Feedback is a powerful feature which allow Fragment to have access to the previously rendered frame.

The previously rendered frame can then be manipulated in the main fragment and displayed back generating a feedback loop, effects such as delay, reverberation etc. can be produced that way.

One must be careful when using this feature because the sound can become pretty loud depending on how the rendered frame is manipulated, for example, with static visuals, if you add the previous frame to the current frame, the result will be pretty much white!


The previous frame fragment shader cannot be edited for now, its source-code is

void main () {
  vec2 uv = gl_FragCoord.xy / resolution;
  vec4 c = texture(colorInput, uv);
  vec4 s = texture(synthInput, uv);
  fragColor = c;
  synthOutput = s;


The previous frame is accessible as a texture within the main shader, example

vec4 pframe = texture(pFrame, vec2(uv.x, uv.y));

When WebGL 2 is supported, there is also an independant definition for the synth. data frame

vec4 pframe_synth = texture(pFrameSynth, vec2(uv.x, uv.y));