Nice effect, I don't really much you can do to improve on it, because improvements are usually found in the main code the only thing I spotted was this:
midx=pw/2
midy=ph/2
which can be changed to:
midx=pw shr 1
midy=ph shr 1
bit shifting is faster than using / and *
another thing is (and this won't get you faster code) is that this:
For pixel.pixel = Each pixel
Delete pixel
Next
can be done like this:
delete each pixel
that will do the same thing and is easier.
midx=pw/2
midy=ph/2
which can be changed to:
midx=pw shr 1
midy=ph shr 1
bit shifting is faster than using / and *
another thing is (and this won't get you faster code) is that this:
For pixel.pixel = Each pixel
Delete pixel
Next
can be done like this:
delete each pixel
that will do the same thing and is easier.