How (update,set, apply) dynamically color on a model of a XNA project?

Question

I encounter a problem for set a background color on my model instantiated. I can change the texture but not change color. Is there a parameter for change the color ? Or change the opacity ? I am looking for a way to highlight a model.

thank you so much

Here is my code used: Everything works except the two last line. I searched but can not find name parameter for color and opacity

//Does not work

effect.Parameters["Color"].SetValue(new Vector3(0,1,0)); effect.Parameters["Opacity"].SetValue(0.5f);

        void DrawModelHardwareInstancing(Model model, Matrix[] modelBones,
                                             Matrix[] instances, Matrix view, Matrix projection)
            {
                 .......


                foreach (ModelMesh mesh in model.Meshes)
                {
                    foreach (ModelMeshPart meshPart in mesh.MeshParts)
                    {
                        // Tell the GPU to read from both the model vertex buffer plus our instanceVertexBuffer.
                        Game.GraphicsDevice.SetVertexBuffers(
                            new VertexBufferBinding(meshPart.VertexBuffer, meshPart.VertexOffset, 0),
                            new VertexBufferBinding(instanceVertexBuffer, 0, 1)
                        );

                        Game.GraphicsDevice.Indices = meshPart.IndexBuffer;


                        // Set up the instance rendering effect.
                        Effect effect = meshPart.Effect;
                        //effect.CurrentTechnique = effect.Techniques["HardwareInstancing"];
                        effect.Parameters["World"].SetValue(modelBones[mesh.ParentBone.Index]);

                        //Work perfect
                        effect.Parameters["View"].SetValue(view);
                        effect.Parameters["Projection"].SetValue(projection);
                        effect.Parameters["Texture"].SetValue(textureInstancedModel);
                        /* ***************************** */
                        //Does not work
                        effect.Parameters["Color"].SetValue(new Vector3(0,1,0));
                        effect.Parameters["Opacity"].SetValue(0.5f);
                        /* ***************************** */

                        // Draw all the instance copies in a single call.
                        foreach (EffectPass pass in effect.CurrentTechnique.Passes)
                        {
                            pass.Apply();

                            Game.GraphicsDevice.DrawInstancedPrimitives(PrimitiveType.TriangleList, 0, 0,
                                                                   meshPart.NumVertices, meshPart.StartIndex,
                                                                   meshPart.PrimitiveCount, instances.Length);
                        }
                    }
               ........
}

Answer 1

Changing color to a texture with an effect file can be done in this way:

HLSL CODE

And then a simple test game:

VertexBuffer bufferVertex;
IndexBuffer bufferIndex;
Effect effect;
Matrix View, Projection;

protected override void LoadContent()
{

    effect = Content.Load<Effect>("Color");
    Projection = Matrix.CreateOrthographic(graphics.PreferredBackBufferWidth, graphics.PreferredBackBufferHeight, -10000f, 10000f);

    View =
    Matrix.CreateScale(1.0f) *
    Matrix.CreateRotationY(MathHelper.ToRadians(225)) *
    Matrix.CreateRotationX(MathHelper.ToRadians(30)) *
    Matrix.CreateTranslation(0, 0, 0);

    VertexPositionTexture[] vertices = new VertexPositionTexture[4];

    vertices[0] = new VertexPositionTexture(new Vector3(-128, 0, -128), new Vector2(0, 1));
    vertices[1] = new VertexPositionTexture(new Vector3(128, 0, -128), new Vector2(1, 1));
    vertices[2] = new VertexPositionTexture(new Vector3(-128, 0, 128), new Vector2(0, 0));
    vertices[3] = new VertexPositionTexture(new Vector3(128, 0, 128), new Vector2(1, 0));

    bufferVertex = new VertexBuffer(GraphicsDevice, VertexPositionTexture.VertexDeclaration, 4, BufferUsage.WriteOnly);
    bufferVertex.SetData(vertices);

    int[] indexs = new int[6] { 0, 1, 2, 2, 1, 3 };

    bufferIndex = new IndexBuffer(GraphicsDevice, IndexElementSize.ThirtyTwoBits, 6, BufferUsage.WriteOnly);
    bufferIndex.SetData(indexs);
}

Drawing

protected override void Draw(GameTime gameTime)
{
    GraphicsDevice.Clear(Color.CornflowerBlue);

    effect.CurrentTechnique = effect.Techniques["Color"];
    effect.Parameters["Projection"].SetValue(Projection);
    effect.Parameters["View"].SetValue(View);
    effect.Parameters["World"].SetValue(Matrix.Identity);

    effect.Parameters["xTexture"].SetValue(Content.Load<Texture2D>("grass"));
    effect.Parameters["xAmbient"].SetValue(new Color(255, 255, 255).ToVector4());
    effect.Parameters["xColor"].SetValue(Color.Black.ToVector4());

    foreach (EffectPass pass in effect.CurrentTechnique.Passes)
    {
        pass.Apply();
    }


    GraphicsDevice.Indices = bufferIndex;
    GraphicsDevice.SetVertexBuffer(bufferVertex);
    GraphicsDevice.DrawIndexedPrimitives(PrimitiveType.TriangleList, 0, 0, 4, 0, 2);

    base.Draw(gameTime);
}

Example Default:

effect.Parameters["xAmbient"].SetValue(new Color(255, 255, 255).ToVector4());
effect.Parameters["xColor"].SetValue(new Color(0, 0, 0).ToVector4());

Example Red:

effect.Parameters["xAmbient"].SetValue(new Color(255, 0, 0, 0).ToVector4());
effect.Parameters["xColor"].SetValue(new Color(255, 0, 0, 0).ToVector4());

Hope that this can be applied anywhere else.

Answer 2

This is not really dynamically coloring but you can alter the lighting effects to achieve the same thing. The AmbientLightColor effect should work.

effect.AmbientLightColor = new Color(r, b, g);

Also there is an effect.alpha that you use for transparency iirc which takes a float between 0-1.