Cocoa Touch - Adding texture with overlay view - cocoa-touch

Question

I have a set of tiles as UIViews that have a programmable background color, and each one
can be a different color. I want to add texture, like a side-lit bevel, to each one. Can this be done with an overlay view or by some other method?
I'm looking for suggestions that don't require a custom image file for each case.

Answer 1

This may help someone, although this was pieced together from other topics on SO.
To create a beveled tile image with an arbitrary color for normal and for retina display, I made a beveled image in photoshop and set the saturation to zero, making a grayscale image called tileBevel.png
I also created one for the retina display (tileBevel#2x.png)
Here is the code:
+ (UIImage*) createTileWithColor:(UIColor*)tileColor {
int pixelsHigh = 44;
int pixelsWide = 46;
UIImage *bottomImage;
if([UIScreen respondsToSelector:#selector(scale)] && [[UIScreen mainScreen] scale] == 2.0) {
pixelsHigh *= 2;
pixelsWide *= 2;
bottomImage = [UIImage imageNamed:#"tileBevel#2x.png"];
}
else {
bottomImage = [UIImage imageNamed:#"tileBevel.png"];
}
CGImageRef theCGImage = NULL;
CGContextRef tileBitmapContext = NULL;
CGRect rectangle = CGRectMake(0,0,pixelsWide,pixelsHigh);
UIGraphicsBeginImageContext(rectangle.size);
[bottomImage drawInRect:rectangle];
tileBitmapContext = UIGraphicsGetCurrentContext();
CGContextSetBlendMode(tileBitmapContext, kCGBlendModeOverlay);
CGContextSetFillColorWithColor(tileBitmapContext, tileColor.CGColor);
CGContextFillRect(tileBitmapContext, rectangle);
theCGImage=CGBitmapContextCreateImage(tileBitmapContext);
UIGraphicsEndImageContext();
return [UIImage imageWithCGImage:theCGImage];
}
This checks to see if the retina display is used, sizes the rectangle to draw in, picks the appropriate grayscale base image, set the blending mode to overlay, then draws a rectangle on top of the bottom image. All of this is done inside a graphics context bracketed by the BeginImageContext and EndImageContext calls. These set the current context needed by the UIImage drawRect: method. The Core Graphics functions need the context as a parameter, which is obtained by a call to get the current context.
And the result looks like this:

Answer 2

If you want to preserve the alpha channel of the source image, just add this to jim's code before the fill rect:
// Apply mask
CGContextTranslateCTM(tileBitmapContext, 0, rectangle.size.height);
CGContextScaleCTM(tileBitmapContext, 1.0f, -1.0f);
CGContextClipToMask(tileBitmapContext, rectangle, bottomImage.CGImage);

Answer 3

Swift 3 solution, essentially based on Jim's answer with Scriptease's addition, and some minor changes:
class func image(bottomImage: UIImage, topImage: UIImage, tileColor: UIColor) -> UIImage? {
let pixelsHigh: CGFloat = bottomImage.size.height
let pixelsWide: CGFloat = bottomImage.size.width
let rectangle = CGRect.init(x: 0, y: 0, width: pixelsWide, height: pixelsHigh)
UIGraphicsBeginImageContext(rectangle.size);
bottomImage.draw(in: rectangle)
if let tileBitmapContext = UIGraphicsGetCurrentContext() {
tileBitmapContext.setBlendMode(.overlay)
tileBitmapContext.setFillColor(tileColor.cgColor)
tileBitmapContext.scaleBy(x: 1.0, y: -1.0)
tileBitmapContext.clip(to: rectangle, mask: bottomImage.cgImage!)
tileBitmapContext.fill(rectangle)
let theCGImage = tileBitmapContext.makeImage()
UIGraphicsEndImageContext();
if let theImage = theCGImage {
return UIImage.init(cgImage: theImage)
}
}
return nil
}