TTGO IMU Starfield demo

// by Ido Gendel, 2021
// Using the Arduino IDE with ESP32 board support installed, and the TTGO TWatch libraries
// (See https://github.com/Xinyuan-LilyGO/TTGO_TWatch_Library)
// Share and enjoy!

#define LILYGO_WATCH_2020_V1
#include <LilyGoWatch.h>

#define STARS 120U
#define STAR_SIZE 3U

TTGOClass *watch;

struct tStar {

  int16_t x, y;
  uint16_t z;
  int32_t ix, iy;
  int32_t shade;

} star[STARS];

//=========================================================
void initStars(void) {

  uint32_t n;

  for (n = 0; n < STARS; n++) {

    star[n].x = random(65536);
    star[n].y = random(65536);
    star[n].z = random(65536);
    star[n].shade = random(2);

  }

}

//=========================================================
void moveStars(void) {

  uint32_t n, sBase;
  int32_t ax, ay, az;
  float factor;

  Accel acc;

  watch->bma->getAccel(acc);
  ax = acc.x >> 2;
  ay = acc.y >> 2;
  az = acc.z >> 3;

  // Erase and draw each one in turn, to avoid flicker
  for (n = 0; n < STARS; n++) {

    watch->tft->fillRect(star[n].ix, star[n].iy, STAR_SIZE, STAR_SIZE, 0);

    // 5-bit brightness value; screen uses 565 color scheme
    sBase = (256 - (star[n].z >> 8)) >> 3;
    star[n].x += ax;
    star[n].y += ay;
    star[n].z -= az;
    // Avoid potential division-by-zero
    if (0 == star[n].z) star[n].z = 1;

    factor = 240.0 / (float)star[n].z;
    star[n].ix = int((float)(star[n].x) * factor) + 120;
    star[n].iy = int((float)(star[n].y) * factor) + 120;

    watch->tft->fillRect(star[n].ix, star[n].iy, STAR_SIZE, STAR_SIZE,
                         star[n].shade ? sBase : (sBase * 2113));

  }

}

//=========================================================
void setup() {

    watch = TTGOClass::getWatch();
    watch->begin();
    watch->openBL();
    watch->bma->begin();
    watch->bma->enableAccel();

    initStars();

}

//=========================================================
void loop() {
  moveStars();
}