How to create and draw a visual swipe gesture

I'd like to try implementing a visual swipe for an iPhone project, like they do in some games, like Fruit Ninja. As you drag your finger around the screen, it leaves a trail that disappears after a while. I would think that you could have a fixed number of points in the "chain" and as new points are added to the front, old 开发者_开发百科ones are removed from the rear. I can see using -touchesMoved to generate new points and an NSMutableArray to keep track of the points. I just can't imaging what method I'd use to actually draw the segments. Would I make one CALayer and draw a line connecting the active points? Or use some other view object and join them together at the points...

Any ideas?

Something like this would work, if you had populated 'points' with CGPoints. Caveat: this is a quick cut, paste and edit job - so there will probably be errors. Also, I use stl::vector for 'points'. You may want to use some other structure.

CGContextRef context = UIGraphicsGetCurrentContext();
CGMutablePathRef dataPath = CGPathCreateMutable();
bool firstPoint = YES;

for (int i=0; i < points.size(); ++i)
    {
    CGPoint point = points[i];
    if (firstPoint)
        {
        CGPathMoveToPoint(dataPath, NULL, point.x, point.y);
        firstPoint = NO;
        }
    else
        {
        CGPathAddLineToPoint(dataPath, NULL, point.x, point.y);
        }
    }

CGContextSetRGBStrokeColor( context, 1.0, 0.0, 0.0, 1.0);
CGContextSetLineWidth( context, 5);
CGContextBeginPath( context );
CGContextAddPath( context, dataPath );
CGContextDrawPath( context, kCGPathStroke);

CGPathRelease(dataPath);