3D Object Morphing in C#

This tutorial demonstrates how to morph one 3D object into another using C# and OpenGL with the OpenTK library Or Unity 3D. We will use vertex interpolation to achieve the morphing effect.

Prerequisites

• Visual Studio installed on your system
• NuGet package manager
• Basic understanding of 3D graphics

Step 1: Setup the Project

Create a new C# Console App project in Visual Studio and add the OpenTK library using NuGet:

Install-Package OpenTK

Step 2: Load 3D Objects

Prepare two OBJ files representing the start and target shapes. Use a library like AssimpNet to load the OBJ files into your application.

Install-Package AssimpNet

Here's how to load a 3D model:

using Assimp;

public class ModelLoader
{
    public List LoadModel(string filePath)
    {
        AssimpContext context = new AssimpContext();
        Scene scene = context.ImportFile(filePath);

        var vertices = new List();
        foreach (var mesh in scene.Meshes)
        {
            foreach (var vertex in mesh.Vertices)
            {
                vertices.Add(new Vector3(vertex.X, vertex.Y, vertex.Z));
            }
        }

        return vertices;
    }
}

Step 3: Interpolate Vertices

Define a function to interpolate between two sets of vertices:

public List InterpolateVertices(List from, List to, float t)
{
    var result = new List();
    for (int i = 0; i < from.Count; i++)
    {
        var interpolated = Vector3.Lerp(from[i], to[i], t);
        result.Add(interpolated);
    }
    return result;
}

Step 4: Render the Morph

Use OpenGL to render the morphing process. Initialize a GameWindow and set up a render loop:

using OpenTK.Graphics.OpenGL;
using OpenTK;

public class MorphingRenderer : GameWindow
{
    private List currentVertices;
    private List startVertices;
    private List endVertices;
    private float morphTime = 0;

    protected override void OnLoad(EventArgs e)
    {
        base.OnLoad(e);
        GL.ClearColor(0.1f, 0.1f, 0.1f, 1.0f);
    }

    protected override void OnUpdateFrame(FrameEventArgs e)
    {
        base.OnUpdateFrame(e);
        morphTime += 0.01f;
        if (morphTime > 1.0f) morphTime = 0;

        currentVertices = InterpolateVertices(startVertices, endVertices, morphTime);
    }

    protected override void OnRenderFrame(FrameEventArgs e)
    {
        base.OnRenderFrame(e);
        GL.Clear(ClearBufferMask.ColorBufferBit | ClearBufferMask.DepthBufferBit);

        GL.Begin(PrimitiveType.Triangles);
        foreach (var vertex in currentVertices)
        {
            GL.Vertex3(vertex);
        }
        GL.End();

        SwapBuffers();
    }
}

Step 5: Run the Application

Load your OBJ models, set up the renderer, and start the application:

static void Main(string[] args)
{
    var loader = new ModelLoader();
    var startModel = loader.LoadModel("start.obj");
    var endModel = loader.LoadModel("end.obj");

    using (var renderer = new MorphingRenderer())
    {
        renderer.startVertices = startModel;
        renderer.endVertices = endModel;
        renderer.Run();
    }
}

Conclusion

In this tutorial, you learned how to morph one 3D object into another using C# and OpenGL. Experiment with different interpolation methods and OBJ models to create unique morphing effects!

Unity 3D version of Morphing

Morphing an OBJ file into another in Unity typically requires loading and interpolating the vertices between two meshes dynamically. Unity doesn't have a built-in feature for OBJ morphing, so you'll need to:

1. Load two OBJ files into Mesh objects.
2. Ensure both meshes have the same vertex count and order.
3. Interpolate vertex positions between the two meshes over time.

Below is a Unity C# script to achieve this:

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[RequireComponent(typeof(MeshFilter))]
public class MorphOBJ : MonoBehaviour
{
    public Mesh meshA; // First mesh
    public Mesh meshB; // Second mesh (must have the same vertex count as meshA)
    public float morphDuration = 2f; // Duration of the morph in seconds

    private MeshFilter meshFilter;
    private Mesh morphedMesh;
    private float morphProgress = 0f;
    private bool isMorphing = false;

    void Start()
    {
        meshFilter = GetComponent<MeshFilter>();

        if (meshA == null || meshB == null)
        {
            Debug.LogError("Please assign both meshes in the inspector.");
            return;
        }

        if (meshA.vertexCount != meshB.vertexCount)
        {
            Debug.LogError("Meshes must have the same vertex count to morph.");
            return;
        }

        // Create a new mesh for the morphing process
        morphedMesh = new Mesh();
        meshFilter.mesh = morphedMesh;

        // Initialize the morphed mesh with the first mesh
        morphedMesh.vertices = meshA.vertices;
        morphedMesh.triangles = meshA.triangles;
        morphedMesh.normals = meshA.normals;
    }

    void Update()
    {
        if (isMorphing)
        {
            morphProgress += Time.deltaTime / morphDuration;

            if (morphProgress >= 1f)
            {
                morphProgress = 1f;
                isMorphing = false;
            }

            MorphMeshes(morphProgress);
        }

        // Example input to start morphing
        if (Input.GetKeyDown(KeyCode.Space))
        {
            StartMorph();
        }
    }

    public void StartMorph()
    {
        morphProgress = 0f;
        isMorphing = true;
    }

    private void MorphMeshes(float t)
    {
        Vector3[] verticesA = meshA.vertices;
        Vector3[] verticesB = meshB.vertices;
        Vector3[] morphedVertices = new Vector3[verticesA.Length];

        for (int i = 0; i < verticesA.Length; i++)
        {
            morphedVertices[i] = Vector3.Lerp(verticesA[i], verticesB[i], t);
        }

        morphedMesh.vertices = morphedVertices;
        morphedMesh.triangles = meshA.triangles; // Assuming the same topology
        morphedMesh.RecalculateNormals();
    }
}

Steps to Use the Script:

1. Prepare the Meshes:

• Import two OBJ files into Unity and create meshes from them.
• Ensure both OBJ files have the same number of vertices and topology (vertex order).

2. Assign Meshes:

• Attach the script to a GameObject with a MeshFilter.
• Assign meshA and meshB in the Unity Inspector with the meshes you want to morph between.

3. Trigger the Morph:

• Press the Space key to start the morph animation.
• Adjust the morphDuration to control the speed.

This script smoothly interpolates vertex positions from one mesh to another over time, creating a morphing effect. If your OBJ files do not have matching vertex counts or order, consider preprocessing them in 3D modeling software to ensure compatibility.