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Object Orientation

Jan 24, 2009 at 2:33 AM
I need some help and know that you guys can help. I'm using the "SpawnPrimitive" method to shoot arrows from where ever the camera is. Unfortunately, I can't get the arrows to go in the direction that the camera is looking. At first, I couldn't even get the arrows to shoot out from the same side that the camera is looking at. So, I changed the orientation in my SpawnPrimitive call (the second parameter) to use Matrix.Identity and it works. However, if I turn to the side or in a different direction, the arrows still come out in front of me, but they're turned in the direction they were originally. They look like I'm shooting them sideways. I need help getting my arrows turned to look like I'm shooting them straight instead of on their side. The "ArrowObject" is simply a BoxObject with a different name. I'm trying to keep all of my objects separated for special customization.

Here is the code I'm using.

PhysicObject physObj = SpawnPrimitive(cCamera.cameraPosition, Matrix.Identity);

private PhysicObject SpawnPrimitive(Vector3 pos, Matrix ori)
            Vector3 sideLengths = new Vector3(1.0f, 1.0f, 3.0f);
            PhysicObject physicObj = new ArrowObject(this, arrowModel, sideLengths, ori, pos);

            return physicObj;

Thanks in advance...
Jan 27, 2009 at 2:11 PM
The orientation of the objects should be the inverse of the view matrix (Camera orientation).

Matrix arrowOrientation = Matrix.Invert(cCamera.ViewMatrix); // Get the inverse view matrix.
arrowOrientation.Translation = Vector3.Zero; // We don't want any translation added to the arrow.

If you don't have the view-matrix available you can create an orientation matrix using:

Matrix orientation = Matrix.Identity;
orientation.Forward = <The direction you want it to point>;
orientation.Right = Vector3.Normalize(Vector3.Cross(orientation.Forward, Vector3.Up)); // Vector3.Up can be replaced with whatever the up-vector of your world is.
orientation.Up = Vector3.Normalize(Vector3.Cross(orientation.Right, orientation.Forward));

Im pretty sure that code will do the trick. If you get them upside-down or something like that just switch "Cross(orientation.Forward, Vector3.Up)" for "Cross(Vector3.Up, orientation.Forward)".
Hope this helps.
Jan 27, 2009 at 10:57 PM
I tried your suggestions, but still with no luck. The arrows still fly in sideways, backwards, etc... However, when I shoot a sphere object using the same code, the sphere always shoots out in the same direction the camera is looking. It never turns as it's coming out.
Jan 28, 2009 at 1:16 AM
I got it working finally.

        public ArrowObject(Game game, Model model, Vector3 sideLengths, Matrix orientation, Vector3 position) : base(game, model)
            body = new Body();
            collision = new CollisionSkin(body);

                new Box(-0.5f * sideLengths, orientation, sideLengths),
                new MaterialProperties(0.8f, 0.8f, 0.7f));
            body.CollisionSkin = this.collision;
            body.MoveTo(position, Matrix.Identity);
            this.scale = sideLengths;

        public override void ApplyEffects(BasicEffect effect)
            Vector3 color = new Vector3(205, 133, 63);
            color /= 255.0f;
            effect.DiffuseColor = color;

Matrix camRotMatrix = Matrix.CreateFromYawPitchRoll(Yaw, Pitch, Roll);

HandleInput( ):

PhysicObject physObj = SpawnPrimitive(cCamera.cameraPosition, cCamera.camRotMatrix);

SpawnPrimitive( ):
PhysicObject physicObj = new ArrowObject(this, arrowModel, new Vector3(1.0f, 1.0f, 3.0f), ori, pos);