AxisAlignedRectangle

Introduction

The AxisAlignedRectangle is a PositionedObject which is used for unrotated bounding box collision. This is preferred over Polygon collision if Sprites are not rotated due to speed and memory usage considerations. AxisAlignedRectangles share many similarities with the other shape classes (Circle, Line, and Polygon). For general information about shapes, see the ShapeManager wiki entry. For information on using AxisAlignedRectangles in Glue, see this page. AxisAlignedRectangles do not support being filled-in. They can only render as an outline. To render a solid rectangle, look at using Sprites with the Color ColorOperation

What does "axis aligned" mean?

The "AxisAligned" part of AxisAlignedRectangle indicates that the sides of the rectangle are "axis aligned". In other words, the top, bottom, left, and right are all parallel to either the X or Y axes. AxisAlignedRectangles are always axis aligned for performance reasons. Therefore, if you rotate an AxisAlignedRectangle (set its RotationZ), this will have no impact on the collision behavior or its visible representation. If your game requires rotation, you should use the Polygon class. Of course, performance will suffer slightly if collision performance is a consideration for your game. For more information on axis alignment and a discussion of axis aligned object rotation and children positions, see this page.

AxisAlignedRectangles are PositionedObjects

The AxisAlignedRectangle class inherits from PositionedObject. This means that all properties which are available to PositionedObjects (excluding rotation) are available to AxisAlignedRectangles. For more information, see the PositionedObject page.

Creating an AxisAlignedRectangle

AxisAlignedRectangles are created through the ShapeManager. The following code creates an AxisAlignedRectangle through the ShapeManager and resizes it: Add the following using statement

using FlatRedBall.Math.Geometry;

Create the instance:

// AxisAlignedRectangles added this way are Visible by default and also managed
// by the ShapeManager.
AxisAlignedRectangle rectangle = ShapeManager.AddAxisAlignedRectangle();
rectangle.ScaleX = 5;
rectangle.ScaleY = 7;

SimpleRectangle.png

Relationship with ShapeManager

See ShapeManager wiki entry.

Move (Solid) Collision

Solid or moving collision can be performed with AxisAlignedRectangles as well as Polygons and Circles. The following code creates three AxisAlignedRectangles - one controlled by the player, one which can be pushed, and one which is is immovable. Add the following using statements:

using FlatRedBall.Input;
using FlatRedBall.Math.Geometry;

Add the following at class scope:

AxisAlignedRectangle playerRectangle;
AxisAlignedRectangle movableBlockRectangle;
AxisAlignedRectangle solidRectangle;

Add the following in Initialize after Initializing FlatRedBall:

 playerRectangle = ShapeManager.AddAxisAlignedRectangle();
 playerRectangle.X = -3;
 playerRectangle.Color = Color.Yellow;

 movableBlockRectangle = ShapeManager.AddAxisAlignedRectangle();
 movableBlockRectangle.Color = Color.Red;

 solidRectangle = ShapeManager.AddAxisAlignedRectangle();
 solidRectangle.ScaleX = solidRectangle.ScaleY = 4;
 solidRectangle.X = 7;

Add the following in Update:

 InputManager.Keyboard.ControlPositionedObject(playerRectangle);

 // player and movable have the same mass
 playerRectangle.CollideAgainstMove(movableBlockRectangle, .5f, .5f);
 // make the solid infinitely more massive than the player
 playerRectangle.CollideAgainstMove(solidRectangle, 0, 1);
 // make the solid infinitely more massive than the movable
 movableBlockRectangle.CollideAgainstMove(solidRectangle, 0, 1);

SolidCollision.png

Determining Collision Side

For information on determining which side an object has collided on, see this page on LastMoveCollisionReposition.

AxisAlignedRectangle Members

• FlatRedBall.Math.Geometry.AxisAlignedRectangle.Bottom
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.CollideAgainst
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.CollideAgainstBounce
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.CollideAgainstMove
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.CollideAgainstMoveSoft
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.Color
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.GetRandomPositionInThis
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.Height
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.KeepThisInsideOf
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.LastMoveCollisionReposition
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.Left
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.RepositionDirections
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.Right
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.Top
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.Width
• FlatRedBall.Math.Geometry.AxisAlignedRectangle.Z

Extra Information

• Axis Alignment and Rotation
• Tile Collision

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