title: Issue with alpha in 2d lighting shader in XNA 4.0
body: <p>I'm currently learning HLSL with XNA, I figured the best place to start after tutorials would be some simple 2D shaders. I'm attempting to implement a simple lighting shader in 2D.</p>
  
  <p>I draw the scene without shadows to a rendertarget, swap my rendertarget to a shadowmap, draw my light(each individually) onto the shadowmap via alpha channel, swap my rendertarget back to default and render the scene then the shadows on top.</p>
  
  <p>The alpha of the light changes depending on the distance of the current pixel and the point of the light, this is all working fine for me except when I render the scene, if two lights overlap it causes a nasty blending issue.</p>
  
  <p><img src="https://i.stack.imgur.com/Qx37P.png" alt="the problem"></p>
  
  <p>I'm using alphablend when I draw on the shadowmap, and when I draw the shadowmap to the scene.
  Am I just using the wrong blending settings here? I don't know much about blendstates.</p>
  
  <p>Sorry if the question was vague.</p>