Help with bitwise operators

Programming Questions

eamonmolo..

in Programming Questions • 8 months ago

PImage P1, P2;
int bg = 0x00;
int fg = 0xFF;
int len1, len2;
void setup()
{
    size(512, 512, P3D);
    noLoop();
    noStroke();
    len1 = (8 * width / 13);
}
void draw()
{
    //Layer 1
    background(bg);
    fill(fg);
    ellipse(width / 3, height / 2, len1, len1);
    P1 = get();
    //Layer 2
    background(bg);
    fill(fg);
    ellipse(2 * width / 3, height / 2, len1, len1);
    P2 = get();
    imageXOR(P1, P2);
    image(P1,0,0);
}
void imageXOR(PImage I1, PImage I2)
{
    for (int i = 0; i < min(I1.width, I2.width); i++)
        for (int j = 0; j < min(I1.height, I2.height); j++)
            I1.set(i, j, I1.get(i, j) ^ I2.get(i, j));
}

I have this book teaching me processing and it has this section on bitwise operators, but I can't get any of them to work correctly. Here is the XOR one, for example. The expected output is on the following image:

But the actual output is:

I have copied everything correctly, as far as I can tell. Processing 2.0b7. I can include the other examples' (namely AND and OR) images if things aren't clear enough. Thanks in advance.

Replies(6)

GoToLoop

Re: Help with bitwise operators

8 months ago

I'm still only use current stable Processing v1.5.1.
And it worked alright to me here as seen in that book's picture!

PhiLho

Re: Help with bitwise operators

8 months ago

For 2.0b7, just remove the , P3D part. It isn't necessary for this sketch, and the demo doesn't work with OpenGL, obviously.

return_tr..

Re: Help with bitwise operators

8 months ago

I also have a question about bitwise comparison. It does not seem to work right.

example from my script:
...

final static int is_visible = unhex("00000001");
final static int is_enabled = unhex("00000002");
final static int is_checked = unhex("00000004");
final static int is_seperated = unhex("00000008");

...so bitwise these would look like "0001", "0010", "0100" and "1000"
later i want to construct a class and set those flags from an user-defined addition of these flags
looks and should work like this:

class MenuItemClass {
String Caption;
int Parent;
int Sibling;
boolean Visible; // is this to draw at all?
boolean Enabled; // clickable?
boolean Checked; // has a checkmark?
boolean Seperated; // followed by a seperator-line?
boolean Expanded; // can not set in advance!
MenuItemClass(String _caption, int _childOf, int _siblingOf, int _Flags) {
this.Caption = _caption;
this.Parent = _childOf;
this.Sibling = _siblingOf;
this.Visible = _Flags && is_visible;
this.Enabled = _Flags && is_enabled;
this.Checked = _Flags && is_checked;
// etc...
}
}

the problem now is: If I use "&&" to compare it complains

"The operator && is undefined for the argument type(s) int, int"

even if I do all the comparison within seperate if-statements, write the equation in parens, plus leading "boolean" or whatever. I tried all combinations you can think of and since I'm out of ideas I have to ask you.

If I use just "&" it also does not compare but would add bitwise and then it complains the same but about type(s) boolean!

What is the locig AND to find out if a certain bit in any variable expression at will is set ?

Please don't tell me to set them values up seperately - l'lI need this comparison for many other purposes as well.

kooogy

Re: Re: Help with bitwise operators

8 months ago

what you wrote would be good in C or C++ where 0 is treated as true. but not in java. you are trying to assign an int to a boolean.

try

this.visible = (_Flags & is_visible) != 0;

i'd also ditch the unhex() and just use 0x00001; etc at the top

return_tr..

Re: Help with bitwise operators

8 months ago

thanx kooogy,

at least it runs without complains now. test for full functionality has to wait until some more typing is done.

also thanx for the hint with 0x00, this I couldn't find in the help, there's just described hex() and unhex() but not how to write the numbers. I tried &HFF, $HFF $FF and all other usual stuff already which resulted in frustration and rage - both should be added to the help somehow.

GoToLoop

Re: Help with bitwise operators

8 months ago

What you wrote would be good in C or C++ where 0 is treated as true.

I guess you meant any value non zero is considered true!

The logical operators -> ||, &&, !
can only be used on boolean values.

Now some of the bitwise operators, like for example -> |, &, ^
are overloaded both for general integers and booleans!

It means you can use them in place of logical operators for logical purposes!
And of course, to do bit math!
Although you can't mix both types as operands!

Even more, bitwise operators are faster than logical ones!!!
However, logical ones are preferred when the operands themselves are "heavy",
like long maths and method calls, etc.

Logical ones are lazily evaluated and has lower order of precedence.
And contrariwise, bitwise are eager and has higher precedence.

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