uniform float4x4 ViewProj;
uniform texture2d image;
uniform texture2d displacementMap;
uniform float2 texelScale;
uniform float2 displacementScale;

sampler_state textureSampler {
	Filter    = Trilinear;
	AddressU  = Wrap;
	AddressV  = Wrap;
};
sampler_state dispTextureSampler {
	Filter    = Trilinear;
	AddressU  = Clamp;
	AddressV  = Clamp;
};

struct VertDataIn {
	float4 pos : POSITION;
	float2 uv  : TEXCOORD0;
};

struct VertDataOut {
	float4 pos : POSITION;
	float2 uv  : TEXCOORD0;
};

VertDataOut VSDefault(VertDataIn v_in)
{
	VertDataOut vert_out;
	vert_out.pos = mul(float4(v_in.pos.xyz, 1.0), ViewProj);
	vert_out.uv  = v_in.uv;
	return vert_out;
}

float4 PSDisplace(VertDataOut v_in) : TARGET
{
	float2 disp = displacementMap.Sample(dispTextureSampler, v_in.uv).rg - float2(0.5, 0.5);

	// Handle 0..255 correctly (127, 128 are center)
	float2 signdisp = disp * float2(281474976710656.0, 281474976710656.0);
	float2 signs = float2(clamp(disp.r, -1.0, 1.0), clamp(disp.g, -1.0, 1.0));
	disp = (floor(abs(disp * 127.0)) / 127.0) * signs;

	float2 uv = v_in.uv + (disp * texelScale * displacementScale);
	float4 rgba = image.Sample(textureSampler, uv);

	return rgba;
}

technique Draw
{
	pass
	{
		vertex_shader = VSDefault(v_in);
		pixel_shader  = PSDisplace(v_in);
	}
}