For a cel shader I wrote, the edge detection only works with a 2D texture/rendertarget. So, I adapted the render methods so it draws the texture to the rendertarget, which is set to a texture and drawn with SpriteBatch.
Except, the SpriteBatch (seems?) to be ignoring my settings for it:
spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.Opaque, SamplerState.LinearWrap, DepthStencilState.Default, RasterizerState.CullNone);
Would obviously draw the objects correctly. However, it doesn't.