PVector Array weirdness

Programming Questions

harveymoon

in Programming Questions • 2 years ago

I am super confused. I am trying to append a PVector onto a PVector array and the array function does not work. Neither does expand or shorten either.

heres some code for thought. thanks

PVector[] theLine; //PVector array
PVector current;
void setup(){
size(200,200);
theLine = new PVector[5]; //five blank spots to start
current = new PVector();
}
void draw(){
current.x =mouseX; //assign current to mouse locaiton
current.y = mouseY;
append(theLine, current); //This doesn't seem to do anything but it should, right?
expand(theLine,10); // this doesn't work either
shorten(theLine); // or even this. Something must be totally wrong
println(current.x + ", " + current.y); // print the mouse location
println(theLine); // print out the entire array (always prints 4 null)
}

Replies(7)

monkstone

I think you might want some element of control over when the data updates if you have an empty draw(){} then you can use mouseReleased keyPressed events to control your sketch (also why not directly assign the mouseX and mouseY to the new PVector() that you should be using to store the current mouse position). Here is a proposed mouse released:-

void mouseReleased() {

current = new PVector(mouseX, mouseY);

append(theLine, current);

println(current);

}

blindfish

Re: PVector Array weirdness

2 years ago

Note the point made in the Reference regarding using these array methods with objects:

When using an array of objects, the data returned from the function must be cast to the object array's data type. For example: SomeClass[] items = (SomeClass[]) append(originalArray, element).

You're also not explicitly assigning the result back to theLine[]

theLine = (PVector[]) append(theLine, current);

I'm not sure what you're trying to achieve, but your code isn't really going to 'work' anyway (at best it will sort of work but be hopelessly innefficient): note that append(), not surprisingly, adds an element to the end of the array. Unfortunately shorten() removes the last element of the array, whereas I expect you were hoping it would take the first. That means you're potentially adding then removing the same element from the array... Though your use of expand() will actually avoid you losing the data you appended you will land up with a huge number of null values in your array, and very few elements containing data...

When working with objects you're actually much better off using an ArrayList for storage rather than a standard array. The add() and remove() methods allow you to specify which element to act on and you don't need to declare a size...

harveymoon

Re: Re: PVector Array weirdness

2 years ago

I didn't know that you had to write it as theLine = (PVector[]) this solves my problem, thanks.

I'm not sure what you're trying to achieve, but your code isn't really going to 'work' anyway (at best it will sort of work but be hopelessly innefficient): note that append(), not surprisingly, adds an element to the end of the array. Unfortunately shorten() removes the last element of the array, whereas I expect you were hoping it would take the first. That means you're potentially adding then removing the same element from the array... Though your use of expand() will actually avoid you losing the data you appended you will land up with a huge number of null values in your array, and very few elements containing data...

This code sample was not designed to do anything. I wrote it for this post as a simple explanation of my problem.

the expand and shorten were not intended to be used at all, I included them to show that they don't work either. I initally wrote it without the expand and shorten included. It was intended to add a new value to the PVector array theLine each loop. the MouseX and Y were just there to have new+different values.

harveymoon

Re: PVector Array weirdness

2 years ago

ok, My problem now is that the array changes every value each time.

PVector[] theLine; //PVector array
PVector current;
void setup(){
size(200,200);
theLine = new PVector[]
{
new PVector(0,5),
new PVector(6,6,6)
};
current = new PVector();
}
void mousePressed(){
current.x =mouseX; //assign current to mouse locaiton
current.y = mouseY;
theLine = (PVector[]) append(theLine, current); }
void draw(){
println(current.x + ", " + current.y); // print the mouse location
println(theLine); // print out the entire array
}

What prints out looks correct. except that each time, instead of just adding a new number onto the array, it changes the previous. You can notice that the first number remains constant. it only changes the numbers that it has created.

PhiLho

Re: PVector Array weirdness

2 years ago

The error is that you reuse current, the same PVector. So you fill the array with references to this PVector, and when you change a value in this PVector, all the references are updated at the same time. You have to create and add a new PVector each time.

harveymoon

Re: PVector Array weirdness

2 years ago

cool, so I ended up doing this, and it works.

theLine = (PVector[]) append(theLine, new PVector(mouseX,mouseY));

I imagine that I could also do something like this

theLine = (PVector[]) append(theLine, new PVector(Current.x,Current.y));

is that true?

thanks

PhiLho

Re: PVector Array weirdness

2 years ago

Yes. You might also be interested by ArrayList.

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