raymarching!

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_pos = vec3( 0.0, 1.0, 1.0 );

float sphere( vec3 pos, float rad )
{
	return length(pos) - rad;
}

float scene_distance( vec3 pos )
{
	float d = sphere( pos, 1.0 );
	return d;
}

vec3 scene_normal( vec3 pos )
{
	float delta = 0.0001;
	vec3 normal;
	normal.x = scene_distance( vec3( pos.x + delta, pos.y, pos.z ) ) - scene_distance( vec3( pos.x - delta, pos.y, pos.z ) );
	normal.y = scene_distance( vec3( pos.x, pos.y + delta, pos.z ) ) - scene_distance( vec3( pos.x, pos.y - delta, pos.z ) );
	normal.z = scene_distance( vec3( pos.x, pos.y, pos.z + delta ) ) - scene_distance( vec3( pos.x, pos.y, pos.z - delta ) );
	return normalize( normal );
}

void main( void )
{
	// Coord
	vec2 uv_raw = 2.0 * ( gl_FragCoord.xy / resolution.xy )  - 1.0;
	vec2 uv = uv_raw;
	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
	bool is_hit = false;
	vec3 ray_pos = eye_pos;
	vec3 ray_vec = normalize( eye_vec + uv.x * eye_left + uv.y * eye_up );
	for ( int i = 0; i < 100; ++i )
	{
		float d = scene_distance( ray_pos );
		if ( d < 0.001 )
		{
			is_hit = true;
		}
		ray_pos += d * ray_vec;
	}
	
	// Color
	vec3 rgb = vec3( 0.0 );
	if ( is_hit )
	{
		vec3 normal = scene_normal( ray_pos );
		vec3 blue = vec3( 0.0, 0.7, 0.97 );
		rgb = dot( normal, light_pos ) * blue;
	}
	else
	{
		rgb = vec3( ( uv_raw.y + 1.0 ) * 0.5 );
	}
	
	// vignette
	rgb *= smoothstep( 2.0 , 0.5, dot( uv_raw, uv_raw ) );
	
	gl_FragColor = vec4( rgb, 1.0 );
}