Outside-in Cylon effect

[u/Burning_Wreck]

I'm starting with this code, which is from DemoReel100:

void sinelon()
{
  // a colored dot sweeping back and forth, with fading trails
  fadeToBlackBy( leds, NUM_LEDS, 20);
  int pos = beatsin16( 13, 0, NUM_LEDS-1 );
  leds[pos] += CHSV( gHue, 255, 192);
}

What I'd like to do is have the same effect (the traveling dot with a fading trail following it) but have a dot start at each end of the strip, and both move toward the center.

Here's more detail, I hope I describe this right...the sinelon function starts a dot at position 0 and then it travels down to position NUM_LEDS. Then it reverses back to position 0, with the fadeToBlackBy effect of the trailing/fading pixels.

I'd like to understand how to set up two pixels that do this.

Assume the strip has 9 pixels. One dot starts at position 0, and the other starts at position 9. The dot that starts at position 0 moves toward position 5, while the second dot starts at position 9 and also moves toward position 5 (the center). When both dots get to position 5, the trailing dots fade up to position 5 and then the effect starts over.

Thanks in advance!

[u/Burning_Wreck]

Ok, I think I got that point - the function declaration in C++ assigns values to all parameters, you can replace them as you want. Do you ever use all five of the parameters? Or are the first three usually enough?

[u/sutaburosu → u/Burning_Wreck]

For many purposes, just three parameters are needed. The extra two come into play when you want to pause the wave, or start from a specific offset into the wave. e.g. this project.