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

void directionalLight0(
    in    vec3 normal,
    inout vec4 ambient,
    inout vec4 diffuse,
    inout vec4 specular)
{
    // Normalized light direction and half vector
    vec3 lightDirection = normalize(vec3(gl_LightSource[0].position));
    vec3 halfVector = normalize(vec3(gl_LightSource[0].halfVector));

    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, gl_FrontMaterial.shininess);
    }

    ambient += gl_LightSource[0].ambient;
    diffuse += gl_LightSource[0].diffuse * nDotVP;
    specular += gl_LightSource[0].specular * pf;
}


// Per-pixel normal (input from vertex shader)
varying vec3  Normal;

void main()
{
    vec3 unitNorm = normalize(Normal);
    vec4 amb = vec4(0.0);
    vec4 diff = vec4(0.0);
    vec4 spec = vec4(0.0);
    int i;

    directionalLight0(unitNorm, amb, diff, spec);

    // Apply the result of the lighting equation
    vec4 secondaryColor = vec4(vec3(spec * gl_FrontMaterial.specular), 1.0);
    vec4 color = vec4(vec3(gl_FrontLightModelProduct.sceneColor +
		       amb * gl_FrontMaterial.ambient +
		       diff * gl_FrontMaterial.diffuse), 1.0);

    gl_FragColor = color + secondaryColor;
}