Processing 1.0 - Processing Discourse - append (arrays) can't catch up?

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append (arrays) can't catch up? (Read 2455 times)

BEnm

append (arrays) can't catch up?
Sep 18^th, 2007, 11:37pm

Hi,

I wrote some simple code, which allows you to draw with the mouse. I store the mouse coordinates in arrays because I'd like to do some stuff with that info later..
But, somehow if you draw fast the lines are disrupted. I probably has something to do with an inefficient way of storing these coordinates? (;too heavy demands on memory, or somethin'?)

Here's my Code:

Line lines;

void setup() {

size(600, 300);
background(255);

lines = new Line();

}

void draw() {
lines.drawLine();
}

class Line {

int[] xCoordinates = new int[0];
int[] yCoordinates = new int[0];
int index = -1;

Line() {

}

void appendLineProps(int x, int y) {
xCoordinates = append(xCoordinates, x);
yCoordinates = append(yCoordinates, y);
index++;
}

void drawLine() {
if(index > 1) {
if(xCoordinates[(index-1)] != -1 && xCoordinates[index] != -1) {
line(xCoordinates[(index-1)], yCoordinates[(index-1)], xCoordinates[index], yCoordinates[index]);
}
}
}

}

void mouseReleased() {
lines.appendLineProps(-1, -1);
}

void mouseDragged() {
lines.appendLineProps(mouseX, mouseY);
}

I appreciate your help,

BEnm

JohnG Ex Member	Re: append (arrays) can't catch up? Reply #1 - Sep 18^th, 2007, 11:47pm Unfortunately append gets slower the larger the array you're adding to. One option is to create a large empty array initially, and have a "lastPoint" int which points to the latest entry in the array. Then if you fill that array, double the size of it, and carry on as before.

BEnm Ex Member	Re: append (arrays) can't catch up? Reply #2 - Sep 19^th, 2007, 12:02am Hi JohnG, thanks for the help. Do you know some nice resources of information about the behind-the-scenes stuff with arrays? e.g. I also wonder whether replacing an array - declaring one with the same name (twice as long) - really replaces it, and not only its name; that both keep consuming memory.. thanks

JohnG

Re: append (arrays) can't catch up?
Reply #3 - Sep 19^th, 2007, 12:20am

The behind the scenes problem is that append created new array of size original+1, then copies the contents of the original intot he new one, and adds the new item as the last entry.

As you can see, doing this each and every frame isn't very quick.

As for the replacing of it, doing:
Code:

int[] foo=new int[10];
foo=new int[11];

Doesn't delete the original foo, it does however mark it for deletion by the garbage collector, and it will eventually be removed when Java needs some space.

mflux

Re: append (arrays) can't catch up?
Reply #4 - Sep 19^th, 2007, 7:24am

JohnG

Wouldn't you rather just recommend ArrayList?

I wouldn't recommend getting way too comfortable with these
http://java.sun.com/j2se/1.4.2/docs/api/java/util/ArrayList.html

However they are very very useful and does all the behind the scenes stuff for you, as JohnG described.

I've actually written my own ArrayList-like array class, but Java's is still faster.

Portfolio

JohnG Ex Member	Re: append (arrays) can't catch up? Reply #5 - Sep 19^th, 2007, 9:58am I would for many cases, but for storing/retrieving ints regularly, I wouldn't, since they have to be boxed/unboxed to/from Integer each and every time you read/write to the ArrayList.

fry YaBB Moderator Offline Posts: 2623 mass, usa	Re: append (arrays) can't catch up? Reply #6 - Sep 19^th, 2007, 1:47pm the fastest when dealing with an array of ints or floats is to use expand(), an example is in this thread: http://processing.org/discourse/yabb_beta/YaBB.cgi?board=Syntax;action=display;num=1187580155

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