fract 与 mod：无限重复

void main() {
  vec2 grid = vUv * 5.000;
  vec2 cell = fract(grid) - 0.5;
  float checker = mod(floor(grid.x) + floor(grid.y), 2.0);
  float mask = 1.0 - smoothstep(0.300, 0.300 + 0.015, length(cell));
  vec3 ink = mix(vec3(0.48, 0.83, 0.69), vec3(0.96, 0.43, 0.30), checker);
  vec3 color = mix(vec3(0.06, 0.10, 0.14), ink, mask);
  gl_FragColor = vec4(color, 1.0);
}