Screen Melt

Screen Melt Shader - Anton Gerdelan

#version 300 es
// "Screen Melt" fragment shader. GLSL.
// by Anton Gerdelan Dec. 2021
precision highp float;

in vec2 v_st;
uniform float u_time;
uniform sampler2D u_texture;
out vec4 o_frag_colour;

float rand_delay() {
  float w = 1280.0;
  float f = gl_FragCoord.x / 1280.0;
  float n_snakes = 160.0; // i think it was 2 pixel wide on a 320px
  float column = floor( n_snakes * f );
  float max_delay = 0.45;
  // this is terrible but it might work
  float r = clamp( sin( column * 5.5 * cos( column * 0.16) * 0.32124 ) * 0.5 + 0.5, 0.0, 1.0 ) * max_delay;
  return r;
}

void main() {
  float effect_time = 2.0;
  float r = rand_delay();
  float t = mod( u_time, effect_time );
  vec2 st = vec2( v_st.s, v_st.t );
  if ( t > r * 1.0 ) {
    st.t -= (t - r ) ;
  }
  vec4 texel    = texture( u_texture, st );
  o_frag_colour = texel; //o_frag_colour * 0.25 + texel * 0.75;

if ( st.t < 0.0 || st.t > 1.0 ) {
    o_frag_colour = vec4( 0.0, 0.0, 0.0, 1.0 );
  }
  
  // visualise the effect time:
  //o_frag_colour = vec4( 0.0, t / effect_time , 0.0, 1.0 );

// visualise the column delays:
  //o_frag_colour = vec4( rand_delay(), 0.0 , 0.0, 1.0 );
}