Accessing protected PGraphics vars by subclassing in anonymous package

General Discussion Other

codekiln

Accessing protected PGraphics vars by subclassing in anonymous package

in General Discussion • Other • 2 years ago

I'm writing a class to add HTML textarea functionality to Processing's built-in text(String, int, int, int, int) function. I'd like to subclass PGraphics so I can gain access to the protected fields int[] textBreakStart and int[] textBreakStop. I found this forum post from 2010 where antiplastik explains the proper way to subclass PGraphics is to call:

Classname varname = (Classname) createGraphics(width, height, "packagename.Classname")

What parameters would I use to call this with a class declared in the anonymous package, inside a processing sketch? This doesn't work:

class MyPG extends PGraphics2D {
}
void setup() {
MyPG mypg = (MyPG) createGraphics( width, height, "MyPG" );
}
// result:
//
// Exception in thread "Animation Thread" java.lang.RuntimeException: You need to use "Import Library" to add MyPG to your sketch.
// at processing.core.PApplet.makeGraphics(Unknown Source)
// at processing.core.PApplet.createGraphics(Unknown Source)
// at subclass_pgraphics.setup(subclass_pgraphics.java:21)
// at processing.core.PApplet.handleDraw(Unknown Source)
// at processing.core.PApplet.run(Unknown Source)
// at java.lang.Thread.run(Thread.java:662)

Replies(3)

codekiln

Re: Accessing protected PGraphics vars by subclassing in anonymous package

2 years ago

Since I haven't been able to figure out the answer to my question, I've started writing a library so I can use a package. It's been over a year since I've written a Processing library, and I'm getting the "needs to be updated for the current release of Processing" error. That error is rather vague - what do I need to do to update for the current release of Processing?

Here's my library:

package us.norepeter;
import java.awt.event.KeyEvent;
import java.awt.event.MouseEvent;
import processing.core.PApplet;
import processing.core.PGraphics2D;
public class PTextarea {
Pg2 pg2;
String s = "Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";
public PTextarea(PApplet p) {
pg2 = (Pg2) p.createGraphics(800, 600, "us.norepeter.PTextarea");
pg2.text(s, 50, 50, 200, 200);
int[] start = pg2.getTextBreakStart();
p.println("start is " + (start == null ? "here" : "null"));
p.noLoop();
}
class Pg2 extends PGraphics2D {
int[] getTextBreakStart() {
return super.textBreakStart;
}
int[] textBreakStop() {
return super.textBreakStop;
}
}
public void pre() {
}
public void draw() {
}
public void post() {
}
public void mouseEvent(MouseEvent e) {
}
public void keyEvent(KeyEvent e) {
}
public void size(int width, int height) {
}
public void stop() {
}
public void dispose() {
}
public void init() {
}
}

Here's the test patch:

import us.norepeter.*;
PTextarea pt;
void setup() {
size(800, 600);
pt = new PTextarea(this);
}

Here's the stackdump:

java.lang.NoSuchMethodException: us.norepeter.PTextarea.<init>()
at java.lang.Class.getConstructor0(Class.java:2706)
at java.lang.Class.getConstructor(Class.java:1657)
at processing.core.PApplet.makeGraphics(Unknown Source)
at processing.core.PApplet.createGraphics(Unknown Source)
at us.norepeter.PTextarea.<init>(PTextarea.java:21)
at basic.setup(basic.java:28)
at processing.core.PApplet.handleDraw(Unknown Source)
at processing.core.PApplet.run(Unknown Source)
at java.lang.Thread.run(Thread.java:662)
Exception in thread "Animation Thread" java.lang.RuntimeException: us.norepeter.PTextarea needs to be updated for the current release of Processing.
at processing.core.PApplet.makeGraphics(Unknown Source)
at processing.core.PApplet.createGraphics(Unknown Source)
at us.norepeter.PTextarea.<init>(PTextarea.java:21)
at basic.setup(basic.java:28)
at processing.core.PApplet.handleDraw(Unknown Source)
at processing.core.PApplet.run(Unknown Source)
at java.lang.Thread.run(Thread.java:662)

PhiLho

Re: Accessing protected PGraphics vars by subclassing in anonymous package

2 years ago

Apparently, it wants a constructor without parameters.

codekiln

Re: Re: Accessing protected PGraphics vars by subclassing in anonymous package

2 years ago

Hi phi.lho,

Thanks for your response. After I added an explicitly public no-op constructor for each class, I stopped getting the vague " needs to be updated for the current release of Processing" error message that sent me ineffectually digging through line 1369 of PApplet.java, inside makeGraphics() last night.

I'll have to update the LibraryBasics wiki page with the new info.

Just for the googlers, this is what was necessary to get at the protected vars in PGraphics:

Make a library that doesn't use the default package
Make a class that will be your library gateway that has both a constructor that takes a PApplet and a public zero-parameter constructor (thanks phi.lho)
Make another public class that's not an inner class that extends not PGraphics but one of the PGraphics subclasses. Give this class a public zero-parameter constructor.
Give the PGraphics subclass getter methods to etract the protected variables
Instantiate the PGraphics by supplying a fully qualified package name class name as a string to the third parameter of PApplet.createGraphics and casting it to your subclass
When you are accessing the vars, it's probably necessary to call beginDraw() and endDraw() on your PGraphics subclass instance before accessing the vars

Simple demonstration: --------------------------

PTextareaLibrary.java:

package textarea.library;
import processing.core.*;
public class PTextareaLibrary {
TextGraphics pg2;
String s = "Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.";
PApplet p;
public PTextareaLibrary(){}
public PTextareaLibrary(PApplet p) {
this.p = p;
}
public int[] getTextBreakStarts() {
pg2 = (TextGraphics) p.createGraphics(p.width, p.height, "textarea.library.TextGraphics");
pg2.beginDraw();
pg2.text(s,50, 50, 200, 200);
pg2.endDraw();
return pg2.getTextBreakStart();
}
}

TextGraphics.java:

package textarea.library;
import processing.core.*;
public class TextGraphics extends PGraphics2D {
public TextGraphics() { /* do stuff here */ }
int[] getTextBreakStart() {
return super.textBreakStart;
}
int[] textBreakStop() {
return super.textBreakStop;
}
}

example.pde:

import textarea.library.*;
PTextareaLibrary pt;
void setup() {
size(800, 600);
pt = new PTextareaLibrary(this);
int[] start = pt.getTextBreakStarts();
println( start );
}

If you find yourself getting RSI you might consider authoring a library PGraphicsGenie that uses reflection to enable unfettered access from inside the processing environment.

Top Reply