shader_type canvas_item;

const float TAU = 6.28319;

uniform float speed = 1.0;
uniform float cycle_offset = 0.0;
uniform float wave_length = 1.0;
uniform float thickness = 0.05;

float plot(vec2 st, float pct) {
  return  step( pct - thickness, st.x) -
          step( pct + thickness, st.x);
}

void fragment() {
	float sin_time = fract(TIME * floor(speed)) * TAU;
	float x = sin(UV.y * wave_length + sin_time + cycle_offset)*0.5+0.5;
	COLOR = COLOR * vec4(1.0, 1.0, 1.0, plot(UV * vec2(1.2, 1.0) + vec2(-0.1, 0.0), x));
}