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// A GLSL vertex program for handling 1 directional light with specular.
// This implements per-vertex lighting (Gouraud shading).

// GL2ES2: Java3D built-in attributes, these are calculated and passsed in if declared here
attribute vec4 glVertex;
attribute vec3 glNormal;  

// GL2ES2: Java3D built-in uniforms, these are calculated and passsed in if declared here
uniform mat4 glModelViewMatrix;
uniform mat4 glModelViewProjectionMatrix;
uniform mat3 glNormalMatrix;

 

uniform vec4 glLightModelambient;

struct material
{
	int lightEnabled;
 	vec4 ambient;
 	vec4 diffuse;
 	vec4 emission;// note vec4 extra 1.0 sent through for ease
 	vec3 specular;
 	float shininess;
};
uniform material glFrontMaterial;

struct lightSource
{
	 vec4 position;
	 vec4 diffuse;
	 vec4 specular;
	 float constantAttenuation, linearAttenuation, quadraticAttenuation;
	 float spotCutoff, spotExponent;
	 vec3 spotDirection;
};

uniform int numberOfLights;
const int maxLights = 1;
uniform lightSource glLightSource[maxLights];

//GL2ES2: varying color data needs to be defined
varying vec4 glFrontColor;
varying vec4 glFrontSecondaryColor;

void directionalLight0(
    in    vec3 normal,
    inout vec4 ambient,
    inout vec4 diffuse,
    inout vec3 specular)
{
    // Normalized light direction and half vector
    vec3 lightDirection = normalize(vec3(glLightSource[0].position));
   
    //GL2ES2: half vector must be calculated
    //vec3 halfVector = normalize(vec3(gl_LightSource[0].halfVector));
    //http://stackoverflow.com/questions/3744038/what-is-half-vector-in-modern-glsl
    vec3 ecPos = vec3(glModelViewMatrix * glVertex);	
    vec3 ecL;
    if(	glLightSource[0].position.w == 0.0)
    	ecL = vec3(glLightSource[0].position.xyz);// no -ecPos in case of dir lights?
  	else
		ecL = vec3(glLightSource[0].position.xyz - ecPos);
    vec3 L = normalize(ecL.xyz);
 	vec3 V = -ecPos.xyz; 
 	vec3 halfVector = normalize(L + V);

    float nDotVP; // normal . light_direction
    float nDotHV; // normal . light_half_vector
    float pf; // power factor

    nDotVP = max(0.0, dot(normal, lightDirection));
    nDotHV = max(0.0, dot(normal, halfVector));

    if (nDotVP == 0.0) {
	pf = 0.0;
    }
    else {
	pf = pow(nDotHV, glFrontMaterial.shininess);
    }

    ambient += glLightModelambient;
    diffuse += glLightSource[0].diffuse * nDotVP;
    specular += glFrontMaterial.specular * pf;
}


void main()
{
    vec3 tnorm = normalize(vec3(glNormalMatrix * glNormal));
    vec4 amb = vec4(0.0);
    vec4 diff = vec4(0.0);
    vec3 spec = vec3(0.0);
    int i;

    // Transform the vertex
    vec4 outPosition = glModelViewProjectionMatrix * glVertex;

    directionalLight0(tnorm, amb, diff, spec);
    
    //GL2ES2: sceneColor Derived. Ecm + Acm * Acs (Acs is normal glLightModelambient)
 	vec4 sceneColor = glFrontMaterial.emission + glFrontMaterial.ambient * glLightModelambient;

    // Apply the result of the lighting equation
    vec4 outSecondaryColor = vec4(vec3(spec * glFrontMaterial.specular), 1.0);
    vec4 outColor = vec4(vec3( sceneColor +
		       amb * glFrontMaterial.ambient +
		       diff * glFrontMaterial.diffuse), 1.0);

    glFrontColor = outColor;
    glFrontSecondaryColor = outSecondaryColor;
    gl_Position = outPosition;
}