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// Algorithm from section 2.14.1 of OpenGL 2.1 specification.

attribute highp vec4 vertex;
attribute highp vec3 normal;
attribute highp vec4 texcoord;
uniform mediump mat4 matrix;
uniform mediump mat4 modelView;
uniform mediump mat3 normalMatrix;
varying highp vec4 qTexCoord;

uniform mediump vec4 scli;      // Specular intensity of the light
uniform mediump vec3 pli;       // Position of the light
uniform mediump float pliw;     // 0 for directional, 1 for positional.
uniform mediump vec4 acm;       // Ambient color of the material
uniform mediump vec4 dcm;       // Diffuse color of the material
uniform mediump vec4 scm;       // Specular color of the material
uniform mediump float srm;      // Specular exponent of the material
uniform mediump vec4 acs;       // Light model's ambient color of the scene
uniform bool viewerAtInfinity;  // Light model indicates viewer at infinity

varying mediump vec4 qColor;
varying mediump vec4 qSecondaryColor;

void qLightVertex(vec4 vertex, vec3 normal)
{
    int i, material;
    vec3 toEye, toLight, h;
    float angle, spot, attenuation;
    vec4 color, scolor;
    vec4 adcomponent, scomponent;

    // Start with the material's emissive color and the ambient scene color.
    // ecm is assumed to be black.
    color = acm * acs;
    scolor = vec4(0, 0, 0, 0);

    // Vector from the vertex to the eye position (i.e. the origin).
    if (viewerAtInfinity)
        toEye = vec3(0, 0, 1);
    else
        toEye = normalize(-vertex.xyz);

    // Determine the cosine of the angle between the normal and the
    // vector from the vertex to the light.
    if (pliw == 0.0)
        toLight = normalize(pli);
    else
        toLight = normalize(pli - vertex.xyz);
    angle = max(dot(normal, toLight), 0.0);

    // Calculate the ambient and diffuse light components.
    // Assumptions: acli = (0, 0, 0, 1), dcli = (1, 1, 1, 1).
    adcomponent = acm * vec4(0, 0, 0, 1) + angle * dcm;

    // Calculate the specular light components.
    if (angle != 0.0) {
        h = normalize(toLight + toEye);
        angle = max(dot(normal, h), 0.0);
        scomponent = pow(angle, srm) * scm; // scli = (1, 1, 1, 1).
    } else {
        scomponent = vec4(0, 0, 0, 0);
    }

    // Add up the color components we computed.
    color += adcomponent;
    scolor += scomponent;

    // Generate the final output colors.
    float alpha = dcm.a;
    qColor = vec4(clamp(color.rgb, 0.0, 1.0), alpha);
    qSecondaryColor = clamp(scolor, 0.0, 1.0);
}

void main(void)
{
    gl_Position = matrix * vertex;
    highp vec4 vertex = modelView * vertex;
    highp vec3 norm = normalize(normalMatrix * normal);
    qLightVertex(vertex, norm);
    qTexCoord = texcoord;
}