# 【GLSL】回転するボックス

```#define PI 3.14159265359
#define TWO_PI PI * 2.0

precision mediump float;

uniform float u_time;
uniform vec2 u_mouse;
uniform vec2 u_resolution;

vec3 rotateX(vec3 p, float theta) {
float c = cos(-theta);
float s = sin(-theta);

mat3 m = mat3(vec3(1, 0.0, 0.0),
vec3(0.0, c, -s),
vec3(0.0, s, c));
return m * p;
}

vec3 rotateY(vec3 p, float theta) {
float c = cos(-theta);
float s = sin(-theta);

mat3 m = mat3(vec3(c, 0.0, s),
vec3(0.0, 1.0, 0.0),
vec3(-s, 0.0, c));
return m * p;
}

vec3 rotateZ(vec3 p, float theta) {
float c = cos(-theta);
float s = sin(-theta);

mat3 m = mat3(vec3(c, -s, 0.0),
vec3(s, c, 0.0),
vec3(0.0, 0.0, 1.0));
return m * p;
}

float calcBoxDistance(vec3 p, vec3 size) {
return length(max(abs(p) - size, 0.0));
}

float calcDistance(vec3 p) {
float t = u_time * 0.0003;
vec3 size = vec3(0.3, 0.3, 0.3);
float d = calcBoxDistance(rotateZ(rotateY(rotateX(p, t), t * 2.0), t * 3.0), size);
return d;
}

vec3 calcNormal(vec3 p) {
float delta = 0.00001;
return normalize(vec3(
calcDistance(p + vec3(delta, 0.0, 0.0)) - calcDistance(p - vec3(delta, 0.0, 0.0)),
calcDistance(p + vec3(0.0, delta, 0.0)) - calcDistance(p - vec3(0.0, delta, 0.0)),
calcDistance(p + vec3(0.0, 0.0, delta)) - calcDistance(p - vec3(0.0, 0.0, delta))
));
}

void main(void) {
vec2 st = (gl_FragCoord.xy * 2.0 - u_resolution) / min(u_resolution.x, u_resolution.y);

vec3 cameraPosition = vec3(0.0, 0.0, 5.0);
vec3 rayDirection = normalize(vec3(st, 0.0) - cameraPosition);
vec3 rayPosition = cameraPosition;
float radian = u_time * 0.0003;
vec3 lightPosition = vec3(5.0, 5.0, 5.0);
vec3 color = vec3(0.0);
for (int i = 0; i < 64; i++) {
float d = calcDistance(rayPosition);
if (d < 0.0001) {
vec3 normal = calcNormal(rayPosition);
float weight = dot(normal, normalize(lightPosition));
color = vec3(1.0) * max(weight, 0.0) + vec3(0.1);
break;
}
rayPosition += rayDirection * d;
}
gl_FragColor = vec4(color, 1.0);
}
```