box.glsl

#ifdef GL_ES
precision mediump float;
#endif

#extension GL_OES_standard_derivatives : enable

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


//反復回数(constで書く方も多い)
         #define ITE_MAX      190

#define DIST_COEFF   .36
 //打ち切り係数
         #define DIST_MIN     0.01

         //t最大
         #define DIST_MAX     10000.0


  #define inf 100000
	#define PI 3.14159276

	#define UnitWindow_Size 50.0

mat3 rotM(vec3 axis,float angle){

  axis = normalize(axis);
	float s = sin(angle);
	float c = cos(angle);
	float oc = 1.0 - c;

	return mat3(oc * axis.x * axis.x + c, oc * axis.x * axis.y - axis.z * s, oc * axis.z * axis.x + axis.y * s,
	oc * axis.x * axis.y + axis.z * s, oc * axis.y * axis.y + c, oc * axis.y * axis.z - axis.x * s,
	oc * axis.z * axis.x - axis.y * s, oc * axis.y * axis.z + axis.x * s, oc * axis.z * axis.z + c);}
vec3 GenRay(vec3 dir,vec3 up,float angle){

	vec2 p = (gl_FragCoord.xy * 2.0 - resolution) / min(resolution.x, resolution.y);
	vec3 u = normalize(cross(up, dir));
	vec3 v = normalize(cross(dir, u));

	float fov = angle * PI * 0.5 / 180.;

	return  normalize(sin(fov) * u * p.x + sin(fov) * v * p.y + cos(fov) * dir);}
float map(vec3 p){

float d = 0.;
//p = mod(p,12.) - vec3(6);
//d = length(p) - 3.;
d = length(max(abs(p)-vec3(1.,2.,1.),0.0));
//d = hivemap(p);
return d;

}
vec3 getnormal(vec3 p){

float d = 0.01;
return normalize(vec3(
map(p + vec3(d, 0.0, 0.0)) - map(p + vec3(-d, 0.0, 0.0)),
map(p + vec3(0.0, d, 0.0)) - map(p + vec3(0.0, -d, 0.0)),
map(p + vec3(0.0, 0.0, d)) - map(p + vec3(0.0, 0.0, -d))
));
}
void main( void) { 
vec3 l = normalize(vec3(.0, -.99, .99));
//eye座標
vec3 pos = vec3(1.+2.*cos(time),  4. * sin(time), 1.5);
vec3 target = vec3(0.,0., 0.);
vec3 center_dir = (target - pos);
vec3 dir;
vec3 up = vec3(.0, 0., 1.);
dir = GenRay(normalize(center_dir), up, 120.);


float t = 0.0;
         	
		 float dist = 0.;
         	//SphereTracing。ここintersectって名前で別に作る人も多いです
         	for(int i = 0 ; i < ITE_MAX; i++) {

         		//形状表現した陰関数を反復しながら解く
         		//0(DIST_MIN)に近くなったら解に近いので打ち切り
         		dist = map((t * dir + pos));
         		if(dist < DIST_MIN) {
				break;
			}
         		
         		//tを更新。DIST_COEFFは複雑な形状を描画する際に小さく為につけています。
         		//ちょっとずつレイを進める事ができます。
         		t += dist * DIST_COEFF;
			
			if(t > DIST_MAX){
				break;
			}
         	}

//option形状の近くの位置を出しておく
vec3 ip = pos + dir * t;
//色を作ります。ここでは進めたtの位置(深度)をただ出力するだけ

vec3 color = vec3(0.);
 vec3 n = getnormal(ip);
if(dist < DIST_MIN){
	float diff = dot(l,n);
	color = vec3(0.3,0.8,0.9) * clamp(diff,0.1,1.);
			
	color += vec3(.5) * clamp(dot(n,normalize(dir+l)),0.,1.);
	//color += ip.z*vec3(2.0,1.,0.);
}
color += clamp((1.-20./t),0.,1.)*vec3(.8,.9,.9);
        	
gl_FragColor = vec4(color, 1.0);
			
}