Simple feedback effect in processing / glsl... feedback.glsl belongs in the data folder

feedback.glsl

uniform sampler2D texture; // the current canvas is passed to this shader in Processing as "texture" which is a bad name for it but whatever
uniform vec2 resolution; //set automatically by Processing
uniform float time; 	//set manually in code

void main(){
	vec2 uv = gl_FragCoord.xy / resolution.xy; // coordinate with 0,0 at bottom left, and 1,1 at top right
	vec2 offset = vec2(cos(time), sin(time)) / resolution.xy; // the rotating offset to sample a neighbour at
	vec4 thisPixelColor = texture2D(texture, uv);
	vec4 nearPixelColor = texture2D(texture, uv + offset);
	vec4 finalColor = mix(thisPixelColor, nearPixelColor, 0.5); // lerp between the two colors, 0.5 specifies how quickly the effect fades into the background
	gl_FragColor = vec4(finalColor.rgb, 1.);
}

feedback.pde

    PShader feedback;
    float t;
    
    void setup() {
      size(640, 640, P2D);
      smooth(16);
      background(0);
      colorMode(HSB, 1, 1, 1, 1);
      feedback = loadShader("feedback.glsl");
    }
    
    void draw() {
      t += 0.001;
      translate(width / 2, height / 2);
      //rotate(t * 10);
      fill(0, 0.1);
      strokeWeight(3);
      stroke(t % 1, 1, 1);
      rectMode(CENTER);
      rect(0, 0, 120, 120);
      feedback.set("time", t);
      filter(feedback);
    }