benjivers/val Public Public: anyone can read this; the crew can change it.

/**

 * The frame budget: what the last second of frames cost, and one knob.

 *

 * The renderer's price is the number of columns it draws, and the right

 * number is not knowable from here — it depends on the machine, the window,

 * the battery and whatever else the browser is doing. So it is measured: a

 * second of frames at a time, and if the mean frame is over the budget the

 * world is drawn a rung coarser (see resolution.js), and a rung finer again

 * when there is room.

 *

 * It must not flap, because a resolution changing twice a second is more

 * visible than a resolution that is simply low. Three things stop it:

 * coarsening and refining have different thresholds, refining needs two

 * windows of headroom in a row, and it never refines past the rung the

 * window started on.

 *

 * Measurement only. Nothing here is sent anywhere or told to the simulation.

 */

/** Seconds of frames behind one decision. */

export const WINDOW = 1;

/** Mean milliseconds a frame: over this is over budget, under this has room. */

export const SLOW = 20;

export const FAST = 13;

/** Windows of headroom before a rung is given back. */

export const PATIENCE = 2;

export function makeBudget(base = 0, max = 6) {

  return { base, max, level: base, frames: 0, total: 0, since: 0, good: 0, fps: 0, mean: 0 };

}

/**

 * One frame, `ms` long, drawn at `now` seconds. Returns true when the level

 * moved — the caller resizes what it draws into — and updates `fps` and

 * `mean` at the end of every window, for the readout to print.

 */

export function measure(budget, ms, now) {

  budget.frames++;

  budget.total += ms;

  if (budget.since === 0) {

    budget.since = now;

    return false;

  }

  const span = now - budget.since;

  if (span < WINDOW) return false;

  budget.mean = budget.total / budget.frames;

  budget.fps = budget.frames / span;

  budget.frames = 0;

  budget.total = 0;

  budget.since = now;

  if (budget.mean > SLOW) {

    budget.good = 0;

    if (budget.level >= budget.max) return false;

    budget.level++;

    return true;

  }

  if (budget.mean < FAST && budget.level > budget.base) {

    budget.good++;

    if (budget.good < PATIENCE) return false;

    budget.good = 0;

    budget.level--;

    return true;

  }

  budget.good = 0;

  return false;

}