How to fix "Optimization Opportunities"

Question

I'm using xcode 12. I wrote extension UI View as below:

@IBInspectable
public var shadowRadius: CGFloat {
    get {
        return layer.shadowRadius
    }
    set {
        layer.shadowRadius = newValue
    }
}

@IBInspectable
public var shadowOpacity: Float {
    get {
        return layer.shadowOpacity
    }
    set {
         layer.shadowOpacity = newValue
    }
}

@IBInspectable
public var shadowOffset: CGSize {
    get {
        layer.shadowOffset
    }
    set {
         layer.shadowOffset = newValue
    }
}

@IBInspectable
public var shadowColor: UIColor {
    get {
        return UIColor(cgColor: layer.shadowColor ?? UIColor.clear.cgColor)
    }
    
    set {
        layer.shadowColor = newValue.cgColor
    }
}

Things works fine but when I debug view, I saw some purple warnings like this.

x-xcode-debug-views://7f8fd2258020?DBGViewDebuggerLaunchSessionParameter=7f8fd2258020: runtime: Optimization Opportunities: The layer is using dynamic shadows which are expensive to render. If possible try setting shadowPath, or pre-rendering the shadow into an image and putting it under the layer.

Can someone explain this to me and help me to get rid of it??

Answer 1

Setting shadowPath

One solution is to "guide" the shadow rendering by setting the shadowPath explicitly to your needs, eg.:

yourViewWithShadow.layer.shadowPath = UIBezierPath(rect: yourViewWithShadow.bounds).cgPath

Make sure you're setting the frame at the right time!

Cache rasterization

Another solution is to cache the rasterization:

yourViewWithShadow.layer.shouldRasterize = true
yourViewWithShadow.layer.rasterizationScale = UIScreen.main.scale

Hope this helps you to eliminate expensive calculations.