@Jessy:
If you're using the smooth iteration DE then there is a faster method - basically Buddhi's suggestion here:
http://www.fractalforums.com/theory/a-new-simple-way-to-compute-de-for-any-trig-mandelbulb/msg11047/#msg11047I've used it with the same method as the smooth iteration version i.e. get the final magnitude at step and at step+delta then use:
dir = magn1 - magn
DE = 0.3*@delta*sqrt(abs(@mpwr-1.0)))*magn*log(magn)/abs(dir)
I use changes in the sign of dir (from positive to negative) to check for "missed solid" when the option is enabled.
magn1-magn being zero needs testing for - in which case use a preset step distance (checked against the array if using that method)
I got the 0.3 by trial and error and I use:
step = DE*(0.6/ @accuracy)
An @accuracy of 1 is fast but prone to errors and a value of 2 rarely produces errors.
Note the sqrt(abs(@mpwr-1.0)) - I found that using this makes it consistent using different powers in exactly the same way as it did for me using the analytical method.
I think it's faster because it only requires one log() call whereas the smooth iteration method needs at least 4, though it could be that in general the calculated distances are more accurate (but I doubt it)
If wanting to use smooth iteration for the colouring you now only need to calculate the value when solid is actually found.