CGBitmapContextCreate: unsupported parameter combination. How to pass kCGImageAlphaNoneSkipFirst [duplicate] - ios

Question

This question already has answers here:
kCGImageAlphaNone unresolved identifier in swift
(2 answers)
Closed 7 years ago.
I originally wrote this App (GitHub) in Obj-C, but need to convert it to Swift. Upon converting I've been having trouble getting the Context for the Bitmap created.
Error Message:
Whiteboard[2833] <Error>: CGBitmapContextCreate: unsupported parameter combination: 8 integer bits/component; 24 bits/pixel; 3-component color space; kCGImageAlphaNone; 1500 bytes/row.
Originally I had this:
self.cacheContext = CGBitmapContextCreate (self.cacheBitmap, size.width, size.height, 8, bitmapBytesPerRow, CGColorSpaceCreateDeviceRGB(), kCGImageAlphaNoneSkipFirst);
And now I have:
self.cacheContext = CGBitmapContextCreate(self.cacheBitmap!, UInt(size.width), UInt(size.height), 8, bitmapBytesPerRow, CGColorSpaceCreateDeviceRGB(), CGBitmapInfo.ByteOrder32Little);
I believe the issue has to do with CGBitmapInfo.ByteOrder32Little, but I'm not sure what to pass. Is there a way to pass kCGImageAlphaNoneSkipFirst as a CGBitmapInfo?
Full Source:
//
// WhiteBoard.swift
// Whiteboard
//
import Foundation
import UIKit
class WhiteBoard: UIView {
var hue: CGFloat
var cacheBitmap: UnsafeMutablePointer<Void>?
var cacheContext: CGContextRef?
override init(frame: CGRect) {
self.hue = 0.0;
// Create a UIView with the size of the parent view
super.init(frame: frame);
// Initialize the Cache Context of the bitmap
self.initContext(frame);
// Set the background color of the view to be White
self.backgroundColor = UIColor.whiteColor();
// Add a Save Button to the bottom right corner of the screen
let buttonFrame = CGRectMake(frame.size.width - 50, frame.size.height - 30, 40, 25);
let button = UIButton();
button.frame = buttonFrame;
button.setTitle("Save", forState: .Normal);
button.setTitleColor(UIColor.blueColor(), forState: .Normal);
button.addTarget(self, action: "downloadImage", forControlEvents: .TouchUpInside);
// Add the button to the view
self.addSubview(button);
}
required init(coder aDecoder: NSCoder) {
self.hue = 0.0;
super.init(coder: aDecoder)
}
func initContext(frame: CGRect)-> Bool {
let size = frame.size; // Get the size of the UIView
var bitmapByteCount: UInt!
var bitmapBytesPerRow: UInt!
// Calculate the number of bytes per row. 4 bytes per pixel: red, green, blue, alpha
bitmapBytesPerRow = UInt(size.width * 4);
// Total Bytes in the bitmap
bitmapByteCount = UInt(CGFloat(bitmapBytesPerRow) * size.height);
// Allocate memory for image data. This is the destination in memory where any
// drawing to the bitmap context will be rendered
self.cacheBitmap = malloc(bitmapByteCount);
// Create the Cache Context from the Bitmap
self.cacheContext = CGBitmapContextCreate(self.cacheBitmap!, UInt(size.width), UInt(size.height), 8, bitmapBytesPerRow, CGColorSpaceCreateDeviceRGB(), CGBitmapInfo.ByteOrder32Little);
// Set the background as white
CGContextSetRGBFillColor(self.cacheContext, 1.0, 1.0, 1.0, 1.0);
CGContextFillRect(self.cacheContext, frame);
CGContextSaveGState(self.cacheContext);
return true;
}
// Fired everytime a touch event is dragged
override func touchesMoved(touches: NSSet, withEvent event: UIEvent) {
let touch = touches.anyObject() as UITouch;
self.drawToCache(touch);
}
// Draw the new touch event to the cached Bitmap
func drawToCache(touch: UITouch) {
self.hue += 0.005;
if(self.hue > 1.0) {
self.hue = 0.0;
}
// Create a color object of the line color
let color = UIColor(hue: CGFloat(self.hue), saturation: CGFloat(0.7), brightness: CGFloat(1.0), alpha: CGFloat(1.0));
// Set the line size, type, and color
CGContextSetStrokeColorWithColor(self.cacheContext, color.CGColor);
CGContextSetLineCap(self.cacheContext, kCGLineCapRound);
CGContextSetLineWidth(self.cacheContext, CGFloat(15));
// Get the current and last touch point
let lastPoint = touch.previousLocationInView(self) as CGPoint;
let newPoint = touch.locationInView(self) as CGPoint;
// Draw the line
CGContextMoveToPoint(self.cacheContext, lastPoint.x, lastPoint.y);
CGContextAddLineToPoint(self.cacheContext, newPoint.x, newPoint.y);
CGContextStrokePath(self.cacheContext);
// Calculate the dirty pixels that needs to be updated
let dirtyPoint1 = CGRectMake(lastPoint.x-10, lastPoint.y-10, 20, 20);
let dirtyPoint2 = CGRectMake(newPoint.x-10, newPoint.y-10, 20, 20);
self.setNeedsDisplay();
// Only update the dirty pixels to improve performance
//self.setNeedsDisplayInRect(dirtyPoint1);
//self.setNeedsDisplayInRect(dirtyPoint2);
}
// Draw the cachedBitmap to the UIView
override func drawRect(rect: CGRect) {
// Get the current Graphics Context
let context = UIGraphicsGetCurrentContext();
// Get the Image to draw
let cacheImage = CGBitmapContextCreateImage(self.cacheContext);
// Draw the ImageContext to the screen
CGContextDrawImage(context, self.bounds, cacheImage);
}
// Download the image to the camera roll
func downloadImage() {
// Get the Image from the CGContext
let image = UIImage(CGImage: CGBitmapContextCreateImage(self.cacheContext));
// Save the Image to their Camera Roll
UIImageWriteToSavedPhotosAlbum(image, self, "image:didFinishSavingWithError:contextInfo:", nil);
}
func image(image: UIImage, didFinishSavingWithError error: NSError, contextInfo: UnsafeMutablePointer<Void>) {
if(!error.localizedDescription.isEmpty) {
UIAlertView(title: "Error", message: "Error Saving Photo", delegate: nil, cancelButtonTitle: "Ok").show();
}
}
}

Answer 1

In Objective-C, you would simply cast to the other enum type, like this:
(CGBitmapInfo)kCGImageAlphaNoneSkipFirst
In Swift, you have to do it like this:
CGBitmapInfo(CGImageAlphaInfo.NoneSkipFirst.rawValue)
Welcome to the wild and wacky world of Swift numerics. You have to pull the numeric value out of the original CGImageAlphaInfo enumeration with rawValue; now you can use that numeric value in the initializer of the CGBitmapInfo enumeration.
EDIT It's much simpler in iOS 9 / Swift 2.0, where you can just pass CGImageAlphaInfo.NoneSkipFirst.rawValue directly into CGBitmapContextCreate, which now just expects an integer at this spot.