/*
Copyright (c) 2019 The Khronos Group Inc.
Use of this source code is governed by an MIT-style license that can be
found in the LICENSE.txt file.
*/


attribute vec4 gtf_Color;
attribute vec4 gtf_Vertex;
attribute vec3 gtf_Normal;
attribute vec4 gtf_MultiTexCoord0;

uniform mat4 gtf_ModelViewProjectionMatrix;
uniform mat3 gtf_NormalMatrix;

varying vec4 gtf_TexCoord[1];
varying vec4 color;

vec4 Ambient;
vec4 Diffuse;
vec4 Specular;

const vec3 lightPosition = vec3(0.0, 0.0, 1.0);
const vec3 spotDirection = vec3(0.0, 0.0, -1.0);
const float spotCutoff = 180.0;
const float spotExponent = 0.0;

const float lightAttenuationConstant = 1.0;
const float lightAttenuationLinear = 0.0;
const float lightAttenuationQuadratic = 0.0;

const vec4 lightAmbient = vec4(0.0, 0.0, 0.0, 0.0);
vec4 lightDiffuse = vec4(1.0, 1.0, 1.0, 1.0);
vec4 lightSpecular = vec4(1.0, 1.0, 1.0, 1.0);

const float materialShininess = 0.0;

const vec4 sceneColor = vec4(0.0, 0.0, 0.0, 0.0);

void spotLight(in int i,
               in vec3 normal,
               in vec3 eye,
               in vec3 ecPosition3
               )
{
    float nDotVP;           // normal . light direction
    float nDotHV;           // normal . light half vector
    float pf;               // power factor
    float spotDot;          // cosine of angle between spotlight
    float spotAttenuation;  // spotlight attenuation factor
    float attenuation;      // computed attenuation factor
    float d;                // distance from surface to light source
    vec3 VP;                // direction from surface to light position
    vec3 halfVector;        // direction of maximum highlights

    // Compute vector from surface to light position
    VP = lightPosition - ecPosition3;

    // Compute distance between surface and light position
    d = length(VP);

    // Normalize the vector from surface to light position
    VP = normalize(VP);

    // Compute attenuation
    attenuation = 1.0 / (lightAttenuationConstant +
                         lightAttenuationLinear * d +
                         lightAttenuationQuadratic * d * d);

    // See if point on surface is inside cone of illumination
    spotDot = dot(-VP, normalize(spotDirection));

    if (spotDot < cos(radians(spotCutoff)))
        spotAttenuation = 0.0; // light adds no contribution
    else
        spotAttenuation = pow(spotDot, spotExponent);

    // Combine the spotlight and distance attenuation.
    attenuation *= spotAttenuation;

    halfVector = normalize(VP + eye);

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

    if (nDotVP == 0.0)
        pf = 0.0;
    else
        pf = pow(nDotHV, materialShininess);

    Ambient  += lightAmbient * attenuation;
    Diffuse  += lightDiffuse * nDotVP * attenuation;
    Specular += lightSpecular * pf * attenuation;
}

vec3 fnormal(void)
{
    //Compute the normal 
    vec3 normal = gtf_NormalMatrix * gtf_Normal;
    normal = normalize(normal);
    
	return normal;
}

void flight(in vec3 normal, in vec4 ecPosition, float alphaFade)
{
    vec3 ecPosition3;
    vec3 eye;

    ecPosition3 = (vec3 (ecPosition)) / ecPosition.w;
    eye = vec3 (0.0, 0.0, 1.0);

    // Clear the light intensity accumulators
    Ambient  = vec4 (0.0);
    Diffuse  = vec4 (0.0);
    Specular = vec4 (0.0);
   
   //lightSpecular = gtf_Color;

    spotLight(0, normal, eye, ecPosition3);

    color = sceneColor +
      Ambient  * gtf_Color +
      Diffuse  * gtf_Color;
    color += Specular * gtf_Color;
    color = clamp( color, 0.0, 1.0 );

    color.a *= alphaFade;
}

void main (void)
{
	vec3  transformedNormal;
    float alphaFade = 1.0;
	
	vec4 ecPosition = gtf_Vertex;
	
	color = gtf_Color;
	gtf_TexCoord[0] = gtf_MultiTexCoord0;
	gl_Position = gtf_ModelViewProjectionMatrix * gtf_Vertex;
	transformedNormal = fnormal();
    flight(transformedNormal, ecPosition, alphaFade);
}