ios - Core Graphics CGImage mask not affecting -

what i'm trying have text label 'cut' text-shaped hole through view. i've tried using self.mask = uilabel refused position text correctly i'm approaching through core graphics.

here's code isn't working (in draw(_ rect: cgrect)):

    let context = (uigraphicsgetcurrentcontext())!      // set mask background color     context.setfillcolor(uicolor.black.cgcolor)     context.fill(rect)      context.savegstate()       let paragraphstyle = nsmutableparagraphstyle()     paragraphstyle.alignment = .center      let attributes = [         nsparagraphstyleattributename: paragraphstyle,         nsfontattributename: uifont.systemfont(ofsize: 16, weight: uifontweightmedium),         nsforegroundcolorattributename: uicolor.white     ]      let string = nsstring(string: "login")      // wouldn't vertically align calculate string size , create new rect in vertically aligned     let size = string.size(attributes: attributes)     let position = cgrect(         x: rect.origin.x,         y: rect.origin.y + (rect.size.height - size.height) / 2,         width: rect.size.width,         height: size.height     )      context.translateby(x: 0, y: rect.size.height)     context.scaleby(x: 1, y: -1)     string.draw(         in: position,         withattributes: attributes     )      let mask = (context.makeimage())!      context.restoregstate()      // redraw created mask     context.clear(rect)      context.savegstate()     // !!!! below line problem     context.clip(to: rect, mask: mask)     context.restoregstate() 

essentially i've created code create cgimage (the mask variable) mask want apply whole image.

the marked line when replaced context.draw(mask, in: rect) (to view mask) correctly displays. mask shows (correctly) as:

:

however once try apply mask (using context.clip(to: rect, mask: mask)) nothing happens!. actual result:

desired result is:

but reason mask not being correctly applied.

---

this code seems should work i've read docs on , on again. i've additionally tried create mask in separate cgcontext didn't work. when tried convert cgimage (mask) cgcolorspacecreatedevicegray() using .copy(colorspace:), returned nil. i've been @ 2 days appreciated

if want label have translucent text, can use blend modes instead of masks.

public class knockoutlabel: uilabel {     public override func draw(_ rect: cgrect) {         let context = uigraphicsgetcurrentcontext()!         context.setblendmode(.clear)          self.drawtext(in: rect)     } } 

make sure set isopaque false though; default view assumes opaque, since use opaque background color.