Auto"snake" on FastLED matrix

Using Arduino Programming Questions
1

So Ive made a host of animations for a 16 by 16 FastLED matrix. One I want is a "snake" that goes around the screen by itself. The code seems to work however after some time it goes crazy and stops working. I cant find why in the code. Any suggestions... Pixel uses x y coordinates and returns the pixel number btw

  void snake()
  {
    if (snakerunning == false)
    {
      FastLED.clear();
      dir = 0;
      lastdir = 0;
      randomstartx = random(0, 16);
      randomstarty = random(0, 16);
      for (int i = 0; i < SNAKELENGTH; i++)
      { //saving snake posistion in a matrix for later
        snakepixels[i] = pixel(randomstartx, randomstarty + i);
      }
      snakerunning = true;
    }

    int randomtime = random(100, 500);
    int randomtime2 = random(0, 60);
    while (snakerunning == true)
    {
      EVERY_N_MILLISECONDS(100)
      {
        drawsnake();
        switch (dir)
        {
        case 0:
          randomstarty--;
          if (randomstarty < 0)
          {
            randomstarty = 15;
          }
          break;
        case 1:
          randomstarty++;
          if (randomstarty > 15)
          {
            randomstarty = 0;
          }
          break;
        case 2:
          if (randomstartx > 15)
          {
            randomstartx = 0;
          }
          break;
        case 3:
          randomstartx--;
          if (randomstartx < 0)
          {
            randomstartx = 15;
          }
          break;
        }
      }
      EVERY_N_MILLISECONDS(randomtime)
      {
        dir = random(4);
        if (lastdir == 0 || lastdir == 1)
        {
          dir = random(2, 4);
        }
        if (lastdir == 2 || lastdir == 3)
        {
          dir = random(2);
        }
        lastdir = dir;
      }
      EVERY_N_SECONDS(10)
      {
        snakerunning = false;
        FastLED.clear();
        for (int i = 0; i < SNAKELENGTH; i++)
        { //blanking snake pixels for the next run
          snakepixels[i] = 0;
        }
      }
    }
  }
  void drawsnake()
  {
    FastLED.clear();
    for (int i = SNAKELENGTH - 1; i > 0; i--)
    {
      snakepixels[i] = snakepixels[i - 1];
    }
    snakepixels[0] = pixel(randomstartx, randomstarty);
    for (int i = 0; i < SNAKELENGTH; i++)
    {
      leds[snakepixels[i]] = CHSV((255 / SNAKELENGTH) * i, 255, 255);
    }
    FastLED.show();
  }
2

Please post a complete sketch showing how the variables are declared and how the functions are called

My best guess would be that you are writing outside the bounds of an array

3

nothing obvious in that part of the code... Maybe the bug is in the rest of the code, or the power or something you did not share

this case look a bit suspicious compared to the others as you don't modify randomstartx but that would not be the cause for a crash.

4

unconventional. can you post the definition?

5 
        randomstartx = random(0, 16);
        randomstarty = random(0, 16);
        for (int i = 0; i < SNAKELENGTH; i++)
        { //saving snake posistion in a matrix for later
            snakepixels[i] = pixel(randomstartx, randomstarty + i);

if "randomstarty" is 16, is "randomstarty + i" guranteed to be within range of snakepixels?

6

EVERY_N_MILLISECONDS is defined in the FastLED library. It is a preprocessor macro which is replaced by a block of code when compiled.

I think to remember people had issues with the hidden variable it generates. I would advise to use millis() and your own variables...

7

Thanks for this suggestion. It was trying to write outside the array. During the first for loop when I write the values to the snake pixels I didnt allow for when randomstarty+i goes above the size of the array in the y direction. Ive changed that statement now to roll round back to 0.

8

agree. makes it hard to follow
why make it hard for reader to understand what the code is doing?

9

That was the issue, watching the code again it only broke when the snake started at the bottom edge of the matrix. Ive added lines to solve the rollover.

10

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