[bmx] Bit Flags by rdodson41 [ 1+ years ago ]

[BlitzBot]

Title : Bit Flags
Author : rdodson41
Posted : 1+ years ago

Description : Bit flags are can be used to set parameters for a function. The value that is inputed as a parameter when calling the function is an integer, which is the sum of all the bits of parameters you want. For example:

In the B+ function create window, there are many different style flags you can have. You pick which styles you want, and add up there bit values. This is the integer that is used as the flag. The default is 15, which would mean the window has a title bar, is resizable, has a menu, and has a status bar.

This is useful for many things, so have fun with it!

Code :

Code (blitzmax) Select Expand

Repeat
Print
flag=Int(Input$("Flag:>"))
bit=Int(Input$("Bit:>"))
Select bitflag(flag,bit)
Case 0
Print "Bit "+bit+" has not been found in flag "+flag+"."
Case 1
Print "Bit "+bit+" has been found in flag "+flag+"."
End Select
Forever



Function bitflag(flag,bit)
p=0
Repeat
If 2^p>11 Then Exit
p:+1
Forever
p:-1
For i=p To 0 Step -1
If flag-(2^i)>=0 Then
flag:-(2^i)
If 2^i=bit Then Return 1
End If
Next
Return 0
End Function

Comments :


Koriolis(Posted 1+ years ago)

 There is far more simple:

Code Select Expand

Function bitflag(flag,bit)
Return (flag Shr bit) And 1
End FunctionNote: in this version 'bit' starts at 0, not 1 (if you want it 1 base just do "Return (flag Shr (bit-1)) And 1")


rdodson41(Posted 1+ years ago)

 Oh, huh... and i spent and hour trying to figure this one out...


rdodson41(Posted 1+ years ago)

 It would be this:

Code Select Expand

Function BitFlag(flag,bit)
Return (flag & bit)=bit
End Function
Unfortunatly 'And' is only a logical opperater, not a bitwise opperator. So you have to use the & symbol.


Techlord(Posted 1+ years ago)

 A working Example.

Code Select Expand

;flags (multiple of 2)
fullbright=1
vertexcolors=2
flatshaded=4
disablefog=8
disablebackfaceculling=16
forcealphablending=32

;assignment
fx=fullbright+vertexcolors+disablefog

Print("fx="+fx+":")

;evaluate; use '/' and If's only.
If fx/fullbright And 1 Print("fullbright") ;do stuff
If fx/vertexcolors And 1  Print("vertexcolors")
If fx/flatshaded And 1 Print("flatshaded")
If fx/disablefog And 1 Print("disablefog")
If fx/disablebackfaceculling And 1 Print("disablebackfaceculling")
If fx/forcealphablending And 1 Print("forcealphablending")