Continous running light with fading trail In examples of FastLED library, there's the animation of a dot sweeping back and forth, with fading trails (file "DemoReel100", animation "sinelon"). How can I alter the code so instead of moving back, the dot begins at LED #1 again; so when using a LED ring, then the movement is continuous and circular.
Since the code will be part of a more complex project with reading of button states etc, the animation code has to be non-blocking, i.e. delay() is not an option.

void sinelon()
{
fadeToBlackBy( leds, NUM_LEDS, 20);
int pos = beatsin16( 13, 0, NUM_LEDS-1 );
leds[pos] += CHSV( gHue, 255, 192);
}
If you look at the surrounding methods, you'll see that 'fadeToBlackBy' will give a fading effect on anything you feed in. You'll want to locate method 'beatsin16' and then edit it yourself so that it doesn't bounce back but restarts the counter at the first LED. (hint: phase_offset)

You'll find the code snippet you want to copy in lib8tion.h

/// beatsin16 generates a 16-bit sine wave at a given BPM,
///           that oscillates within a given range.
LIB8STATIC uint16_t beatsin16( accum88 beats_per_minute, uint16_t lowest = 0, uint16_t highest = 65535,
                               uint32_t timebase = 0, uint16_t phase_offset = 0)
{
    uint16_t beat = beat16( beats_per_minute, timebase);
    uint16_t beatsin = (sin16( beat + phase_offset) + 32768);
    uint16_t rangewidth = highest - lowest;
    uint16_t scaledbeat = scale16( beatsin, rangewidth);
    uint16_t result = lowest + scaledbeat;
    return result;
}