CODEWITHSUNDEEP
iosiphoneswiftuiimageviewcalayer
Davidgs
Davidgs

Reputation: 419

iOS Screen coordinates and scaling

I'm trying to draw on top of an image in a CALayer and am having trouble with where the drawing shows up on different size displays.

func drawLayer(){
    let circleLayer = CAShapeLayer()
    let radius: CGFloat = 30
    let x = Thermo.frame.origin.x
    let y = Thermo.frame.origin.y
    let XX = Thermo.frame.width
    let YY = Thermo.frame.height
    print("X: \(x) Y: \(y) Width: \(XX) Height: \(YY)")
    circleLayer.path = UIBezierPath(roundedRect: CGRect(x: 0, y: 0, width: 2.0 * radius, height: 2.0 * radius)  , cornerRadius: radius).CGPath
    circleLayer.fillColor = UIColor.redColor().CGColor
    circleLayer.shadowOffset = CGSizeMake(0, 3)
    circleLayer.shadowRadius = 5.0
    circleLayer.shadowColor = UIColor.blackColor().CGColor
    circleLayer.shadowOpacity = 0.8
    circleLayer.frame = CGRectMake(0, 410, 0, 192);
    self.Thermo.layer.addSublayer(circleLayer)
    circleLayer.setNeedsDisplay()
}

That draws a circle, in the correct place ... for an iPhone 6s. But when the enclosing UIImageView component is scaled for a smaller device, well, to clearly doesn't. I added the print() to see what the image size, and position was and ... well, it's exactly the same on every device I run it on X: 192.0 Y: 8.0 Width: 216.0 Height: 584.0 but clearly it's being scaled by the constraints in the AuoLayout manager.

So, my question is how can I figure out the proper radio and position for different screen sizes if I can't use the enclosing View's size and position since that seems to never change?

Here is the image I am starting with, in a UIImageView, and trying to draw over. Base Image Im of course trying to color it in based on data from an external device. Any suggestions/sample code most appreciated!

Upvotes: 0

Views: 1075

Answers (1)

Earl Grey
Earl Grey

Reputation: 7466

CALayer and its subclasses incl. CAShapeLayer have a property 

var contentsScale: CGFloat

From class reference :

For layers you create and manage yourself, you must set the value of this property yourself based on the resolution of the screen and the content you are providing. Core Animation uses the value you specify as a cue to determine how to render your content.

So what you need to do is set the scale on the layer and you get the scale of the device from UIDevice class

circleLayer.scale = UIScreen.mainScreen().scale

Upvotes: 2

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