Detour: Arduino Benchmark with Mandelbrot

A project log for VGA Shield Wing

A VGA Arduino Uno Shield or Adafruit Feather Wing 640x480 - 512 colours

magicwolfiMagicWolfi 09/26/2021 at 15:470 Comments

With a display and a bunch of different Arduino/Feather boards, I figured it would be a fun little exercise to see how fast those boards would render a Mandelbrot set image with my video shield. Contestants are Arduino Uno, Mega, Due and a Feather M4 Express in NTSC320x200 and PAL300x240 resolutions. Calculations are done in float numbers for the standard number range of -2.5<x<+1 and -1<y<1. Results are rounded to the next full 0.1 second.

BoardNTSC 320x200
PAL 300x240

And here is a bad quality demo picture of the resulting image.

The code is not optimized for speed, I have read about implementation that use only 3 multiplications instead of 6. Work for the future.

// Draw a Apfelmaennchen
void Mandelbrot (byte channel, float Xn, float Xp, float Yn, float Yp){
	float x0, y0, xtemp;
	float x = 0;
	float y = 0;
	u_int16 Px, Py;
	u_int16 iteration = 0;
	u_int16 max_iteration = 256;
	for (Py = 0; Py < YPIXELS; Py++){
		y0 = (Yp - Yn)/YPIXELS*Py + Yn;
		for (Px = 0; Px < XPIXELS; Px++){
			x0 = (Xp - Xn)/XPIXELS*Px + Xn;
			x = 0;
			y = 0;
			iteration = 0;
			while ((x*x + y*y <= 2*2) && (iteration < max_iteration) ) {
				xtemp = x*x - y*y + x0;
				y = 2*x*y + y0;
				x = xtemp;
			P42Display.SetYUVPixel (channel, Px, Py, (byte) (iteration&0xff) +0x20);