How to fill-in a diamond without PAINT

[OldMoses]

I have no idea what "bit shifting" means, except that the Wiki page says it divides it by 2 faster. Oh well, I try not to use things I don't understand unless I have to. But still interesting!

I don't think many people use bit shifting that often, it is a tad incomprehensible, and it's really only useful where there's an integer with an even power of two. It just happened to be ok for a diamond with a size of 20.

_SHR(variable%, x%) will divide variable% by 2 ^ x%, dropping fractions
_SHL (variable%, x%) will multiply variable% by 2 ^ x%,

I do it just to get used to it, really, for the eventual day where it actually might save some processor time in a fast application. It doesn't do well for precision division because, like an integer, it drops fractional results since it won't preserve overflow bits. I like it for dividing a screen into halves, quarters, eighths, etc., or for converting between LOCATE positions and _PRINTSTRING positions. In those cases one pixel one way or the other doesn't make a big difference on most screens and there isn't a half pixel anyway. You don't need it for most stuff, but it's cool to know it.

Example:
a% = 15 '                            in binary that's a% = &B0000000000001111   (big endian form here for clarity)

b% = _SHL(a%, 1) '            shifting a% one bit to the left, b% = &B0000000000011110  or b% = 30

c% = _SHR(a%, 1) '            shifting a% one bit to the right, c% = &B0000000000000111 or c% = 7

If you shift around a lot without care, you lose precision quickly, for example:

Code: (Select All)

a% = 15
PRINT a%
b% = _SHR(a%, 1)
PRINT b%
c% = _SHL(b%, 1)
PRINT c%

If I want to put something a quarter of the way across a screen width I would do _SHR(_WIDTH(0), 2) for an X position, which is the same as  _WIDTH(0) / 4