw border
canvas.drawRect(left, top, right, bottom+100, borderPaint)
// Show the bitmap on display
viewBinding.imageView.setImageBitmap(bitmap)