Drawing text with an MKOverlayRenderer

Question

I'm trying to render text on a map using an MKOverlayRenderer. I have an existing, functional MKOverlayRenderer rendering a set of points, so my only problem is rendering a piece of text for each point within the '-(void)drawMapRect:(MKMapRect)mapRect zoomScale:(MKZoomScale)zoomScale inContext:(CGContextRef)context' function.

All solutions I have found through SO and Google use annotations or UILabels. But I want to have the text drawing code in the same location as the code rendering the points. Also there are about 10,000 points, though I'm ensuring it's not rendering them all at the same time through zoom and bounds checking. I am reasonably sure I don't want to create 10,000 objects with the other solutions.

This is the current test code I have to try to render one of the 'Text Text' items. It is a combination of some of the methods I have found on the net to try to render something.

CGPoint* point = self.pointList.pointArray + pointIndex;
CGContextSetRGBFillColor(context, 1.0, 0.0, 0.0, 1.0);
CGContextSetRGBStrokeColor(context, 1.0, 0.0, 0.0, 1.0);
CGContextSelectFont(context, "Helvetica", 20.f, kCGEncodingFontSpecific);
CGContextSetTextDrawingMode(context, kCGTextFill);
CGAffineTransform xform = CGAffineTransformMake(1.0, 0.0, 0.0, -1.0, 0.0, 0.0);
CGContextSetTextMatrix(context, xform);
CGContextShowTextAtPoint(context, point->x, point->y, "Test Text 1", 11);
CGContextShowTextAtPoint(context, 10, 10, "Test Text 2", 11);
CGContextShowText(context, "Test Text 4", 11);
UIFont* font = [UIFont fontWithName:@"Helvetica" size:12.0];
[@"Test Text 3" drawAtPoint:*point withFont:font];

This is my first SO questions, so sorry if it isn't that correct.

Edit: I just saw the text when zoomed in as far as I can go, so realise I haven't been accounting for the zoom scale. Assuming I need to do a scale transform before rendering to account for it. Haven't solved it currently, but I think I am on my way.

SteveGT SteveGT · Accepted Answer · 2014-10-07T03:28:36

I have solved it. Sorry for posting this, but I was at my wit's end and thought I needed help.

The line that rendered was:

CGContextShowTextAtPoint(context, point->x, point->y, "Test Text 1", 11);

Which is a deprecated function, but I don't know any other way to render to a specific context.

To fix it, the affine transform became:

CGAffineTransform xform = CGAffineTransformMake(1.0 / zoomScale, 0.0, 0.0, -1.0 / zoomScale, 0.0, 0.0);

The other error was that the 'select font' call needed to become:

CGContextSelectFont(context, "Helvetica", 12.f, kCGEncodingMacRoman);

I had copied the other encoding from some example code I had seen on the net, but it causes the text to have wrong characters.

If there is still a way I can do it without using the deprecated CGContextShowTextAtPoint function I would still love to know.

Drawing text with an MKOverlayRenderer

1 Answers