IsPointInside

Introduction

The IsPointInside method returns whether an absolute X/Y position is inside the calling Polygon. This function takes 3D position objects (such as Vector3) but ignores the Z value. Only X and Y are considered.

Code Example

The following code creates a Polygon that is in the shape of a rectangle. When the user moves the cursor in the polygon it turns red; otherwise it is yellow.

Add the following using statements:

using Microsoft.Xna.Framework.Graphics;
using FlatRedBall.Math.Geometry;
using FlatRedBall.Input;

Define the Polygon at class scope:

Polygon polygon;

Add the following in Initializing after initializing FlatRedBall (or CustomInitialize if using Screens):

polygon = Polygon.CreateRectangle(3, 3);
ShapeManager.AddPolygon(polygon);
IsMouseVisible = true;

Add the following in Update (or CustomActivity if using Screens):

if (polygon.IsPointInside(
    InputManager.Mouse.WorldXAt(polygon.Z),
    InputManager.Mouse.WorldYAt(polygon.Z)))
{
    polygon.Color = Color.Red;
}
else
{
    polygon.Color = Color.Yellow;
}

RedRectanglePolygon.png

IsPointInside and ForceUpdateDependencies

The IsPointInside method requires that the Polygon has constructed its internal vertices. This means that you must either:

• Wait for one frame so that the Polygon has a chance to render and have its internal vertices set properly. If your polygon is not rendered or part of the ShapeManager then waiting one frame will not result in the internal vertices being updated.
• Call FlatRedBall.Math.Geometry.Polygon.ForceUpdateDependencies

If neither of the above has happened, then the internal vertices will not be set and this function will always return false.