Render error in xna DrawPrimitive for Assimp Mesh

Question

I am trying to render the vertices of a scene with a cube I exported as an OBJ from Blender. The 8 vertices become 24 when imported into XNA but when I render it I dont see all faces. This is not an issue of missing meshes because I'm pretty sure this is being stored as the first and only mesh. I suspect this is because of the vectors defined in the Assimp Mesh object but I can't seem to find any help for this.

THIS IS SOLVED! The code shows how to render a 3D model using only Assimp and XNA with vertex and index buffers. oScene is the Scene object imported using Assimp. This code only draws faces in a single color without textures.

Here is the relevant code:

   private void SetUpVertices()
    {
        mMesh = oScene.Meshes[0];
        vertices = new VertexPositionColor[mMesh.VertexCount];
        indices = new  short[mMesh.FaceCount*3];

        int i=0;
        foreach (Vector3D mVec in mMesh.Vertices)
        {
            vertices[i] = new VertexPositionColor(new Vector3(mVec.X, mVec.Y, mVec.Z), Color.Red);
            i++;
        }

        int f = 0;
        Face mFace;
        for (i = 0 ; i < mMesh.FaceCount*3 ; i=i+3) 
        {
            mFace = mMesh.Faces[f];
            f++;
            indices[i] = (short)mFace.Indices[0];
            indices[i + 1] = (short)mFace.Indices[1];
            indices[i + 2] = (short)mFace.Indices[2];

        }

        vertexBuffer = new VertexBuffer(device, VertexPositionColor.VertexDeclaration, vertices.Length, BufferUsage.WriteOnly);
        vertexBuffer.SetData(vertices);

        indexBuffer = new IndexBuffer(device, typeof(short), indices.Length, BufferUsage.None);
        indexBuffer.SetData(indices);

    }

    private void SetUpCamera()
    {
        cameraPos = new Vector3(0, 5, 9);
        viewMatrix = Matrix.CreateLookAt(cameraPos, new Vector3(0, 0, 1), new Vector3(0, 1, 0));
        projectionMatrix = Matrix.CreatePerspectiveFieldOfView(MathHelper.PiOver4, device.Viewport.AspectRatio, 1.0f, 200.0f);
    }

    protected override void Draw(GameTime gameTime)
    {
        device.Clear(ClearOptions.Target | ClearOptions.DepthBuffer, Color.DarkSlateBlue, 1.0f, 0);
        effect = new BasicEffect(GraphicsDevice);
        effect.VertexColorEnabled = true;

        effect.View = viewMatrix;
        effect.Projection = projectionMatrix;
        effect.World = Matrix.Identity;

        foreach (EffectPass pass in effect.CurrentTechnique.Passes)
        {
            pass.Apply();
            device.SetVertexBuffer(vertexBuffer);
            device.Indices = indexBuffer;
            device.DrawIndexedPrimitives(Microsoft.Xna.Framework.Graphics.PrimitiveType.TriangleList, 0, 0, oScene.Meshes[0].VertexCount, 0, mMesh.FaceCount);
        }

        base.Draw(gameTime);
    }

Answer 1

device.DrawPrimitives(Microsoft.Xna.Framework.Graphics.PrimitiveType.TriangleStrip, 0, oScene.Mesh[0].VertexCount);

I believe the problem may be that you are using TriangleStrip instead of TriangleList. It also primarily seems to be the draw call as well (based on my own quick test using your draw call). Try this:

device.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, oScene.Mesh[0].VertexCount, 0, triangleCount);

You'll have to set triangleCountfrom the oScene.Mesh[0] object (don't know what it is in Assimp, sorry). I'm currently using a draw call like this, and .OBJ files loaded from my own .OBJ importer work fine.