How to draw the vertices on a CGContext CGMutablePathRef? - ios

Question

I am drawing a set of connected lines as the user enters clicks to specify vertices. I am build a CGMutablePathRef
- (void)addPointToCGMPR: (CGPoint)p
forNewPolygon: (BOOL)newPoly
{
if (newPoly)
{
CGPathMoveToPoint(cgmpr, NULL, p.x, p.y);
}
else
{
CGPathAddLineToPoint(cgmpr, NULL, p.x, p.y);
}
[self setNeedsDisplay];
}
drawRect: is then called after each point is entered, and the context CGMutablePathRef is added to a CGContext for display
- (void)drawRect:(CGRect)rect
{
// Set up a context to display
CGContextRef context = UIGraphicsGetCurrentContext();
CGContextAddPath(context, cgmpr);
CGContextSetLineWidth(context, 1);
CGContextStrokePath(context);
// If NOT empty then Close the context so that box comparison can occur later
if (!CGContextIsPathEmpty(context))
{
CGContextClosePath(context);
}
}
I am getting lines on the screen as one would expect. My trouble is that after the user picks the first point there is nothing rendered on the screen and the user is left not knowing if the system got his first pick until after the second point is entered. I would like for the system to render the first point even before the next point is entered. I would also like for the system to render each one of the vertices picked in a visually distinct way - right now I am not getting vertices rendered, only lines. Is there a way to ask the CGContext to render points? Is there a way to specify the style in which these points are rendered? Thanks.

Answer 1

You're free to draw whatever you want to represent the points: a small square, a small circle, an image of a pushpin, etc. You already know how to draw into a context; just loop over your points and draw them however you want them to appear. I personally tend to use CGContextFillEllipseInRect for things like this. For each point, make a rect that surrounds the point and draw it:
CGFloat pointSize = 4;
CGRect pointRect = CGRectMake(point.x - pointSize / 2, point.y - pointSize / 2, pointSize, pointSize);
CGContextFillEllipseInRect(context, pointRect);

Answer 2

No. You'll need to render them yourself by adding another CGPath to describe whatever you want to represent the vertex. Since you'll probably draw this often, you may want to render it to a CGLayer so you can easily copy it where you need it. You could also draw your vertices onto CALayers so you can easily move them around. But it's up to you to design and manage this part of the drawing.