title: XNA Alpha Blending to make part of a texture transparent
body: <p>What I am trying to do is use alpha blending in XNA to make part of a drawn texture transparent. So for instance, I clear the screen to some color, lets say Blue. Then I draw a texture that is red. Finally I draw a texture that is just a radial gradient from completely transparent in the center to completely black at the edge. What I want is the Red texture drawn earlier to be transparent in the same places as the radial gradient texture. So you should be able to see the blue back ground through the red texture.</p>
  
  <p>I thought that this would work.</p>
  
  <pre><code>GraphicsDevice.Clear(Color.CornflowerBlue);
  
  spriteBatch.Begin(SpriteBlendMode.None);
  spriteBatch.Draw(bg, new Vector2(0, 0), Color.White);
  spriteBatch.End();
  
  spriteBatch.Begin(SpriteBlendMode.None);
  
  GraphicsDevice.RenderState.AlphaBlendEnable = true;
  GraphicsDevice.RenderState.AlphaSourceBlend = Blend.One;
  GraphicsDevice.RenderState.AlphaDestinationBlend = Blend.Zero;
  GraphicsDevice.RenderState.SourceBlend = Blend.Zero;
  GraphicsDevice.RenderState.DestinationBlend = Blend.One;
  GraphicsDevice.RenderState.BlendFunction = BlendFunction.Add;
  
  spriteBatch.Draw(circle, new Vector2(0, 0), Color.White);
  spriteBatch.End();
  
  GraphicsDevice.RenderState.AlphaBlendEnable = false;
  </code></pre>
  
  <p>But it just seems to ignore all my RenderState settings. I also tried setting the SpriteBlendMode to AlphaBlend. It blends the textures, but that is not the effect I want.</p>
  
  <p>Any help would be appreciated.</p>