``````/* I bought 4 of the 8x8 NeoPixel panels with the intention to made a 16x16 display
but I'm having trouble wrapping my head around addressing each of the LEDs.
I wired up the panels like this
1,3
2,4
*/

#include <FastLED.h>

#define kMatrixWidth 16
#define kMatrixHeight 16
#define NUM_LEDS ((kMatrixWidth) * (kMatrixHeight))

CRGB leds[NUM_LEDS];

uint16_t XY(int8_t x, int8_t y) {
if (x >= kMatrixWidth || y >= kMatrixHeight || x < 0 || y < 0)
return -1;

const uint8_t panel_size = 8;
const bool horizontal_tiling = 0; // set to 1 if panels are chained in X first
const bool serpentine_tiling = 0; // set to 1 if odd rows/columns of panels are reversed
const bool serpentine_panels = 1; // set to 1 if panels have odd rows of LEDs reversed

const uint8_t x_panels = kMatrixWidth / panel_size;
const uint8_t y_panels = kMatrixHeight / panel_size;

// determine which panel this pixel falls on
uint8_t x_panel = x / panel_size;
uint8_t y_panel = y / panel_size;

// for serpentine layouts of panels
if (serpentine_tiling) {
if (horizontal_tiling) {
if (y_panel & 1) // odd rows of panels are reversed
x_panel = x_panels - 1 - x_panel;
} else {
if (x_panel & 1) // odd columns of panels are reversed
y_panel = y_panels - 1 - y_panel;
}
}

// where in the leds[] array does this panel start
uint16_t panel_offset = panel_size * panel_size;
if (horizontal_tiling)
panel_offset *= x_panels * y_panel + x_panel;
else
panel_offset *= y_panels * x_panel + y_panel;

// constrain coordinates to the panel size
x %= panel_size;
y %= panel_size;

// serpentine layout panels have odd rows reversed
if (serpentine_panels && (y & 1))
x = panel_size - 1 - x;

return panel_offset + x + y * panel_size;
}

void setup() {
FastLED.addLeds<WS2812B, 3, GRB>(leds, NUM_LEDS);
}

void loop() {
static uint16_t startHue = 0;
static uint16_t xPhase = 0;
static int16_t xPhaseMul = 2 * 256;
static int16_t yPhaseMul = 256;
static int8_t yPhaseMulStep = 3;
static int8_t xPhaseMulStep = 2;

startHue += 512;
xPhase += 512;

yPhaseMul += yPhaseMulStep;
if (yPhaseMul <= 96)
yPhaseMulStep = random8(4) + 1;
if (yPhaseMul >= 8 * 128)
yPhaseMulStep = -random8(4) - 1;

xPhaseMul += xPhaseMulStep;
if (xPhaseMul <= 96)
xPhaseMulStep = random8(4) + 1;
if (xPhaseMul >= 8 * 128)
xPhaseMulStep = -random8(4) - 1;

uint16_t pixelHue = startHue;
for (uint16_t i = 0; i < 384; i++) {
uint16_t x = 32767 + cos16(xPhase + i * xPhaseMul);
uint16_t y = 32767 + sin16(i * yPhaseMul);
x /= 256 / (kMatrixWidth - 1);
y /= 256 / (kMatrixHeight - 1);
CRGB col = ColorFromPalette(RainbowStripeColors_p, pixelHue >> 8, 255, LINEARBLEND);
wu_pixel(x, y, col);
pixelHue += 128;
}
FastLED.show();
FastLED.clear();
}

void wu_pixel(uint16_t x, uint16_t y, CRGB &col) {
// extract the fractional parts and derive their inverses
uint8_t xx = x & 0xff, yy = y & 0xff, ix = 255 - xx, iy = 255 - yy;
// calculate the intensities for each affected pixel
#define WU_WEIGHT(a, b) ((uint8_t)(((a) * (b) + (a) + (b)) >> 8))
uint8_t wu[4] = {WU_WEIGHT(ix, iy), WU_WEIGHT(xx, iy),
WU_WEIGHT(ix, yy), WU_WEIGHT(xx, yy)
};
#undef WU_WEIGHT
// multiply the intensities by the colour, and saturating-add them to the pixels
for (uint8_t i = 0; i < 4; i++) {
uint8_t local_x = (x >> 8) + (i & 1);
uint8_t local_y = (y >> 8) + ((i >> 1) & 1);
if (uint16_t xy = XY(local_x, local_y); xy < NUM_LEDS)
leds[xy] += col % wu[i];
}
}
``````