Cocoa Touch - Adding texture with overlay view

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
}