ray_marching_000

precision mediump float;
uniform float time;
uniform vec2  mouse;
uniform vec2  resolution;

const float sphereSize = 1.0;

float distanceFunc(vec3 p){
	return length(p) - sphereSize;
}

void main(void){
	// fragment position
	vec2 p = (gl_FragCoord.xy * 2.0 - resolution) / min(resolution.x, resolution.y);
	
	// camera
	vec3 cPos = vec3(0.0,  0.0,  3.0);
	vec3 cDir = vec3(0.0,  0.0, -1.0);
	vec3 cUp  = vec3(0.0,  1.0,  0.0);
	vec3 cSide = cross(cDir, cUp);
	float targetDepth = 0.1;
	
	// ray
	vec3 ray = normalize(cSide * p.x + cUp * p.y + cDir * targetDepth);
	
	// marching loop
	float distance = 0.0; // レイとオブジェクト間の最短距離
	float rLen = 0.0;     // レイに継ぎ足す長さ
	vec3  rPos = cPos;    // レイの先端位置
	for(int i = 0; i < 16; i++){
		distance = distanceFunc(rPos);
		rLen += distance;
		rPos = cPos + ray * rLen;
	}
	
	// hit check
	if(abs(distance) < 0.001){
		gl_FragColor = vec4(vec3(1.0), 1.0);
	}else{
		gl_FragColor = vec4(vec3(0.0), 1.0);
	}
}