
uniform sampler3D volumeTexture;
uniform sampler3D volumeTexture2;
uniform sampler2D RGBlookupTexture;
uniform sampler2D RAGABAlookupTexture;

uniform int channel;

uniform float silhCont;
uniform float silhExp;

varying vec3 V;
varying vec3 V1;
varying vec3 L;

vec3 eval_normal(void)
{
	vec3 normal;
	//==============================================
	//EVALUATE OUR NORMAL BY CENTRAL DIFFERENCE
	//==============================================
	float stepsize	= 1.0/256.0;
	vec3 sample1,sample2,sample3,sample4;
	sample1.x = texture3D(volumeTexture, gl_TexCoord[0].stp-vec3(stepsize,0,0)).x;
	sample2.x = texture3D(volumeTexture, gl_TexCoord[0].stp+vec3(stepsize,0,0)).x;
	sample1.y = texture3D(volumeTexture, gl_TexCoord[0].stp-vec3(0,stepsize,0)).x;
	sample2.y = texture3D(volumeTexture, gl_TexCoord[0].stp+vec3(0,stepsize,0)).x;
	sample1.z = texture3D(volumeTexture, gl_TexCoord[0].stp-vec3(0,0,stepsize)).x;
	sample2.z = texture3D(volumeTexture, gl_TexCoord[0].stp+vec3(0,0,stepsize)).x;

	normal = sample2-sample1;
	normal = normalize(normal);
	return normal;
}

void main()
{	
	//get the texture rgb data
	float texValue = texture3D(volumeTexture, gl_TexCoord[0].stp).x;
	//if(texValue==0.0) discard;

	//==============================
	//APLY OUR TRANSFER FUNCTION
	//==============================
	//make sure we sample from centre of lookup table
	//float lookup_offset = (1.0/256.0/2.0);
	//texValue += lookup_offset;

	//get lookup table values
	//r,g,b,ra,ga,ba
	vec3 RGBlookupValue, RAGABAlookupValue;
	RGBlookupValue = RAGABAlookupValue = vec3(0.0);
	vec4 finalColour = vec4(0.0);

	if(channel==0)
	{
		RGBlookupValue.x = texture2D(RGBlookupTexture, vec2(texValue, 0.0)).x;
		RAGABAlookupValue.x = texture2D(RAGABAlookupTexture, vec2(texValue, 0.0)).x;

		if(RAGABAlookupValue.x == 0.0) discard;

		finalColour = vec4(RGBlookupValue.x,0.0,0.0, RAGABAlookupValue.x);
	}
	else if(channel==1)
	{
		RGBlookupValue.y = texture2D(RGBlookupTexture, vec2(texValue, 0.0)).y;
		RAGABAlookupValue.y = texture2D(RAGABAlookupTexture, vec2(texValue, 0.0)).y;

		if(RAGABAlookupValue.y == 0.0) discard;

		finalColour = vec4(0.0,RGBlookupValue.y,0.0, RAGABAlookupValue.y);
	}
	else if(channel==2)
	{
		RGBlookupValue.z = texture2D(RGBlookupTexture, vec2(texValue, 0.0)).z;
		RAGABAlookupValue.z = texture2D(RAGABAlookupTexture, vec2(texValue, 0.0)).z;

		if(RAGABAlookupValue.z == 0.0) discard;

		finalColour = vec4(0.0,0.0,RGBlookupValue.z, RAGABAlookupValue.z);
	}
	else if(channel==3)
	{
		RGBlookupValue.x = texture2D(RGBlookupTexture, vec2(texValue, 0.0)).x;
		RAGABAlookupValue.x = texture2D(RAGABAlookupTexture, vec2(texValue, 0.0)).x;
		
		if(RAGABAlookupValue.x == 0.0) discard;
		
		finalColour = vec4(RGBlookupValue.x,RGBlookupValue.x,RGBlookupValue.x, RAGABAlookupValue.x);
	}
	else if(channel==4)
	{
		float texValue2 = texture3D(volumeTexture2, gl_TexCoord[0].stp).x;
		
		RGBlookupValue.x = texture2D(RGBlookupTexture, vec2(texValue, 0.5)).x;
		RAGABAlookupValue.x = texture2D(RAGABAlookupTexture, vec2(texValue2, 0.5)).x;

		if(RAGABAlookupValue.x == 0.0) discard;

		finalColour = vec4(RGBlookupValue.x,RGBlookupValue.x,RGBlookupValue.x, RAGABAlookupValue.x);	
	}
	
	vec3 N = eval_normal();

	float dotView = dot(N, L);
	
	vec4 silhouette = vec4(0.0);
	finalColour.xyz *=  silhCont*pow(1.0-abs(dotView),silhExp);
	
	//assing the colour to our final colour
	gl_FragColor = finalColour;
}
