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expand array (Read 623 times)
brin
expand array
Sep 23rd, 2006, 11:33pm  
Hello again,

I wrote this:

Code:

int ex;
int timer = 0;//60 or smaller --> outofbounds; 61 --> nullpointer
BG bg[] = new BG [frameCount]; 

void setup()
{
  size(400,400);
  background(255);
  bg = new BG[frameCount];
  
   framerate(30);
  
  
  }
  
void draw()
  { 
  //int timer = 0;
  timer++;
  drawBG();
  circle();
  }
  
     void circle()
    {    
	noStroke();
	fill(0,255,0);
	ellipse(ex,width/2,10,10);  
	ex++;
	}

	
    void drawBG()
{
 // timer++;
    bg[timer].copyBG();
    
    if (timer<60){
	bg[timer].copyBG(); 
	}
	else
	{
	  bg[60].copyBG();
	  }  
	}
	
	
class BG
{ 
 int sx,sy,swidth,sheight,dx,dy,dwidth,dheight;
  
 BG()
 {
   sx=0; sy=0; swidth=width; sheight=height; dx=0; dy=0; dwidth=width; dheight=height;
   }
   
   void copyBG()
   {
     copy(sx,sy,swidth,sheight,dx,dy,dwidth,dheight);
     }
  }



and that:


Code:

int ex;
BG bg[] = new BG [frameCount]; 

void setup()
{
  size(400,400);
  background(255);
  bg = new BG[frameCount];
  
   framerate(30);  
  }
  
void draw()
  {
  
  drawBG();
  circle();
  }
  
     void circle()
    {    
	noStroke();
	fill(0,255,0);
	ellipse(ex,width/2,10,10);  
	ex++;
	}
	
    void drawBG()
    {
	//bg = expand(bg,frameCount);
	if (frameCount<60)
	{
	bg[frameCount] = expand(bg[frameCount-1],frameCount);
//error: "type of right sub-expression java.lang.Object is //not assignable to the variable of type BG()"
//expand only with booleans[], bytes[], chars[], ints[], //floats[], or Strings[]

	bg[frameCount].copyBG();
     // bg[frameCount-1].copyBG();
     }
     else 
     { 
     bg[60].copyBG();
     }
	}
	     
class BG
{
  
  /*float [] sx=new float[0];
  float [] sy=new float[0];
  float [] swidth=new float[width];
  float [] sheight=new float[height];
  float [] dx=new float[0];
  float [] dy=new float[0];
  float [] dwidth=new float[width];
  float [] dheight=new float[height];*/
  
 int sx,sy,swidth,sheight,dx,dy,dwidth,dheight;
  
 BG()
 {
   sx=0; sy=0; swidth=width; sheight=height; dx=0; dy=0; dwidth=width; dheight=height;
   }
   
   void copyBG()
   {
     copy(sx,sy,swidth,sheight,dx,dy,dwidth,dheight);
     }
  }



Intention: using the current status of the display window as background picture to keep the trace of a moving object (although "background" is within "draw()") until a certain point of time, then repeating just one frame (No. 60), so moving objects don´t leave trace anymore. I hope it is understandable, what i mean.

Problem: The frames are collected in an array that needs to be expanded with every loop.Till now i didn´t manage this (see code). Perhaps someone knows, why?
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« Last Edit: Sep 24th, 2006, 5:26pm by brin »  
 
Daniel Shiffman
Re: expand array
Reply #1 - Sep 24th, 2006, 10:24pm  
the expand() method only works with arrays of primitive values -- integers, floats, etc. Since your array is of BG *objects*, it cannot be resized at any point with expand() during the course of the program.  You could either create a very large array (and just you the part that you need at any given time) or else you could investigate using an ArrayList.  An ArrayList is a resizable ordered collection of objects.

http://java.sun.com/j2se/1.4.2/docs/api/java/util/ArrayList.html

Using an ArrayList like an array looks like this:

Code:

// Declaring the arraylist
ArrayList plist = new ArrayList() ;

// Adding elements
for (int i = 0; i < 10; i++) {
  plist.add(new Particle()) ;
}

// Accessing elements
for (int i = 0; i < plist.size() ; i++) {
  Particle p = (Particle) plist.get(i) ;
  p.run();
}


Full examples:
http://www.shiffman.net/teaching/the-nature-of-code/particles/
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fry
Re: expand array
Reply #2 - Sep 25th, 2006, 5:09am  
ArrayList is useful when you need a list of items.. however, with more recent releases, expand() works on all types of Objects, you just have to cast the result of the expand, i.e.

BG[] items = (BG[]) expand(originalArray);
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Daniel Shiffman
Re: expand array
Reply #3 - Sep 25th, 2006, 5:13am  
Oops, I didn't realize that re: expand(). . . good to know!
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brin
Re: expand array
Reply #4 - Sep 26th, 2006, 12:29am  
Thanks a lot for the replies!
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brin
Re: expand array
Reply #5 - Sep 28th, 2006, 10:25pm  
I keep getting two error messages which i don´t understand:

Code:

int ex;
BG bg[] = new BG [1];

void setup()
{
  size(400,400);
  background(255);
  bg = new BG[1];
  framerate(30); 
  }
  
void draw()
  {  int timer=frameCount;
     BG[] items = (BG[]) expand(bg, timer);
     println(items.length);//timer = items = 1
      
      if (timer<60)
      {
      items.copyBG();
//No accessible method with signature "copyBG()" was found in type "Temporary...BG[]"

      //items[timer].copyBG();
//java.lang.ArrayIndexOutOfBoundsException: 1
     }
     else if  (timer>=60)
     { 
     items[60].copyBG();
     }
    //println(bg.length);
  }


class BG
{
  
 int sx,sy,swidth,sheight,dx,dy,dwidth,dheight;
  
 BG()
 {
   sx=0; sy=0; swidth=width; sheight=height; dx=0; dy=0; dwidth=width; dheight=height;
   }
   
   void copyBG()
   {
     copy(sx,sy,swidth,sheight,dx,dy,dwidth,dheight);
     }
  }



java.lang.ArrayIndexOutOfBoundsException: 1
--> when this line is called: timer = frameCount = 1 (because first loop). That´s correct in my opinion. Why this OutOfBounds-error?

No accessible method with signature "copyBG()" was found in type "Temporary...BG[]"
--> What´s wrong with the class declaration?
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Daniel Shiffman
Re: expand array
Reply #6 - Sep 29th, 2006, 12:24am  
//No accessible method with signature "copyBG()" was found in type "Temporary...BG[]"

This error is due to the fact that "items" (i.e. the array as a whole) is not a BG object.  It is a list of BG objects.  You must call the copyBG() on an individual element of the array, indicated by an index value, i.e.:

Code:

items[0].copyBG();  // or some variable instead of 0


The other error occurs when you try to access index #60 of the array.  You'll notice at that time, the array is of length 60.  Since array indices start at 0, an array with length 60 has index values 0 through 59. There is no element #60!  In this case, you'd want to access element 59.  Or better yet, you can dynamically access the last element by asking for the length minus one.

Code:

items[items.length-1].copyBG();


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brin
Re: expand array
Reply #7 - Sep 29th, 2006, 9:56pm  
ok, i understood that now:
Code:

items[items.length-1].copyBG();


i found out, that there is some fault in the class definition (copyBG() doesn´t work)and thought of a way without using a class. The following does at least half of what i want to (i.e. leave a trace first and move further without trace) - but the trace is lost!

Code:

int ex=0;
PImage b;

void setup() 
{ 
  size(400,400); 
  background(255);
  framerate(30); 
  b = new PImage(width,height);
  b = get();
  smooth();
  } 
   
void draw() 
  { 
     int timer=frameCount; 
     
     if (timer<60)
      {  
     copy(0,0,width,height,0,0,width,height); 
      } 

     else if  (timer>=60) 
     { 
     image (b,0,0);
     } 

   ex++;
   ellipse(ex,height/2,10,10);
  }


isn´t there any possibility to save the screen at a certain point of time and use this picture as background?

instead of
Code:

 b = get();


i´d like to do someting like this:
Code:

 b = copy(0,0,width,height,0,0,width,height);


which causes the error "An expression of type "void" is not valid in this context where a value is expected."


i also rewrote the class BG:
Code:

class BG 
{ 
   
 int sx,sy,swidth,sheight,dx,dy,dwidth,dheight; 
   
 BG(int ssx,int ssy,int sswidth,int ssheight,int ddx,int ddy,int ddwidth,int ddheight) 
 { 
   sx=ssx; sy=ssy; swidth=sswidth; sheight=ssheight; dx=ddx; dy=ddy; dwidth=ddwidth; dheight=ddheight; 
   } 
    
   void copyBG() 
   { 
     copy(sx,sy,swidth,sheight,dx,dy,dwidth,dheight); 
     }
  }


, so i should write something (global) like

Code:

BG bg[] = new BG (0,0,width,height,0,0,width,height);


to pass values to the variables inside the class.
BUT:

Semantic Error: The type of the right sub-expression, "Temporary_...$BG", is not assignable to the variable, of type "Temporary_...$BG[]".

Sorry for all these beginner questions!
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« Last Edit: Sep 29th, 2006, 11:58pm by brin »  
 
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