SPherecammov

float map(vec3 pos)
{
    vec3 q = pos;

	float d = length(pos) - 0.25;
    float d2 = pos.y - (-0.25);

    return min(d, d2);
}

float castRay(vec3 ro, vec3 rd)
{
    float t = 0.0;
    for(int i = 0; i < 100; i++)
    {
    	vec3 pos = ro + t * rd;

        float h = map(pos);
        if(h < 0.001)
        {
        	break;
        }
        t += h;

        if(t > 20.0) break;

    }

    if(t > 20.0) t = -1.0;

    return t;
}

vec3 calcNormal(vec3 pos)
{
    vec2 e = vec2(0.0001, 0.0);

	return normalize(vec3(
        					map(pos+e.xyy) - map(pos-e.xyy),
        					map(pos+e.yxy) - map(pos-e.yxy),
        					map(pos+e.yyx) - map(pos-e.yyx)
    				));
}

void mainImage( out vec4 fragColor, in vec2 fragCoord )
{
    // Normalized pixel coordinates (from 0 to 1)
    vec2 p = (2.0 * fragCoord- iResolution.xy) / iResolution.y;

	/*
vec3 ro = vec3(0.0,0.0,1.0);
   vec3 rd = normalize(vec3(p, -1.5));
	*/

	vec3 col = vec3(0.0);


    // Camera Look at

    float an = iTime;
    vec3 ro = vec3(1. * sin(an), 0.0, 1.0 * cos(an));

	float cameraZoom = 2.5;
	vec3 target = vec3(0.1, 0., 0.);

	vec3 ww = normalize(target - ro);
	vec3 uu = normalize(cross(ww, vec3(0.,1.,0.)));
	vec3 vv = normalize(cross(uu, ww));

	vec3 rd = normalize(p.x * uu + p.y * vv + cameraZoom * ww);

    // Rendering part
	float t = castRay(ro, rd);


    if(t > 0.)
    {

        vec3 pos = ro + t * rd;
        vec3 nor = calcNormal(pos);
       	vec3 sundir = normalize(vec3(0.8, 0.4, 0.2));


        float sundif = clamp(dot(nor, sundir), 0.0, 1.0);

        float sun_sha = smoothstep(castRay(pos + nor * 0.001, sundir), 0.0, 1.0);
        float sky_dif = clamp(dot(nor,vec3(0.0,1.0,0.0)), 0.0, 1.0);;

        col = vec3(1.0, 0.7, 0.5) * sundif * sun_sha;
        col += vec3(0.0, 0.2, 0.4) * sky_dif;
    }
    // Output to screen
    fragColor = vec4(col,1.0);
}