CloseEncounters.ino

// "Close Encounters" by Jason Coon
// https://gist.github.com/pup05/d4c935566ec82731fece
// 
// The start of the main light bar on the ship in Close Encounters of the Third Kind: https://www.youtube.com/watch?v=S4PYI6TzqYk
// Multiple anti-aliased light bars running in alternating directions, now just needs the pulses of color.
// 
// A slight modification of Mark Kriegsman's Anti-aliased light bar example: http://pastebin.com/g8Bxi6zW
// https://plus.google.com/u/0/112916219338292742137/posts/2VYNQgD38Pw

#include <FastLED.h>

#define LED_PIN     3
#define CLOCK_PIN   2
#define COLOR_ORDER GRB
#define CHIPSET     APA102
#define NUM_LEDS    63
#define BRIGHTNESS  240

CRGB leds[NUM_LEDS];

int Width = 4; // width of each light bar, in whole pixels

const int barCount = 8;
int bars[barCount];

int     F16delta = 1; // how many 16ths of a pixel to move the Fractional Bar
uint16_t Fhue16 = 0; // color for Fractional Bar

int InterframeDelay = 40; //ms

void setup()
{
    FastLED.addLeds<CHIPSET, LED_PIN, CLOCK_PIN, BGR, DATA_RATE_MHZ(12)>(leds, NUM_LEDS);
    FastLED.setBrightness(BRIGHTNESS);

    for (int i = 0; i < barCount; i++) {
        bars[i] = i * ((NUM_LEDS * 16) / barCount);
    }
}

// Draw a "Fractional Bar" of light starting at position 'pos16', which is counted in
// sixteenths of a pixel from the start of the strip.  Fractional positions are
// rendered using 'anti-aliasing' of pixel brightness.
// The bar width is specified in whole pixels.
// Arguably, this is the interesting code.
void drawFractionalBar(int pos16, int width, uint8_t hue, uint8_t sat)
{
    int i = pos16 / 16; // convert from pos to raw pixel number
    uint8_t frac = pos16 & 0x0F; // extract the 'factional' part of the position

    // brightness of the first pixel in the bar is 1.0 - (fractional part of position)
    // e.g., if the light bar starts drawing at pixel "57.9", then
    // pixel #57 should only be lit at 10% brightness, because only 1/10th of it
    // is "in" the light bar:
    //
    //                       57.9 . . . . . . . . . . . . . . . . . 61.9
    //                        v                                      v
    //  ---+---56----+---57----+---58----+---59----+---60----+---61----+---62---->
    //     |         |        X|XXXXXXXXX|XXXXXXXXX|XXXXXXXXX|XXXXXXXX |  
    //  ---+---------+---------+---------+---------+---------+---------+--------->
    //                   10%       100%      100%      100%      90%        
    //
    // the fraction we get is in 16ths and needs to be converted to 256ths,
    // so we multiply by 16.  We subtract from 255 because we want a high
    // fraction (e.g. 0.9) to turn into a low brightness (e.g. 0.1)
    uint8_t firstpixelbrightness = 255 - (frac * 16);

    // if the bar is of integer length, the last pixel's brightness is the
    // reverse of the first pixel's; see illustration above.
    uint8_t lastpixelbrightness = 255 - firstpixelbrightness;

    // For a bar of width "N", the code has to consider "N+1" pixel positions,
    // which is why the "<= width" below instead of "< width".

    uint8_t bright;
    for (int n = 0; n <= width; n++) {
        if (n == 0) {
            // first pixel in the bar
            bright = firstpixelbrightness;
        }
        else if (n == width) {
            // last pixel in the bar
            bright = lastpixelbrightness;
        }
        else {
            // middle pixels
            bright = 255;
        }

        leds[i] += CHSV(hue, sat, bright);
        i++;
        if (i == NUM_LEDS) i = 0; // wrap around
    }
}

void loop()
{
    // Draw everything:
    // clear the pixel buffer
    memset8(leds, 0, NUM_LEDS * sizeof(CRGB));

    for (int i = 0; i < barCount; i++) {
        int bar = bars[i];

        // Update the "Fraction Bar" by 1/16th pixel every time
        if (i % 2 == 0)
            bar += F16delta;
        else
            bar -= F16delta;

        // wrap around at end
        // remember that F16pos contains position in "16ths of a pixel"
        // so the 'end of the strip' is (NUM_LEDS * 16)
        if (bar >= (NUM_LEDS * 16))
            bar -= NUM_LEDS * 16;
        else if (bar < 0)
            bar = (NUM_LEDS * 16) - 1;

        // draw the Fractional Bar, length=4px
        drawFractionalBar(bar, Width, 0, 0);

        bars[i] = bar;
    }

    FastLED.show();
    FastLED.delay(InterframeDelay);
}

Cool. Thanks.