How to draw a gradient line (fading in/out) with Core Graphics/iPhone?

Question

I know how to draw a simple line:

CGContextSetRGBStrokeColor(context, 1.0, 1.0, 1.0, 1.0);
CGContextMoveToPoint(context, x, y);
CGContextAddLineToPoint(conte         


        

Answer 1

You can use Core Animation layers. You can use a CAShaperLayer for your line by settings its path property and then you can use a CAGradientLayer as a layer mask to your shape layer that will cause the line to fade.

Replace your CGContext... calls with calls to CGPath... calls to create the line path. Set the path field on the layer using that path. Then in your gradient layer, specify the colors you want to use (probably black to white) and then set the mask to be the line layer like this:

 [gradientLayer setMask:lineLayer];

What's cool about the gradient layer is that is allows you to specify a list of locations where the gradient will stop, so you can fade in and fade out. It only supports linear gradients, but it sounds like that may fit your needs.

Let me know if you need clarification.

EDIT: Now that I think of it, just create a single CAGradientLayer that is the width/height of the line you desire. Specify the gradient colors (black to white or black to clear color) and the startPoint and endtPoints and it should give you what you need.