#extension GL_OES_standard_derivatives : enable

precision highp float;

uniform float time;
uniform vec2 mouse;
uniform vec2 resolution;

#define PI 3.1415926535897932384626433832795


vec3 shade1(float r, vec2 center, vec2 pos, vec3 lights[2])
{
    return vec3(255,0,0);
}

vec3 shade2(float r, vec2 center, vec2 pos, vec3 lights[2])
{
    float dist = sqrt(pos.x*pos.x + pos.y*pos.y);
    if (dist < r)
	return vec3(1,0,0);
    else
	return vec3(0,0,0);
}

vec3 shade3(float r, vec2 center, vec2 pos, vec3 lights[2])
{
    float z = sqrt(r * r - pos.x * pos.x - pos.y * pos.y);  // z coordinate of the fragment (given x, y)
    if (z < r)
	return vec3(z/r,0,0);
    else
	return vec3(0,0,0);
}

vec3 shade4(float r, vec2 center, vec2 pos, vec3 lights[2])
{
    float z = sqrt(r * r - pos.x * pos.x - pos.y * pos.y);  // z coordinate of the fragment (given x, y)
    vec3 n = normalize(vec3(pos.x, pos.y, z));  // surface normal
    float val = acos(dot(n, vec3(0,0,1)));
    return vec3(val,val,0);
}

vec3 shade5(float r, vec2 center, vec2 pos, vec3 lights[2])
{
    float z = sqrt(r * r - pos.x * pos.x - pos.y * pos.y);  // z coordinate of the fragment (given x, y)
    vec3 n = normalize(vec3(pos.x, pos.y, z));  // surface normal

    float val0 = max(dot(n, lights[0]), 0.0);
    vec3 c0 = vec3(val0, val0, val0);
	
    float val1 = max(dot(n, lights[1]), 0.0);
    vec3 c1 = vec3(val1, val1, val1);
    return c0+c1;
}

vec3 shade6(float r, vec2 center, vec2 pos, vec3 lights[2])
{
    float z = sqrt(r * r - pos.x * pos.x - pos.y * pos.y);  // z coordinate of the fragment (given x, y)
    vec3 n = normalize(vec3(pos.x, pos.y, z));  // surface normal

    float val0 = max(dot(n, lights[0]), 0.0);
    vec3 c0 = vec3(val0, val0, 0.0);
	
    float val1 = max(dot(n, lights[1]), 0.0);
    vec3 c1 = vec3(0.0, val1, val1);
	
	
    float dist = sqrt(pos.x*pos.x + pos.y*pos.y);

    float mod1 = 0.5*sin(lights[0].x*4.0*dist/r*PI);
    float mod2 = 0.5*cos(4.0*dist/r*PI+PI*0.5);
	
    return mod1*c0+mod2*c1;
}

void main( void )
{
    // sphere definition:
    vec2 center = resolution.xy / 2.0;  // center of screen as the center of the sphere; iResolution: viewport resolution (in pixels)
    float r = resolution.y / 3.0;  // r: radius of the sphere
    // fragCoord: screen space coordinates (based on the viewport), see https://computergraphics.stackexchange.com/questions/5724/glsl-can-someone-explain-why-gl-fragcoord-xy-screensize-is-performed-and-for
    vec2 pos = gl_FragCoord.xy - center;

    // light vector:
    vec3 lights[2];  // two lights
	
    // the lights will move over time; the positions of the lights:
    lights[0] = normalize(vec3(sin(time), sin(time), cos(time)));
    lights[1] = normalize(vec3(-sin(time), cos(time), sin(time)));

    vec3 c = shade6(r, center, pos, lights);  // calculate the color for each fragment

    gl_FragColor = vec4(c, 1.0);
}