iOS CGContext Edge isn't antialiased - ios

Question

I'm trying to draw a rectangle that has a 15 degree angle splitting two colors down the center but the line between them is pixelated. I've tried different blend options and can't seem to figure out how to make this look clean.
This is what the header looks like now
Does anyone know how I can make the line between them look clean?
if (!_backgroundImageView.image) {
CGFloat width = CGRectGetWidth(self.bounds);
CGFloat height = CGRectGetHeight(self.bounds);
CGFloat tWidth = 0.26794919243f/*tan(15 degrees)*/ * height;
UIGraphicsBeginImageContext(CGSizeMake(width, height));
CGContextRef context = UIGraphicsGetCurrentContext();
if (_color1) {
CGContextSetFillColorWithColor(context, _color1.CGColor);
CGContextMoveToPoint(context, 0, 0);
CGContextAddLineToPoint(context, 1.0f + RoundPixelValue((width + tWidth) / 2.0f), 0);
CGContextAddLineToPoint(context, 1.0f + RoundPixelValue((width - tWidth) / 2.0f), height);
CGContextAddLineToPoint(context, 0, height);
CGContextFillPath(context);
}
if (_color2) {
CGContextSetFillColorWithColor(context, _color2.CGColor);
CGContextMoveToPoint(context, width, 0);
CGContextAddLineToPoint(context, RoundPixelValue((width + tWidth) / 2.0f) - 1.0f, 0);
CGContextAddLineToPoint(context, RoundPixelValue((width - tWidth) / 2.0f) - 1.0f, height);
CGContextAddLineToPoint(context, width, height);
CGContextFillPath(context);
}
_backgroundImageView.image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
}

Answer 1

The main issue here is that you're not creating the context with the correct scale.
Instead of using UIGraphicsBeginImageContext use UIGraphicsBeginImageContextWithOptions like so:
UIGraphicsBeginImageContextWithOptions(CGSizeMake(width, height), YES, 0);
Specifying a scale of 0 sets it to the scale factor of the device screen.
This should eliminated most of the aliasing artifacts.