how to rotate a point around another point

Question

I am writing a game. I need to know how to rotate point a around point b by a given number of degrees. I am writing this in java and it is going to be part of my class, Point.

Sine and cosine may help: http://en.wikipedia.org/wiki/Rotation_matrix — Niklas B., Mar 18 '14 at 21:13
Check out http://www.willamette.edu/~gorr/classes/GeneralGraphics/Transforms/transforms2d.htm. Transformation matrices are the tool you need here; you can encapsulate rotation, translation, scaling, etc. — Jason C, Mar 18 '14 at 21:19
You could take a look at [this example](http://stackoverflow.com/questions/12964983/rotate-image-around-character-java/12971987#12971987) — MadProgrammer, Mar 18 '14 at 21:19

score 18 · Answer 1 · edited Mar 18 '14 at 21:24

18

double x1 = point.x - center.x;
double y1 = point.y - center.y;

double x2 = x1 * Math.cos(angle) - y1 * Math.sin(angle));
double y2 = x1 * Math.sin(angle) + y1 * Math.cos(angle));

point.x = x2 + center.x;
point.y = y2 + center.y;

This approach uses rotation matrices. "point" is your point a, "center" is your point b.

edited Mar 18 '14 at 21:24

Jason C

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answered Mar 18 '14 at 21:18

SDLeffler

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Is the variable angle supposed to be in radians or degrees? – user2277362 Mar 18 '14 at 22:14
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@user2277362 Why not [look it up](http://docs.oracle.com/javase/7/docs/api/java/lang/Math.html)? – Niklas B. Mar 18 '14 at 22:18
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Math.sin and other trig functions use radians. The Math class also has toDegrees() and toRadians() functions. – SDLeffler Mar 18 '14 at 23:25

how to rotate a point around another point

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