RotatePointAroundPoint

Introduction

RotatePointAroundPoint is a method that can easily rotate one point around another. This method uses the System.Math.Atan2 method to calculate angles. All functionality provided by this method can also be obtained through System.Math.Atan2.

Code Example

The following code creates a Sprite which rotates about the origin when the user holds down the space bar. Add the following at class scope:

Sprite sprite;

Add the following to Initialize after initializing FlatRedBall:

sprite = SpriteManager.AddSprite("redball.bmp");
sprite.X = 3;

Add the following to Update:

 if (InputManager.Keyboard.KeyDown(Microsoft.Xna.Framework.Input.Keys.Space))
 {
     const float rotationRate = 10f; // in radians per second
     const float xToRotateAbout = 0;
     const float yToRotateAbout = 0;

     // The starting point is the current location of the Sprite
     float newX = sprite.X;
     float newY = sprite.Y;

     // Rotate the point and store the new position in 
     // newX and newY
     FlatRedBall.Math.MathFunctions.RotatePointAroundPoint(
         xToRotateAbout, yToRotateAbout, 
         ref newX, ref newY, 
         rotationRate * TimeManager.SecondDifference);

     // Set the Sprite's new position to newX and newY
     sprite.X = newX;
     sprite.Y = newY;
 }

RotatePointAroundPoint.png