Copy one PVector into another?

bob97086

I have a little exposure to Java and Processing. My simple-minded, self-teaching project generates a curve by linking line segments. The end points are PVectors v1 and v2. The final end point of one segment (v2) becomes the initial end point (v1) of the next. So in setup(), I define (x,y) values for v1 then, in draw(), I define a different (x,y) pair for v2 and call line() using v1 and v2. The obvious next step is to copy v2 into v1 in preparation for creating a new v2 in the next draw() loop.

But there's the problem. In the first pass through draw(), the simple statement "v1 = v2;" doesn't copy values but seems to copy the instance address from v2 into v1. I see all the methods for PVector in the Processing Reference but no ".copy()". I don't know if my ignorance is mostly Java or mostly Processing! If this were C++ I would expect a copy() operator to be defined for PVector instances.

Thanks for input to my question.

asimes

A solution could be v1.x = v2.x and v1.y = v2.y

amnon

See: http://www.processing.org/reference/PVector.html

You can use .get()

Although it may be better to just re-use the PVector as it's the same coordinate right? If you use a begin-endShape with (curve)vertex, you don't need to call them twice anyway.

colouredmirrorball

(see above)

quark

The best way would be simply to use the object references.

This may not be exactly what you are looking for but it draws a line from an array of PVectors and leaves the array elements unchanged which is useful.

PVector pa = array[0], pb;
for(int v = 1; v< array.length; v++){
  pb = array[v];
  line(pa.x, pa.y, pb.x, pb.);
  pa = pb;
}

GoToLoop

Best way to transfer the values of a PVector to another 1 is via its set() method:
http://processing.org/reference/PVector_set_.html

// forum.processing.org/two/discussion/7555/
// copy-one-pvector-into-another

PVector v1 = PVector.random2D(this);
println("v1: " + v1);

PVector v2 = new PVector();
v2.set(v1); // Transfer v1's x, y & z values to v2's.
println("v2: " + v2 + "\n"); // Same values.

// Also useful to reset a PVector to specific values:
v2.set(PI, RAD_TO_DEG, DEG_TO_RAD);
println("v1: " + v1); // v1 kept its values. Proof that v2
println("v2: " + v2); // isn't the same alias/object as v1.

exit();

GoToLoop

If this were C++ I would expect a copy() operator to be defined for PVector instances.

Java, like regular C & JS, doesn't have custom operator overloading. Only few built-in 1s like +, &, |, ^. 8-X
The assignment operator = only transfers the result from right to the variable from left:
http://processing.org/reference/assign.html
Its behavior can't be changed/overloaded to something else like C++ & Python can do! [-X

GoToLoop

Some examples which rely on set() in order to avoid needless PVector instantiations:

• http://studio.processingtogether.com/sp/pad/export/ro.90vdKMfkiO$zf/latest
• http://studio.processingtogether.com/sp/pad/export/ro.9NwgKBhS$Gxju/latest
• http://studio.processingtogether.com/sp/pad/export/ro.9D4K1FIWJ7Kxc/latest
• http://forum.processing.org/two/discussion/2829/fifo-queue-problem-with-code#Item_2

bob97086

Thanks all for the helpful responses. The little program did run as expected by separately setting the .x and .y components, but I was looking for a familiar method to assign PVectors. Thanks esp. to GoToLoop. I've glanced at those examples and one will lead to a more satisfying method.