Draw arc with 2 points and center of the circle

Question

I have two points of circle and center of this circle. I want to draw an arc between these points. Method drawArc is to simple and doesn't fit my purpose. Anybody help?

I know that exists meny functions to draw Arc, but I can't fint suitable — CarolusPl, Nov 16 '10 at 17:13

score 28 · Answer 1 · edited Jul 14 '13 at 00:25

28

You can use Canvas.drawArc, but you must compute the arguments it needs:

Lets say that the center of the circle is (x0, y0) and that the arc contains your two points (x1, y1) and (x2, y2). Then the radius is: r=sqrt((x1-x0)(x1-x0) + (y1-y0)(y1-y0)). So:

int r = (int)Math.sqrt((x1-x0)*(x1-x0) + (y1-y0)*(y1-y0));
int x = x0-r;
int y = y0-r;
int width = 2*r;
int height = 2*r;
int startAngle = (int) (180/Math.PI*atan2(y1-y0, x1-x0));
int endAngle = (int) (180/Math.PI*atan2(y2-y0, x2-x0));
canvas.drawArc(x, y, width, height, startAngle, endAngle);

Good luck!

edited Jul 14 '13 at 00:25

Alex Lockwood

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answered Nov 22 '10 at 15:19

botismarius

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FYI: This code would work a bit better if you used `float` instead of `int` variables. PI=3.14, Square Roots, etc. You could be creating a lot of zeros if you stick with `int` types. – Dec 18 '12 at 22:30
4

in theory yes. however, drawArc() has int parameters. – botismarius Dec 19 '12 at 22:26
Note that r = Math.hypot(x1-x0, y1 - 0) – vdolez Nov 01 '16 at 08:19
Currently this `canvas.drawArc()` has 2 parameters more and is designed for API 21. Use overriden version if you need < 21. – CoolMind May 14 '20 at 07:49

score 2 · Answer 2 · answered Nov 16 '10 at 17:13

Graphics.drawArc expects the following parameters:

x
y
width
height
startAngle
arcAngle

Given your arc start and end points it is possible to compute a bounding box where the arc will be drawn. This gives you enough information to provide parameters: x, y, width and height.

You haven't specified the desired angle so I guess you could choose one arbitrarily.

Draw arc with 2 points and center of the circle

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