Ray-Sphere 계산

수식

코드

uniform vec3 uResolution;
uniform float uTime;
uniform vec4 uMouse;

// v = a -> 0
// v = b -> 1 
// v = (a+b)/2 -> 0.5
float remap01(float a, float b, float v) {
  return (v - a) / (b - a);
}

void main() {
  vec2 uv = (gl_FragCoord.xy - .5 * uResolution.xy) / uResolution.y;

  vec3 col = vec3(0);
  vec3 Ro = vec3(0);
  vec3 Rd = normalize(vec3(uv.x, uv.y, 1.));
  vec3 S = vec3(0, 0, 3);
  float R = 1.;

  float tp = dot(S - Ro, Rd);
  vec3 Ptp = Ro + Rd * tp;
  float y = length(S - Ptp);
  
  if(y < R) {
    float x = sqrt(R*R - y*y);
    float t1 = tp - x;
    float t2 = tp + x;

    float c = remap01(S.z, S.z - R, t1);
    col = vec3(c);
  }
  
  gl_FragColor = vec4(col, 1.0);
}

결과