This image was made in a special way. Using the command line tool xdotool, which can control the mouse and keyboard, I made each spiralpoly using this command
x=0;y=0;xdotool mousemove --polar $x $y ; xdotool mousedown 1 ; while $y -lt 400 ; do xdotool mousemove --polar $x $y ; x=$( echo "scale=0;$x+1+$y*2" | bc );y=$(($y+1)); sleep 0.001; done ; xdotool mouseup 1
While putting the Gimp Image window in the center of the screen for each one. In Gimp, I configured the paintbrush to fade out over 32767 pixels and to use the color from gradient over 20000 pixels. Each SpiralPoly uses one of Gimp's default gradients. Brush size = 2.