XNA pixel shader clamping error - xna

Question

I want to apply a pixel shader onto my background sprite, to create some sort of lighting.
So i draw a Render Target with the light on it and want to merge it onto the background via the Pixel shader.
This is the essential code:
GraphicsDevice.Clear(Color.Black);
spriteBatch.Begin(SpriteSortMode.Immediate, BlendState.AlphaBlend);
lighting.Parameters["lightMask"].SetValue(lightingMask);
lighting.CurrentTechnique.Passes[0].Apply();
spriteBatch.Draw(hexBack, new Vector2(0, 0), Color.White);
spriteBatch.End();
In this case, hexBack is the Rendertarget with a simple sprite drawn in it and lightingMask is the rendertarget with the light texture in it.
Both are Backbuffer width and height.
So when i try to run the program, it crashes with:
XNA Framework Reach profile requires TextureAddressMode to be Clamp when using texture sizes that are not powers of two.
So i tried to set up clamping, but i cant find a way to get it working.
The shader code:
texture lightMask;
sampler mainSampler : register(s0);
sampler lightSampler = sampler_state{Texture = lightMask;};
struct PixelShaderInput
{
float4 TextureCoords: TEXCOORD0;
};
float4 PixelShaderFunction(PixelShaderInput input) : COLOR0
{
float2 texCoord = input.TextureCoords;
float4 mainColor = tex2D(mainSampler, texCoord);
float4 lightColor = tex2D(lightSampler, texCoord);
return mainColor * lightColor;
}
technique Technique1
{
pass Pass1
{
PixelShader = compile ps_2_0 PixelShaderFunction();
}
}
Thanks for your help!
pcnx

Answer 1

If you are unable to use power of two textures, you have to change your Spritebath.begin call and specify a SamplerState. The minimum to specify should be
public void Begin (
SpriteSortMode sortMode,
BlendState blendState,
SamplerState samplerState,
DepthStencilState depthStencilState,
RasterizerState rasterizerState
)

Answer 2

The error refers to your texture addressing mode (ie: does the texture wrap around at the edges, or is it clamped at the edges). Nothing to do with a shader.
Use one of the overloads for SpriteBatch.Begin (MSDN) that takes a SamplerState, and pass in SamplerState.LinearClamp (MSDN).
The default for SpriteBatch.Begin is SamplerState.LinearClamp, so you must be setting a different state (eg: LinearWrap) onto the graphics device somewhere else in your code? Don't do that.
(Alternately: change from the Reach profile to the HiDef profile in your project settings.)