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Index › Programming Questions & Help › Syntax Questions › passing PVectors

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passing PVectors (Read 470 times)

jf-27

passing PVectors
Aug 8^th, 2009, 12:04pm

Hey quick question, but is there a specific way to pass PVectors to a function?

This sounds like a really easy question, but when I have code that essentially looks like this:

Code:


PVector vect1 = new PVector(2,2,2);

setup() {
  something here...
}

draw() {
  calc(vect1);
}

void calc(PVector v1) {
  v1.normalize();
}

I am having the problem that the passed global vector (in this case vect1) will be normalized! I do not want this to happen, is there a way to do this other than defining a new PVector, setting it to vect1, and then passing that PVector instead?

I had always thought that passing a variable will mean that the function would only get the value of the variable, not the actual variable itself

PhiLho

Re: passing PVectors
Reply #1 - Aug 8^th, 2009, 2:34pm

If you pass a primitive type (int, float...), changing it won't change the original value.
Likewise, you cannot change the passed object (ie. if you do v1 = new PVector(), vect1 won't be changed) because that's just a reference (pointer) to some data structure, but the content of objects can be changed (the structure content).
So you guessed right, you have to copy the PVector if you don't want side effects.

Jo Wood

Re: passing PVectors
Reply #2 - Aug 12^th, 2009, 5:22am

PhiLho is correct (and arrays are also passed by reference not value). But note that PVector has a few static and other methods that do not affect the value of the input vector. For example you can get normalize() to create a new vector leaving the original intact:

Quote:

PVector vect1 = new PVector(2,2,2);

void setup() {
  // Do something here
  noLoop();
}

void draw() {
  PVector v2 = calc(vect1);
  println("Vect 1 is "+vect1+ " v2 is "+v2);
}

PVector calc(PVector v1) {
  return v1.normalize(null);
}

See the PVector developer's reference for full details.

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