Question

I want to create an object that moves (like people are moving or elastic springs), when moving, the shape of the object will be changed. And I do not know how to create a 3D model shape changes in XNA 4.0. Can you help me?? Thanks!

Answer 1

I might be able to give you some beginner-to-beginner advice.

I just learned how to make a model from this example and based on your quesiton I applied an additional scale transform to one of the bones to see if I could manipulate its size the same way I can its position, and it did work.

So I’m implying the answer to your question may be that while a model’s vertex data remains constant you can make it change shape using Scale transforms.

Here’s my model:

using Microsoft.Xna.Framework;
using Microsoft.Xna.Framework.Content;
using Microsoft.Xna.Framework.Graphics;

namespace SimpleAnimation
{
    public class Body
    {
        Model bodyModel;
        ModelBone headBone;
        ModelBone bodyBone;
        Matrix headTransform;
        Matrix bodyTransform;
        Matrix[] boneTransforms;

        public Body()
        {
            HeadScale = 1;
        }

        public void Load(ContentManager content)
        {
            // Load the tank model from the ContentManager.
            bodyModel = content.Load<Model>("body");

            // Look up shortcut references to the bones we are going to animate.
            headBone = bodyModel.Bones["head"];
            bodyBone = bodyModel.Bones["body"];

            // Store the original transform matrix for each animating bone.
            headTransform = headBone.Transform;
            bodyTransform = bodyBone.Transform;

            // Allocate the transform matrix array.
            boneTransforms = new Matrix[bodyModel.Bones.Count];
        }

        public void Draw(Matrix world, Matrix view, Matrix projection)
        {
            // Set the world matrix as the root transform of the model.
            bodyModel.Root.Transform = world;

            // Calculate matrices based on the current animation position.
            Matrix headRotation = Matrix.CreateRotationX(HeadRotation);
            Matrix headScale = Matrix.CreateScale(HeadScale);
            Matrix bodyRotation = Matrix.CreateRotationX(BodyRotation);

            // Apply matrices to the relevant bones.
            headBone.Transform = headScale * headRotation * headTransform;
            bodyBone.Transform = bodyRotation * bodyTransform;

            // Look up combined bone matrices for the entire model.
            bodyModel.CopyAbsoluteBoneTransformsTo(boneTransforms);

            // Draw the model.
            foreach (ModelMesh mesh in bodyModel.Meshes)
            {
                foreach (BasicEffect effect in mesh.Effects)
                {
                    effect.World = boneTransforms[mesh.ParentBone.Index];
                    effect.View = view;
                    effect.Projection = projection;

                    effect.EnableDefaultLighting();
                }

                mesh.Draw();
            }
        }

        public float HeadRotation { get; set; }

        public float HeadScale { get; set; }

        public float BodyRotation { get; set; }
    }
}