如何使用 Core Graphics 绘制具有自定义样式的线？

Question

I'm currently drawing a line using Core Graphics. It's really bare bones and simple.

- (void)drawRect:(CGRect)rect {
    CGContextRef c = UIGraphicsGetCurrentContext();
    CGFloat red[4] = {1.0f, 0.0f, 0.0f, 1.0f};
    CGContextSetStrokeColor(c, red);
    CGContextBeginPath(c);
    CGContextMoveToPoint(c, 5.0f, 5.0f);
    CGContextAddLineToPoint(c, 300.0f, 600.0f);
    CGContextSetLineWidth(c, 25);
    CGContextSetLineCap(c, kCGLineCapRound);
    CGContextStrokePath(c);
}

This works well. Let's say that we wanted to draw a custom style line. Say we wanted to imitate the style of a crayon for example. And that the designer handed your crayon style images: http://imgur.com/a/N40ig

To do accomplish this effect I think I need to do something like this:

1. Create a special colored versions of crayonImage1-crayonImage4

2. Every time you add a line to line you use one of the crayonImages

3. You alternate the crayonImages every time you draw a point.

Step 1 makes sense. I can use the following method:

- (UIImage *)image:(UIImage *)img withColor:(UIColor *)color {    
    // begin a new image context, to draw our colored image onto
    UIGraphicsBeginImageContext(img.size);

    // get a reference to that context we created
    CGContextRef context = UIGraphicsGetCurrentContext();

    // set the fill color
    [color setFill];

    // translate/flip the graphics context (for transforming from CG* coords to UI* coords
    CGContextTranslateCTM(context, 0, img.size.height);
    CGContextScaleCTM(context, 1.0, -1.0);

    // set the blend mode to color burn, and the original image
    CGContextSetBlendMode(context, kCGBlendModeColorBurn);
    CGRect rect = CGRectMake(0, 0, img.size.width, img.size.height);
    CGContextDrawImage(context, rect, img.CGImage);

    // set a mask that matches the shape of the image, then draw (color burn) a colored rectangle
    CGContextClipToMask(context, rect, img.CGImage);
    CGContextAddRect(context, rect);
    CGContextDrawPath(context,kCGPathFill);

    // generate a new UIImage from the graphics context we drew onto
    UIImage *coloredImg = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    //return the color-burned image
    return coloredImg;
}

I'm unsure how I can complete steps 2 and 3. Is there an API in CoreGraphics for setting an image as the point of line? If so what is it and how can I use it?

Thanks in advance,

-David

Answer 1

Start with the following example: http://www.ifans.com/forums/showthread.php?t=132024

But for brushes, don't draw a line. Simply draw the brush image using CGContextDrawImage.

Basically, you simply draw an image for every touch.