Transparent textures with MDX

This is just a quick, late night writeup on how to draw transparent textures onto the screen using Managed DirectX.

Firstly, we load the texture in an initilisation routine:

public void Initialize()
{
   tex = TextureLoader.FromFile(Form1.Device, ".\\test.png");
    rect = new Rectangle(50, 50, 40, 40); // assuming our png is 40x40
}

Then we render the texture onto a 2-triangle trianglefan:

public void Render()
{
  // device has been cleared and beginscene has been called

    CustomVertex.TransformedTextured[] screenVertices =
        new CustomVertex.TransformedTextured[4];
    screenVertices[0] = new CustomVertex.TransformedTextured(
        rect.X, rect.Y, 1.0f, 1.0f, 0.0f, 0.0f);
    screenVertices[1] = new CustomVertex.TransformedTextured(
        rect.X + rect.Width, rect.Y, 1.0f, 1.0f, 1.0f, 0.0f);
    screenVertices[2] = new CustomVertex.TransformedTextured(
        rect.X + rect.Width, rect.Y + rect.Height, 1.0f, 1.0f, 1.0f, 1.0f);
    screenVertices[3] = new CustomVertex.TransformedTextured(
        rect.X, rect.Y + rect.Height, 1.0f, 1.0f, 0.0f, 1.0f);

    Form1.Device.RenderState.SourceBlend = Blend.SourceAlpha;
    Form1.Device.RenderState.DestinationBlend = Blend.InvSourceAlpha;
    Form1.Device.SetRenderState(RenderStates.AlphaBlendEnable, true);
    Form1.Device.SetTexture(0, tex);
    Form1.Device.VertexFormat = CustomVertex.TransformedTextured.Format;
    Form1.Device.DrawUserPrimitives(PrimitiveType.TriangleFan, 2, screenVertices);

    // endscene and present will be called by main render loop
}

The important things to notice are:

1. RenderState.SourceBlend = Blend.SourceAlpha
2. RenderState.DestinationBlend = Blend.InvSourceAlpha
3. SetRenderState(RenderStates.AlphaBlendEnable, true)

This is what the final product looks like: