// This version uses bit-banged SPI.
// If you see tearing (jagged edges on the circles) try the version
// which uses AVR's hardware SPI peripheral:
// https://wokwi.com/arduino/projects/318868939929027156
#define CLK 13
#define DIN 12
#define CS 14
#define X_SEGMENTS 4
#define Y_SEGMENTS 4
#define NUM_SEGMENTS (X_SEGMENTS * Y_SEGMENTS)
// a framebuffer to hold the state of the entire matrix of LEDs
// laid out in raster order, with (0, 0) at the top-left
byte fb[8 * NUM_SEGMENTS];
void shiftAll(byte send_to_address, byte send_this_data)
{
digitalWrite(CS, LOW);
for (int i = 0; i < NUM_SEGMENTS; i++) {
shiftOut(DIN, CLK, MSBFIRST, send_to_address);
shiftOut(DIN, CLK, MSBFIRST, send_this_data);
}
digitalWrite(CS, HIGH);
}
void setup() {
Serial.begin(115200);
pinMode(CLK, OUTPUT);
pinMode(DIN, OUTPUT);
pinMode(CS, OUTPUT);
// Setup each MAX7219
shiftAll(0x0f, 0x00); //display test register - test mode off
shiftAll(0x0b, 0x07); //scan limit register - display digits 0 thru 7
shiftAll(0x0c, 0x01); //shutdown register - normal operation
shiftAll(0x0a, 0x0f); //intensity register - max brightness
shiftAll(0x09, 0x00); //decode mode register - No decode
}
void loop() {
static int16_t sx1 = 15 << 8, sx2 = sx1, sy1, sy2;
sx1 = sx1 - (sy1 >> 6);
sy1 = sy1 + (sx1 >> 6);
sx2 = sx2 - (sy2 >> 5);
sy2 = sy2 + (sx2 >> 5);
static byte travel = 0;
travel--;
byte *dst = fb;
byte output = 0;
int8_t x_offset = (sx1 >> 8) - X_SEGMENTS * 4;
int8_t y_offset = (sx2 >> 8) - Y_SEGMENTS * 4;
uint8_t screenx, screeny, xroot, yroot;
uint16_t xsumsquares, ysumsquares, xnextsquare, ynextsquare;
int8_t x, y;
// offset the origin in screen space
x = x_offset;
y = y_offset;
ysumsquares = x_offset * x_offset + y * y;
yroot = int(sqrtf(ysumsquares));
ynextsquare = yroot*yroot;
// Quadrant II (top-left)
screeny = Y_SEGMENTS * 8;
while (y < 0 && screeny) {
x = x_offset;
screenx = X_SEGMENTS * 8;
xsumsquares = ysumsquares;
xroot = yroot;
if (x < 0) {
xnextsquare = xroot * xroot;
while (x < 0 && screenx) {
screenx--;
output <<= 1;
output |= ((xroot + travel) & 8) >> 3;
if (!(screenx & 7))
*dst++ = output;
xsumsquares += 2 * x++ + 1;
if (xsumsquares < xnextsquare)
xnextsquare -= 2 * xroot-- - 1;
}
}
// Quadrant I (top right)
if (screenx) {
xnextsquare = (xroot + 1) * (xroot + 1);
while (screenx) {
screenx--;
output <<= 1;
output |= ((xroot + travel) & 8) >> 3;
if (!(screenx & 7))
*dst++ = output;
xsumsquares += 2 * x++ + 1;
if (xsumsquares >= xnextsquare)
xnextsquare += 2 * ++xroot + 1;
}
}
ysumsquares += 2 * y++ + 1;
if (ysumsquares < ynextsquare)
ynextsquare -= 2 * yroot-- - 1;
screeny--;
}
// Quadrant III (bottom left)
ynextsquare = (yroot + 1) * (yroot + 1);
while (screeny) {
x = x_offset;
screenx = X_SEGMENTS * 8;
xsumsquares = ysumsquares;
xroot = yroot;
if (x < 0) {
xnextsquare = xroot * xroot;
while (x < 0 && screenx) {
screenx--;
output <<= 1;
output |= ((xroot + travel) & 8) >> 3;
if (!(screenx & 7))
*dst++ = output;
xsumsquares += 2 * x++ + 1;
if (xsumsquares < xnextsquare)
xnextsquare -= 2 * xroot-- - 1;
}
}
// Quadrant IV (bottom right)
if (screenx) {
xnextsquare = (xroot + 1) * (xroot + 1);
while (screenx--) {
output <<= 1;
output |= ((xroot + travel) & 8) >> 3;
if (!(screenx & 7))
*dst++ = output;
xsumsquares += 2 * x++ + 1;
if (xsumsquares >= xnextsquare)
xnextsquare += 2 * ++xroot + 1;
}
}
ysumsquares += 2 * y++ + 1;
if (ysumsquares >= ynextsquare)
ynextsquare += 2 * ++yroot + 1;
screeny--;
}
show();
}
void set_pixel(uint8_t x, uint8_t y, uint8_t mode) {
byte *addr = &fb[x / 8 + y * X_SEGMENTS];
byte mask = 128 >> (x % 8);
switch (mode) {
case 0: // clear pixel
*addr &= ~mask;
break;
case 1: // plot pixel
*addr |= mask;
break;
case 2: // XOR pixel
*addr ^= mask;
break;
}
}
void safe_pixel(uint8_t x, uint8_t y, uint8_t mode) {
if ((x >= X_SEGMENTS * 8) || (y >= Y_SEGMENTS * 8))
return;
set_pixel(x, y, mode);
}
// turn off every LED in the framebuffer
void clear() {
byte *addr = fb;
for (byte i = 0; i < 8 * NUM_SEGMENTS; i++)
*addr++ = 0;
}
// send the raster order framebuffer in the correct order
// for the boustrophedon layout of daisy-chained MAX7219s
void show() {
for (byte row = 0; row < 8; row++) {
digitalWrite(CS, LOW);
byte segment = NUM_SEGMENTS;
while (segment--) {
byte x = segment % X_SEGMENTS;
byte y = segment / X_SEGMENTS * 8;
byte addr = (row + y) * X_SEGMENTS;
if (segment & X_SEGMENTS) { // odd rows of segments
shiftOut(DIN, CLK, MSBFIRST, 8 - row);
shiftOut(DIN, CLK, LSBFIRST, fb[addr + x]);
} else { // even rows of segments
shiftOut(DIN, CLK, MSBFIRST, 1 + row);
shiftOut(DIN, CLK, MSBFIRST, fb[addr - x + X_SEGMENTS - 1]);
}
}
digitalWrite(CS, HIGH);
}
}