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POQuaternion rotation in XNA
 

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  1. POQuaternion rotation in XNA
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    <p>Am I doing the following right?</p> <p>Well obviously not cause otherwise I wont be posting a question here, but I'm trying to do a Quaternion rotation of a model around another model.</p> <p>Lets say I have a box model that has a vector3 position and a float rotation angle. I also have a frustum shaped model that is pointing towards the box model, with its position lets say 50 units from the box model. The frustum also has a vector3 position and a Quaternion rotation.</p> <p>In scenario 1, the box and frustum are "unrotated". This is all fine and well. In scenario 2, I rotate the box only and I want the frustum to rotate with it (kinda like a chase camera) with the frustum always pointing directly at the box and at the same distance from the box as in the unrotated distance. Obviously if I just rotate the model and the frustum by using Matrix.CreateRotationY() for both the box and the frustum, the frustum is slightly offset to the side. </p> <p>So I thought a Quaternion rotation of the frustum around the box would be best? To this end I have tried the following, with no luck. It draws my models on the screen, but it also draws what looks like a giant box to the screen and no matter how far away I move the camera the box is always in the way</p> <p>For the purpose of testing, I have 3 boxes and their 3 associated frustums In my Game1 class I initialize the box[0] with positions and rotations</p> <pre><code>boxObject[0].Position = new Vector3(10, 10, 10); boxObject[1].Position = new Vector3(10, 10, 10); boxObject[2].Position = new Vector3(10, 10, 10); boxObject[0].Rotation = 0.0f; boxObject[1].Rotation = 45.0f; boxObject[2].Rotation = -45.0f; </code></pre> <p>So all 3 boxes drawn at the same position but at different angles. Then to do the frustums, I initiate their position:</p> <pre><code>float f = 50.0f; frustumObject[0].Position = new Vector3(boxObject[0].Position.X, boxObject[0].Position.Y, boxObject[0].Position.Z + f); frustumObject[1].Position = new Vector3(boxObject[1].Position.X, boxObject[1].Position.Y, boxObject[1].Position.Z + f); frustumObject[2].Position = new Vector3(boxObject[2].Position.X, boxObject[2].Position.Y, boxObject[2].Position.Z + f); </code></pre> <p>And then try and rotate around their associated box model:</p> <pre><code>frustumObject[0].ModelRotation = new Quaternion(boxObject[0].Position.X, boxObject[0].Position.Y, boxObject[0].Position.Z + f, 0); frustumObject[0].ModelRotation = new Quaternion(boxObject[0].Position.X, boxObject[0].Position.Y, boxObject[0].Position.Z + f, 45); frustumObject[0].ModelRotation = new Quaternion(boxObject[0].Position.X, boxObject[0].Position.Y, boxObject[0].Position.Z + f, -45); </code></pre> <p>And finally, to draw the models, I Draw() them in my GameModel class which also has:</p> <pre><code>public Model CameraModel { get; set; } public Vector3 Position { get; set; } public float Rotation { get; set; } public Quaternion ModelRotation { get; set; } public void Draw(Matrix view, Matrix projection) { transforms = new Matrix[CameraModel.Bones.Count]; CameraModel.CopyAbsoluteBoneTransformsTo(transforms); // Draw the model foreach (ModelMesh myMesh in CameraModel.Meshes) { foreach (BasicEffect myEffect in myMesh.Effects) { // IS THIS CORRECT????? myEffect.World = transforms[myMesh.ParentBone.Index] * Matrix.CreateRotationY(Rotation) * Matrix.CreateFromQuaternion(ModelRotation) * Matrix.CreateTranslation(Position); myEffect.View = view; myEffect.Projection = projection; myEffect.EnableDefaultLighting(); myEffect.SpecularColor = new Vector3(0.25f); myEffect.SpecularPower = 16; } myMesh.Draw(); } } </code></pre> <p>Can anyone spot where I am going wrong? Is it because I am doing 2 types of rotations n the Draw()? </p> <blockquote> <p>myEffect.World = transforms[myMesh.ParentBone.Index] * Matrix.CreateRotationY(Rotation) * Matrix.CreateFromQuaternion(ModelRotation) * Matrix.CreateTranslation(Position);</p> </blockquote>
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    1. COWithout delving deeply into the code, the first thing that strikes me (which could be stupid) is the order of the matrices; I think the quaternion should be after the translation. This probably won't fix it, but it's worth a try.
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    2. COThanks, Ill give this a try and let you know how I get on.
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    3. CONope, sorry that didnt do the trick either. Think I will try 2 different Draw() methods, one for the box and one for the frustum (normal rotation in the box Draw and Quartenion rotation in the frustum Draw) and see how that goes.
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