I've been implementing a lighting system in XNA using shaders I didn't write myself, and I've run into an issue: the system works perfectly if the dimensions of the game are powers of two (right now it's running at 1024x512), but will otherwise break down at the line GraphicsDevice.DrawUserPrimitives(PrimitiveType.TriangleStrip, Vertices, 0, 2);, throwing an exception which states that "XNA Framework Reach profile requires TextureAddressMode to be Clamp when using texture sizes that are not powers of two."
In a search of the internet, the most common solution is to put the line GraphicsDevice.SamplerStates[0] = SamplerState.LinearClamp directly above the line above. I've tried this, and it has had no effect. In fact, during my attempts to tease out a solution, it seemed to be that GraphicsDevice.SamplerStates[0] was null before I set it with that line, leading me to believe that this problem could also perhaps be solved by selecting that as the active sampler state--although I'm also not sure how to do that.
Otherwise, based on other information I've found, I believe that I need to set the TextureAddressMode from within the shader. I was directed to this page for information on how to do so, but I confess to still being baffled--I've never used HLSL before, and I'm unsure of how to use the information on that page.
If there's any more information I need to provide, I'd be more than happy to do so, and I first asked a question which led me towards my present one here.
In your HLSL look for the line that declares the sampler that the pixel shader is using.
You can set the address mode to clamp in this line.
SamplerState somethingLikeThis {
Filter = MIN_MAG_MIP_LINEAR;
AddressU = Clamp;
AddressV = Clamp;
};