Fast way to check if any object of a class is located at a point.

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kjhenner

Fast way to check if any object of a class is located at a point.

in Programming Questions • 2 years ago

I'm pretty new to java/processing and am trying to make a sort of cellular simulation. I have a bunch of white dots (pigs) that move around the screen and reproduce whenever they "eat" yellow dots (lemons). I've gotten the pigs to be pretty smart at finding lemons (they check each of 9 pixels around them to see which has the highest "lemon gravity," and move to that point.) The problem at this point is framerate. I have two functions that look through an ArrayList and check the location of every object to see if a pig is standing on a lemon or if a prospective movement space is already occupied. There must be a better way to do this! I've tried the following as a (probably silly) workaround, but the println always returns the background color and the boolean never comes up true. Any other ideas?

boolean isLemon(float ilemonx, float ilemony)
{
boolean isLemon = false;
float lemonx, lemony;
lemonx = ilemonx;
lemony = ilemony;
PVector checkLoc;
loadPixels();
color lemonColor = get(int(lemonx), int(lemony));
checkLoc = new PVector(lemonx, lemony);
println(red(lemonColor));
if(red(lemonColor) >= 254 && green(lemonColor) >= 254 && blue(lemonColor) <= 250)
{
isLemon = true;
myFeeder.eat(lemonx, lemony);
}
return isLemon;
}

Replies(4)

PhiLho

Re: Fast way to check if any object of a class is located at a point.

2 years ago

I understand nothing about your code. Since you say you are new to this, I will analyze it in detail.
// How do you call this? For each pixel?
boolean isLemon(float ilemonx, float ilemony)
{
    boolean isLemon = false;
    // You can declare and assign at teh same time.
    // But I don't see the point of making two variables identical to the parameters, they are redundant
    float lemonx, lemony;
    lemonx = ilemonx;
    lemony = ilemony;
    PVector checkLoc;
    // Don't load pixels on each pixel, if that's how you call the function!
    loadPixels();
    // The point of loadPixels is to avoid the usage of get()...
    color lemonColor = get(int(lemonx), int(lemony));
    // You don't seem to use this one...
    checkLoc = new PVector(lemonx, lemony);
    println(red(lemonColor));
    // OK, I suppose
    if(red(lemonColor) >= 254 && green(lemonColor) >= 254 && blue(lemonColor) <= 250)
    {
      isLemon = true;
      myFeeder.eat(lemonx, lemony);
    }
    return isLemon;
}

Beside " I have two functions that look through an ArrayList". Why two functions? How they differ? Why did you switched to pixel inspection?
We don't have enough information on your code...

kjhenner

Re: Re: Fast way to check if any object of a class is located at a point.

2 years ago

Thanks for the tips on code hygiene. I've just been teaching myself based on what works, so there's probably a ton of stuff I'm doing sloppily and/or unnecessarily.

I call the isLemon code each frame for each pig to see if it is standing on a lemon.

The "two functions that look through an ArrayList" both look more or less like this. There is one for checking if there is a lemon at a point and one for checking if there is a pig at a point, but they both use basically the same method. Because the number of times these are called increases exponentially, they seem likely suspects for low framerates.

boolean isLemon(float ix, float iy)
{
    PVector lemLoc;
    PVector checkLoc;
    boolean isLemon;
    isLemon = false;
    checkLoc = new PVector(ix, iy);
    for(int i=0;i<lemons.size();i++) {
      lemon meyer = (lemon) lemons.get(i);
      lemLoc = meyer.getLoc();
      if((round(checkLoc.x) == round(lemLoc.x)) && (round(checkLoc.y) == round(lemLoc.y)))
      {
        isLemon = true;
        myFeeder.eat(lemLoc.x, lemLoc.y);
      }
    }
    return isLemon;
}

I was thinking about this more and realized it would probably be faster to just use a 2d boolean array to track the locations of all pigs and lemons. Hope I answered my own question...

PhiLho

Re: Fast way to check if any object of a class is located at a point.

2 years ago

You can avoid creating checkLoc, just use ix and iy directly. Object creation is still quite costly in a loop.
Otherwise, for checking collision of lot of objects against lot of other objects, there are techniques called quadtree (seach in Wikipedia), but I haven't really used them.

kjhenner

Re: Re: Fast way to check if any object of a class is located at a point.

2 years ago

Thanks, quadtree looks pretty cool. For now, the 2d array I set up is making things way faster, so I'll probably use that for now, but now I know where to turn if things start slowing down again.

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