【GLSL】短辺の範囲が[-1, 1]になるように座標を変換する

See the Pen coordinate transformation by aadebdeb (@aadebdeb) on CodePen.

precision mediump float;

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


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

  gl_FragColor = vec4(vec3(length(st)), 1.0);
}