Open Terragen 2, visit heightfield generate 01(if you still have it in your default file, if not, make one...).
Click on 'generate now'. The generator will begin to climb towards 100%... Take your mouse cursor (whilst this generation process is happening) and wiggle it back and forward over the 3D preview window, maybe it's just me but when I do this on my computer the speed of the building process significantly quickens up, stop wiggling the cursor and the speed returns to normal. Does this happen with everyone? ...