Pixelblaze pattern: a block of lights chases around a circle while the touch sensor is touched

pb-touch-chaser.js

// While the capacitive sensor is touched, a block of light chases around the
// LED strip.

timer = 0 // ms since last position update
period = 100 // ms between position updates
hue = 0
export var center = 0 // the center of the light block

export function beforeRender(delta) {
  isTouching = touchRead(T4) > .6
  timer += delta
  if (timer > period) {
    timer -= period
    // update the position if the sensor is touched
    if (isTouching) {
      center = (center + 1) % pixelCount
      hue = (hue + .01) % 1
    }
  }
}

export function render(index) {
  // Compute the distance from the current pixel to the center, considering the
  // strip as a circle (so that the last pixel is next to the first one).
  //
  // `abs(index - center)` is the distance from the current pixel (`index`) to
  // the center of the block, staying inside the LED strip. `abs(index -
  // pixelCount - center)` is the distance going off one end and back onto the
  // other. `min(…, …)` is whichever is smaller.
  distance = min(abs(index - center), abs(index - pixelCount - center))
  hsv(hue, 1, distance < 3) // distance < 3 is 1 when distance < 3, else 0
}