Iphone – Create a UIImage from two other UIImages on the iPhone

iphoneuiimage

I'm trying to write an animation on the iPhone, without much success, getting crashes and nothing seems to work.

What I wanna do appears simple, create a UIImage, and draw part of another UIImage into it, I got a bit confused with the context and layers and stuff.

Could someone please explain how to write something like that (efficiently), with example code?

Best Answer

For the record, this turns out to be fairly straightforward - everything you need to know is somewhere in the example below:

+ (UIImage*) addStarToThumb:(UIImage*)thumb
{
   CGSize size = CGSizeMake(50, 50);
   UIGraphicsBeginImageContext(size);

   CGPoint thumbPoint = CGPointMake(0, 25 - thumb.size.height / 2);
   [thumb drawAtPoint:thumbPoint];

   UIImage* starred = [UIImage imageNamed:@"starred.png"];

   CGPoint starredPoint = CGPointMake(0, 0);
   [starred drawAtPoint:starredPoint];

   UIImage* result = UIGraphicsGetImageFromCurrentImageContext();
   UIGraphicsEndImageContext();

   return result;
}

Related Solutions

Ios – How to create a colored 1×1 UIImage on the iPhone dynamically

You can use CGContextSetFillColorWithColor and CGContextFillRect for this:

Swift

extension UIImage {
    class func image(with color: UIColor) -> UIImage {
        let rect = CGRectMake(0.0, 0.0, 1.0, 1.0)
        UIGraphicsBeginImageContext(rect.size)
        let context = UIGraphicsGetCurrentContext()

        CGContextSetFillColorWithColor(context, color.CGColor)
        CGContextFillRect(context, rect)

        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return image
    }
}

Swift3

extension UIImage {
    class func image(with color: UIColor) -> UIImage {
        let rect = CGRect(origin: CGPoint(x: 0, y:0), size: CGSize(width: 1, height: 1))
        UIGraphicsBeginImageContext(rect.size)
        let context = UIGraphicsGetCurrentContext()!

        context.setFillColor(color.cgColor)
        context.fill(rect)

        let image = UIGraphicsGetImageFromCurrentImageContext()
        UIGraphicsEndImageContext()

        return image!
    }
}

Objective-C

+ (UIImage *)imageWithColor:(UIColor *)color {
    CGRect rect = CGRectMake(0.0f, 0.0f, 1.0f, 1.0f);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();

    CGContextSetFillColorWithColor(context, [color CGColor]);
    CGContextFillRect(context, rect);

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    return image;
}

R – Converting a CGLayer to a transparent UIImage and PNG file in CoreGraphics iphone

I just dealt with this. Don't draw a background on the CGLayer and then set the background of the UIView to:

self.backgroundColor = [UIColor clearColor];

That should do it and your png will have a transparent background.

Best Answer

Related Solutions

Ios – How to create a colored 1×1 UIImage on the iPhone dynamically

R – Converting a CGLayer to a *transparent* UIImage and PNG file in CoreGraphics iphone

Related Topic

R – Converting a CGLayer to a transparent UIImage and PNG file in CoreGraphics iphone