How to draw polygons with CGPath?

Question

I have been reading thru the documentation however it is not immediatly clear to me how to draw a polygon using CGPath. All I need to do is to draw CGPath around something like this:

__
\  \ 
 \  \
  \__\

Could anyone please provide an snippet on how to do this?

Additionally I assume CGPathContainsPoint will help me determine if a point is inside such path?, or does the path have to be a solid drawing

Also how can i move the cgpath around? Is this as easy as changing something like the origin just like in cgrect?

Thank you.

-Oscar

Answer 1

You should do it like this:

- (void)drawRect:(CGRect)rect { 

        CGContextRef context = UIGraphicsGetCurrentContext(); 

        CGContextSetStrokeColorWithColor(context, [UIColor redColor].CGColor);
        CGContextSetRGBFillColor(context, 0.0, 0.0, 1.0, 1.0);

        // Draw them with a 2.0 stroke width so they are a bit more visible.
        CGContextSetLineWidth(context, 2.0);

        for(int idx = 0; idx < self.points.count; idx++)
        {

            point = [self.points objectAtIndex:idx];//Edited 
            if(idx == 0)
            {
                // move to the first point
                CGContextMoveToPoint(context, point.x, point.y);
            }
            else
            {
                CGContextAddLineToPoint(context, point.x, point.y);
            }
        }

        CGContextStrokePath(context);
}

Note here, the points is the array of points you want to draw the polygon for. So it should be circular path like: You are drawing a triangle of points (x1, x2, x3) then you should pass into array (x1, x2, x3, x1).

Hope this helps.

Answer 2

This is an example of how to create a triangle using CGPath, you only have to put the points.

var path = CGPathCreateMutable()
CGPathMoveToPoint(path, nil, 0, 0) //start from here
CGPathAddLineToPoint(path, nil, 20, 44) 
CGPathAddLineToPoint(path, nil, 40, 0) 
CGPathAddLineToPoint(path, nil, 0, 0)

//and to use in SpriteKit, for example

var tri = SKShapeNode(path: path) 
var color = NSColor.blueColor()
tri.strokeColor = color
tri.fillColor = color

This is the result

Answer 3

See Apple's QuartzDemo application. It has code for doing this, as well as many other Quartz drawing functions.

Answer 4

Draelach's answer updated to Swift 4:

let path = CGMutablePath()
path.move(to: CGPoint(x: 0, y: 0))
path.addLine(to: CGPoint(x: 20, y: 44))
path.addLine(to: CGPoint(x: 40, y: 0))
path.addLine(to: CGPoint(x: 0, y: 0))

let tri = SKShapeNode(path: path)

Answer 5

Stanford's CS193P class on iPhone had a project called HelloPoly that might be exactly what you want - see class home page for the spec and then see the video for how it was implemented (and google solutions from people who did the assignment).