tex3d.hlsl

static float k_lut_size = 1.0 / 16.0;
static float k_lut_pixel_size = k_lut_size / 16.0;
static float k_lut_half_pixel_size = k_lut_pixel_size / 2.0f;

float4 tex3D(sampler2D tex, float3 coord)
{
	// Clamp the sample to within one 16x16 slice to avoid filtering bleed.
	float y = coord.y;
	y = max(y - k_lut_half_pixel_size, k_lut_half_pixel_size);

	// Offset to the right depth slice now.	
	y += (coord.z - fmod(coord.z,  k_lut_size)) * k_lut_size;
	
	// We skip filtering between slices for performance.
	return tex2D(tex, float2(coord.x, y));
}