//
// File: Maya_EnvironmentMap.cgh
//
// Description : Include file for Maya environment mapping functions
//

// Lookup enumeration
#define kEnvironmentNone	0
#define kEnvironmentSphere	1
#define kEnvironmentCube	2
#define kEyeSpaceEnvSphere	3
#define k3DEnviroment		4
#define kHWEnvCube			5


float4 MAYA_environmentLookup(float3 lookupVector,
							  sampler lookupTexture,
							  int environmentType )
{
	float4 lookupColor;
	
	if (environmentType == kEnvironmentCube)
	{
#if defined(IS_THIS_CORRECT)
		// this doubles the instructions. 
		float3 axis = abs(lookupVector);

		if (axis.x >= axis.y && axis.x >= axis.z) {
			lookupVector.y *= -1.0;
			lookupVector.z *= -1.0;
		}
		else if (axis.z >= axis.y) {
			lookupVector.x *= -1.0;
			lookupVector.y *= -1.0;
		}		
#endif	
		lookupColor = texCUBE(lookupTexture, lookupVector);  
	}
	else if (environmentType == kHWEnvCube) 
	{
		lookupColor = texCUBE(lookupTexture, lookupVector);  
	}	
	else if (environmentType == kEnvironmentSphere)
	{
		// This calculation is directly taken from the OpenGL spec's sphere
		// mapping section.
		//
		float x = lookupVector.x;
		float y = lookupVector.y;
		float z = lookupVector.z + 1;
		float m = 2.0 * sqrt(x * x + y * y + z * z);

		float2 sphereUv = lookupVector.xy / m + 0.5;
	
		lookupColor = tex2D(lookupTexture, float3(sphereUv, 1.0));
	}
	else if (environmentType == kEyeSpaceEnvSphere)
	{
		// This from is from the Orange book
		float2 sphereUv;
		float3 Xunitvec = float3( 1.0, 0.0, 0.0 );
		float3 Yunitvec = float3( 0.0, 1.0, 0.0 );
		sphereUv.y = dot(lookupVector, Yunitvec );
		lookupVector.y = 0.0;
		sphereUv.x = dot(lookupVector, Xunitvec ) * 0.5;
		
		if (lookupVector.z >= 0.0) {
			sphereUv = (sphereUv+1.0) * 0.5;
		}
		else
		{
			sphereUv.y = (sphereUv.y + 1.0) * 0.5;
			sphereUv.x = (-sphereUv.x) * 0.5 + 1.0;
		}
		
		lookupColor = tex2D(lookupTexture, float3(sphereUv, 1.0));	
	}
	else if (environmentType == k3DEnviroment)
	{		
		lookupColor = tex3D(lookupTexture, lookupVector.xyy);
	}
	else 
	{
		lookupColor = tex2D(lookupTexture, lookupVector.xy);
	}
		
	return lookupColor;
}