Convert SwiftUI View to UIImage on iOS 14+ - view

Question

I can convert any SwiftUI View to a high resolution UIImage, using the code below. It works great... until... I try to use an image size larger than CGSize(width: 2730, height: 2730).
If I increase the image size to CGSize(width: 2731, height: 2731) or larger, the line:
self.drawHierarchy(in: self.layer.bounds, afterScreenUpdates: true)
in "extension UIView", can no longer draw the UIImage.
Any idea on why there is a size limitation?
One Note: I can overcome the size limitation by uncommenting the 2 lines in the "extension View" and replacing:
self.drawHierarchy(in: self.layer.bounds, afterScreenUpdates: true)
With:
layer.render(in: context.cgContext)
in the "extension UIView"... But THEN "layer.render" will not render image effects such as "blur", SceneKit subviews, or metal. So using "self.drawHierarchy" is a must.
// 1: Set breakpoint on line: print("done") to inspect the high res image
// 2: Run, then tap the image on screen to inspect the highresImage
// 3: repeat after changing the size to CGSize = CGSize(width: 2731, height: 2731)
import SwiftUI
struct ContentView: View {
#State var blurRadius: CGFloat = 4.0
let imageSize: CGSize = CGSize(width: 2730, height: 2730)
var body: some View {
testView
.frame(width: 300, height: 300)
.onTapGesture {
// Adjust blur radius based on high res image scale
blurRadius *= imageSize.width * 0.5/300
// Capture high res image of swiftUI view
let highresImage = testView.asImage(size: imageSize)
// set breakpoint here to inspect the high res image size, quality, etc.
print("done")
// reset blur radius back to 4
blurRadius = 4
}
}
var testView: some View {
ZStack {
Color.blue
Circle()
.fill(Color.red)
}
.blur(radius: blurRadius)
}
}
extension UIView {
func asImage() -> UIImage {
let format = UIGraphicsImageRendererFormat()
format.scale = 1
return UIGraphicsImageRenderer(size: self.layer.frame.size, format: format).image { context in
self.drawHierarchy(in: self.layer.bounds, afterScreenUpdates: true)
//layer.render(in: context.cgContext)
}
}
}
extension View {
func asImage(size: CGSize) -> UIImage {
let controller = UIHostingController(rootView: self)
controller.view.bounds = CGRect(origin: .zero, size: size)
//UIApplication.shared.windows.first!.rootViewController?.view.addSubview(controller.view)
let image = controller.view.asImage()
//controller.view.removeFromSuperview()
return image
}
}

Answer 1

I can't figure out why, but it works for me, after changing the y-coordinate of the view's origin to anything non zero. This may be a bug in UIHostingController.
If you use a very small Int, you can't see the difference, e.g.:
controller.view.bounds = CGRect(origin: CGPoint(x: 0, y: 0.0001), size: size)