Why Are Core Graphics Lines Not Aligned? - ios

Question

Quick question: This code should produce (among others) 4 lines that are perpendicular to each other. However, when run, the lines are all off by a small amount.
for i in 0..<60 {
CGContextSaveGState(ctx)
CGContextTranslateCTM(ctx, rect.width / 2, rect.height / 2)
CGContextRotateCTM(ctx, CGFloat(6.0 * Double(i) * M_PI / 180))
CGContextSetStrokeColorWithColor(ctx, UIColor.grayColor().CGColor)
CGContextMoveToPoint(ctx, 50, 50)
if (i % 5 == 0) {
CGContextSetLineWidth(ctx, 3.0)
CGContextAddLineToPoint(ctx, 30, 30)
}
else {
CGContextSetLineWidth(ctx, 2.0)
CGContextAddLineToPoint(ctx, 40, 40)
}
CGContextStrokePath(ctx)
CGContextRestoreGState(ctx)
}
Still learnings Core Graphics, so sorry if this is simple.
Regards, Brandon
EDIT 1:
Here is what I am getting:

Answer 1

If I am assuming it correctly, you want to draw ticks that look like ticks on a watch face.
If you let it draw only one iteration, e.g.
for i in 0..<1
You will see that the first tick starts at some angle. This is happening because you are drawing line from (x=50, y=50) to (x=30, y=30)
Try changing it to (x=50, y=0)(x=30, y=0)
for i in 0..<60 {
CGContextSaveGState(ctx)
CGContextTranslateCTM(ctx, rect.width / 2, rect.height / 2)
CGContextRotateCTM(ctx, CGFloat(6.0 * Double(i) * M_PI / 180))
CGContextSetStrokeColorWithColor(ctx, UIColor.grayColor().CGColor)
CGContextMoveToPoint(ctx, 50, 0) // <-- changed here
if (i % 5 == 0) {
CGContextSetLineWidth(ctx, 3.0)
CGContextAddLineToPoint(ctx, 30, 0) // <-- changed here
}
else {
CGContextSetLineWidth(ctx, 2.0)
CGContextAddLineToPoint(ctx, 40, 0) // <-- changed here
}
CGContextStrokePath(ctx)
CGContextRestoreGState(ctx)
}
Result