failed: added rotation fail

failed/rotation_gone_wrong.glsl

@@ -0,0 +1,38 @@
+#ifdef GL_ES
+precision mediump float;
+#endif uniform vec2 u_resolution;
+
+uniform float u_time;
+
+#define PI 3.14159265358979323846
+vec2 rotate2D(vec2 _st, float _angle){
+  _st -= 0.5;
+  _st = mat2(cos(_angle),-sin(_angle), sin(_angle),cos(_angle)) * _st;
+  _st += 0.5;
+  return _st;
+}
+
+vec2 tile(vec2 _st, float _zoom){
+  _st *= _zoom;
+  return fract(_st);
+}
+
+vec2 get_st() {
+  return gl_FragCoord.xy/min(u_resolution.x, u_resolution.y);
+}
+
+vec3 line(float width, float angle, vec3 color, vec2 st) {
+  float e = 0.003;
+  st -= vec2(0.5);
+  st *= rotate2D(st, angle);
+  return color*((smoothstep(-e-width/2., 0.-width/2., st.x)-smoothstep(0.+width/2., e+width/2., st.x)));
+}
+
+void main() {
+  vec2 st = gl_FragCoord.xy/u_resolution.xy;
+  vec3 color = vec3(0.5);
+
+  color += line(0.2, PI, vec3(0.1,0.,0.),st+0.2);
+  color += line(.02, 2./PI, vec3(0.9), st);
+  gl_FragColor = vec4(color, 1.0);
+}