Question

So I have successfully made a ray the represents the mouse unprojected into the world, and now I need to check if that ray can intersect with a quad object, here is the code I use to get the ray:

public Ray GetMouseRay()
    {
        Vector2 mousePosition = new Vector2(cursor.getX(), cursor.getY());

        Vector3 nearPoint = new Vector3(mousePosition, 0);
        Vector3 farPoint = new Vector3(mousePosition, 1);

        nearPoint = viewport.Unproject(nearPoint, projectionMatrix, viewMatrix, Matrix.Identity);
        farPoint = viewport.Unproject(farPoint, projectionMatrix, viewMatrix, Matrix.Identity);

        Vector3 direction = farPoint - nearPoint;
        direction.Normalize();

        return new Ray(nearPoint, direction);
    }

And similarly, this is my quad struct, which I use to draw a “cube world” in 3d space.
public struct Quad
{
public Vector3 Origin;
public Vector3 UpperLeft;
public Vector3 LowerLeft;
public Vector3 UpperRight;
public Vector3 LowerRight;
public Vector3 Normal;
public Vector3 Up;
public Vector3 Left;

    public VertexPositionNormalTexture[] Vertices;
      public int[] Indexes;
    public short[] Indexes;


    public Quad( Vector3 origin, Vector3 normal, Vector3 up, 
        float width, float height )
    {
        Vertices = new VertexPositionNormalTexture[4];
        Indexes = new short[6];
        Origin = origin;
        Normal = normal;
        Up = up;

        // Calculate the quad corners
        Left = Vector3.Cross( normal, Up );
        Vector3 uppercenter = (Up * height / 2) + origin;
        UpperLeft = uppercenter + (Left * width / 2);
        UpperRight = uppercenter - (Left * width / 2);
        LowerLeft = UpperLeft - (Up * height);
        LowerRight = UpperRight - (Up * height);

        FillVertices();
    }

    private void FillVertices()
    {
        // Fill in texture coordinates to display full texture
        // on quad
        Vector2 textureUpperLeft = new Vector2( 0.0f, 0.0f );
        Vector2 textureUpperRight = new Vector2( 1.0f, 0.0f );
        Vector2 textureLowerLeft = new Vector2( 0.0f, 1.0f );
        Vector2 textureLowerRight = new Vector2( 1.0f, 1.0f );

        // Provide a normal for each vertex
        for (int i = 0; i < Vertices.Length; i++)
        {
            Vertices[i].Normal = Normal;
        }

        // Set the position and texture coordinate for each
        // vertex
        Vertices[0].Position = LowerLeft;
        Vertices[0].TextureCoordinate = textureLowerLeft;
        Vertices[1].Position = UpperLeft;
        Vertices[1].TextureCoordinate = textureUpperLeft;
        Vertices[2].Position = LowerRight;
        Vertices[2].TextureCoordinate = textureLowerRight;
        Vertices[3].Position = UpperRight;
        Vertices[3].TextureCoordinate = textureUpperRight;

        // Set the index buffer for each vertex, using
        // clockwise winding
        Indexes[0] = 0;
        Indexes[1] = 1;
        Indexes[2] = 2;
        Indexes[3] = 2;
        Indexes[4] = 1;
        Indexes[5] = 3;
    }
}

I found that the ray class has a method intersects() which takes a plane struct as a parameter, and the plane struct takes a normal and distance from origin in the constructor, but my planes have a position and normal instead of just distance from origin, so I can’t convert them. How can I detect if my ray is intersecting my quad struct?

Edit:
I realize that I can’t use the plane struct, as it is not of finite size and does not include corners, as my quad does. I need to find a way now to detect if this ray is intersecting the quad I have created…

Thanks for reading, I realize this question is a bit lengthy, and thanks in advance.

Answer 1

I’m not sure exactly what they mean by “distance along the normal from the origin”, but I would assume it just mean the distance from the origin. You can get that from the length property on a Vector3.

If that doesn’t work, there is also a constructor for plane which takes three points on the plane:

public Plane (
     Vector3 point1,
     Vector3 point2,
     Vector3 point3
)

You can use this with any 3 points on the plane, such as the corners of your quad, to create a plane.