3_1_2_Random_Maze.glsl

#ifdef GL_ES
precision mediump float;
#endif

#define PI 3.14159265358979323846

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

float random(in vec2 _st)
{
  return fract(sin(dot(_st.xy,vec2(12.9898,78.233)))*43758.5453123);
}

vec2 truchetPattern(in vec2 _st,in float _index)
{
  _index=fract((_index-0.5)*2.0);
  if(_index>0.75)
  {
    _st=vec2(1.0)-_st;
  }
  else if(_index>0.5)
  {
    _st=vec2(1.0-_st.x,_st.y);
  }
  else if(_index>0.25)
  {
    _st=1.0-vec2(1.0-_st.x,_st.y);
  }
  return _st;
}

void main()
{
  vec2 st=gl_FragCoord.xy/u_resolution.xy;
  st*=10.0;
  // st=(st-vec2(5.0))*abs(sin(u_time*0.2))*0.5;
  // st.x+=u_time*3.0;

  vec2 ipos=floor(st); // integer
  vec2 fpos=fract(st); // fraction

  vec2 tile=truchetPattern(fpos,random(ipos));

  float color=0.0;

  // Maze 迷宫
  // color=smoothstep(tile.x-0.3,tile.x,tile.y)-smoothstep(tile.x,tile.x+0.3,tile.y);

  // Circles
  color=(step(length(tile),0.6)-step(length(tile),0.4))+
  (step(length(tile-vec2(1.)),0.6)-step(length(tile-vec2(1.)),0.4));

  // Truchet (2 triangles)
  // color=step(tile.x,tile.y);

  gl_FragColor=vec4(vec3(color),1.0);
}