fwidth：任何缩放都清晰的边

void main() {
  vec2 p = (gl_FragCoord.xy - 0.5 * uResolution) / min(uResolution.x, uResolution.y);
  p *= 6.000;                        // 放大坐标 → 图案变密
  float d = length(fract(p) - 0.5) - 0.3;     // 每格一个圆的 SDF
  float fixedMask = 1.0 - smoothstep(0.0, 0.010, d);
  float w = fwidth(d);                    // 相邻像素之间 d 变了多少
  float smartMask = 1.0 - smoothstep(-w, w, d);
  float mask = vUv.x < 0.5 ? fixedMask : smartMask;
  vec3 color = mix(vec3(0.06, 0.10, 0.14), vec3(0.48, 0.83, 0.69), mask);
  if (abs(vUv.x - 0.5) < 0.002) color = vec3(1.0);
  gl_FragColor = vec4(color, 1.0);
}