Blue Earth

fragment.c

#ifdef GL_ES
precision mediump float;
#endif

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

vec3 y_up = vec3( 0.0, 1.0, 0.0 );
vec3 eye_pos = vec3( 0.0, 0.0, -3.0 );
vec3 target_pos = vec3( 0.0, 0.0, 0.0 );
vec3 sphere_pos = vec3( 0.0 );

float sphere_rad = 1.0;
vec3 light_dir = vec3( 0.0, -1.0, 1.0 );

float sphere_distance( vec3 now_pos )
{
	return distance( sphere_pos, now_pos ) - sphere_rad;
}

float sphere_lambert( vec3 surface_pos )
{
	return clamp( dot( normalize(-light_dir), normalize(surface_pos - sphere_pos) ), 0.0, 1.0 );
}

void main( void )
{
	// Coord
	vec2 uv = 2.0 * ( gl_FragCoord.xy / resolution.xy )  - 1.0;
	uv.x *= resolution.x / resolution.y;
	
	// Camera
	eye_pos = 3.0 * vec3( cos(time), 0.0, sin(time) );
	vec3 eye_vec = normalize( target_pos - eye_pos );
	vec3 eye_left = normalize( cross( y_up, eye_vec ) );
	vec3 eye_up = normalize( cross( eye_vec, eye_left ) );
	
	// Raymarching
	vec3 ray_pos = eye_pos;
	vec3 ray_vec = normalize( eye_vec + uv.x * eye_left + uv.y * eye_up );
	float delta = 0.5;
	for ( int i = 0; i < 50; ++i )
	{
		float dist = sphere_distance( ray_pos );
		ray_pos += delta * dist * ray_vec;
	}
	
	// Color
	vec3 col = vec3( 0.0 );
	if ( sphere_distance( ray_pos ) < delta )
	{
		float lambert = sphere_lambert( ray_pos );
		vec3 blue = vec3( 0.0, 0.70, 0.97 );
		col = vec3( blue * lambert );
	}
	else
	{
		col = vec3( 0.0 );
	}
	gl_FragColor = vec4( col, 1.0 );
}