Snake game on rgb led matrix

The apple-eating animation is a hollow circle that grows from the point of the apple and fades its colour out on each step.
I added a helper function to draw the circle that was fast enough not to affect the frame rate. I don't know much C but I can try port it to be used in the Espruino graphic library.

  m.drawCircle = function(posX, posY, radX){
    var radY = 0;
    // Decision criterion divided by 2 evaluated at radX=radX, radY=0 .
    var decisionOver2 = 1 - radX;
  
    while (radX >= radY) {
      m.setPixel(radX + posX,  radY + posY);
      m.setPixel(radY + posX,  radX + posY);
      m.setPixel(-radX + posX,  radY + posY);
      m.setPixel(-radY + posX,  radX + posY);
      m.setPixel(-radX + posX, -radY + posY);
      m.setPixel(-radY + posX, -radX + posY);
      m.setPixel(radX + posX, -radY + posY);
      m.setPixel(radY + posX, -radX + posY);
      radY++;
  
      if (decisionOver2 <= 0) {
        // Change in decision criterion for radY -> radY+1 .
        decisionOver2 += 2 * radY + 1;
      }
      else {
        radX--;
        // Change for radY -> radY+1, radX -> radX-1 .
        decisionOver2 += 2 * (radY - radX) + 1;
      }
    }
  };