This should be a simple one. I am trying to rewrite this MouseCallback function. It is a Gluts MouseCallback function not that it matters i guess. I ran across a set of statements which im pretty sure are conditoinal statements. but i have never seen this kind of set up for a conditional statement before.

  mouseLClickButton |= (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN);
  mouseRClickButton |= (button == GLUT_RIGHT_BUTTON && state == GLUT_DOWN);
  mouseMClickButton |= (button == GLUT_MIDDLE_BUTTON && state == GLUT_DOWN);

  mouseLClickButton &= !(button == GLUT_LEFT_BUTTON && state == GLUT_UP);
  mouseRClickButton &= !(button == GLUT_RIGHT_BUTTON && state == GLUT_UP);
  mouseMClickButton &= !(button == GLUT_MIDDLE_BUTTON && state == GLUT_UP);

can some one explain what the first set of operators are saying. |= and &=

im assuming that the first three are conditional statements for individual button presses and the second three are for multiple button presses. But i would just like an explanation of what exactly is going on here with the syntax. I have never seen anything like that.

mouseClickButton are all bools. im guessing that if the contitional statement on the right of the operator is tru then it makes that bool on the left tru but its just kind of confusing to me.

This is interesting. I did a little digging and found the following. They are apparently called (bitwise OR assignment) and (bitwise AND assignment),

http://en.wikipedia.org/wiki/Operators_in_C_and_C%2B%2B

Here are two more pages that I found using the 'english' names

http://msdn.microsoft.com/en-us/library/ie/81bads72%28v=vs.94%29.aspx

http://msdn.microsoft.com/en-us/library/vstudio/k6d7hcca%28v=vs.100%29.aspx

Hopefully someone around here can explain how they apply to GLUT controls.

EDIT: Oh wait here we go... It looks like your suspicions were correct about this allowing for simultaneous presses.

http://www.lighthouse3d.com/opengl/glut/index.php3?5

It's bitwise logic operators being used the same way that you can use the addition operator to say +=.

That is:

a |= b

is the same as:

a = a | b

Seeing the |= at the top there, I'd imagine that those variables are being given a value prior to what you posted. Since boolean values are either true or zero, these operations can be used as standard logic operators in the case that they're working on boolean values (in this case they are). You'd need to be careful with &= in cases where you're not using boolean inputs, since you can have two nonzero values that would be true for && but not for &.

The idea is that you can break up complex conditionals:

if(((a && b) || (c && d) || (x && y && z)) {
  //stuff
}

versus

bool condition = a && b;
condition |= c && d;
condition |= x && y && z;
if(condition) {
  //stuff
}

If this confuses you, do some research on bitwise logic and truth tables for and/or/xor. It should start to make sense once you have all the information.

That's weird though... since the right part is only a true or false expression, it could be written as

BOOL mouseLClickButton = (button == GLUT_LEFT_BUTTON && state == GLUT_DOWN);

so im assuming mouseLClickButton are integer, which is ratter poor design choice imo.

Or it might be a bool and wanted to get rid of warning or error messages, being too lazy to cast...

Edit: i just saw the &= afterward. Still, this code look weird somehow.

I think i am understanding. mouseClickButton is in fact a bool and is actually never initialized until these conditional statements.

I am following what you say there frob but I am not understanding this a=a&b or a=a|b .

Is this (a=a&b) saying a is true if both a AND b are true?

and this (a=a|b) is saying a is true if a OR b is true?

I think i am understanding. mouseClickButton is in fact a bool and is actually never initialized until these conditional statements.

I am following what you say there frob but I am not understanding this a=a&b or a=a|b .

Is this (a=a&b) saying a is true if both a AND b are true?

and this (a=a|b) is saying a is true if a OR b is true?

Nope. Bitwise operations operate on bits.

For example, a |= b means effectively

for i from 0 to number of bits in a:
  if bit i of b is set, set the bit i of a
  otherwise leave the bit i of a unchanged

Similarly for the AND operation.

Alvaro, your example makes my eyes feel much better. And SiCrane thank you very much for your explanation.

Bregma is this diagram similar to your explanation of a|=b?

result = result | expression;

0101    (result)
1100    (expression)
----
1101    (output)