Draw a rectangle inside a circle with respect to its center

Question

I am trying to place a CGPath over a circle at a given angle. The path looks more like a rectangle. When I finished creating my path, I move to the center of the circle and draw the path from it. But I want to place the left-center of the rectangle to align with the center of the circle, not the top-left. I guess, I should calculate the origin of the rectangle with respect to the given angle by applying some formula, I have no idea how to do it.

 //My logic to draw the circle goes here
....
    //My custom rect drawing logic is inside the CreatePath method
    CGPath customRectPath = CreatePath(size);
    context.TranslateCTM(center.X, center.Y);//I am sure this is where I am doing it wrong
    context.RotateCTM((float)(angle));
    context.AddPath(customRectPath);
    context.DrawPath(CGPathDrawingMode.EOFill);

The image should explain what I am trying to say.

Start [here](https://stackoverflow.com/a/8536553/1971013) I'm sure you can work it out on your own. — meaning-matters, Aug 14 '17 at 12:06

meowgoesthedog · Accepted Answer · 2017-08-25T10:25:20.657

1

TranslateCTM sets the translation of the top-left corner of your rectangle, not the midpoint of the left side (which you want). To do this, simply take away half the rectangle's height from the y-offset:

context.TranslateCTM(center.X, center.Y - size.Height / 2);

edited Aug 25 '17 at 10:25

answered Aug 14 '17 at 14:48

meowgoesthedog

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score 0 · Answer 2 · answered Aug 14 '17 at 17:25

You should create the rectangle so that it is relative to the rotation origin.

Eg the corners of the rect

0, - width / 2      // top left
size , - width / 2  // top right
size, width /2,     // bottom right
0, width / 2        // bottom left

Any shape that you intend to transform should be created relative to the intended rotation and scale origin.

Draw a rectangle inside a circle with respect to its center

2 Answers2