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#define MAX_STEPS 100
#define MAX_DIST 100.
#define SURF_DIST .01






float GetDist(vec3 p)
{
	vec4 s = vec4(0,1,6,1);
    
    float sphereDist = length(p-s.xyz) - s.w;
    float planeDist = p.y;
    
    float d = min(sphereDist, planeDist);

    return d;
}

float RayMarch(vec3 ro, vec3 rd)
{
    
    float dO = 0.;
    
    for(int i = 0; i < MAX_STEPS; i++)
    {
    	vec3 p = ro + rd * dO;
        
        float dS = GetDist(p);
        dO += dS;
        
        if(dO > MAX_DIST || dS < SURF_DIST) break;
        
    }
    
    return dO;
}


vec3 GetNormal(vec3 p)
{

    float d = GetDist(p);
    vec2 e = vec2(.01, 0);
    vec3 n = d - vec3(
    	GetDist(p-e.xyy),
        GetDist(p-e.yxy),
        GetDist(p-e.yyx)
    );
    
    return normalize(n);
}

float GetLigth(vec3 p)
{
    
    vec3 lightPosition = vec3(0,5,6);
    lightPosition.xz += vec2(sin(iTime), cos(iTime)) * 2.;
    vec3 l = normalize(lightPosition-p);
    vec3 n = GetNormal(p);
    float dif = clamp(dot(n,l), 0.,1.0);
    
    float d = RayMarch(p + n * SURF_DIST * 2.,l);
    if(d < length(lightPosition-p)) dif *= .1;
    
    return dif;
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 uv = (fragCoord-.5 * iResolution.xy)/iResolution.y;

    // Time varying pixel color
    vec3 col = vec3(0.);
	
	vec3 ro = vec3(0,1,0);
    
    vec3 rd = normalize(vec3(uv.x, uv.y, 1));
	float d = RayMarch(ro,rd);
   
    vec3 p = ro + rd * d;
    
   	float dif = GetLigth(p);
    col = vec3(dif);
    
    
    
                 
               
    // Output to screen
    fragColor = vec4(col,1.0);
}