Class question

beginners
#1

Hi everyone

I am new in OF, I follow the tutorials in OF wiki “Ooops! = Object Oriented Programming + Classes”, those are
pretty clear to understand how create classes, but I have two questions.

  1. How can I create a class (draw the ball) from events, for example by mouse pressed or touch event on iOS ?
  2. How cam I delete the class from event, delete the ball ?

I have experience in Action Script and Lingo, and I am so confused, becouse I dont understand how
remove the class that I create.

Please help!

Thanks

#2

Hi everyone

I am new in OF, I follow the tutorials in OF wiki “Ooops! = Object Oriented Programming + Classes”, those are
pretty clear to understand how create classes, but I have two questions.

  1. How can I create a class (draw the ball) from events, for example by mouse pressed or touch event on iOS ?
  2. How cam I delete the class from event, delete the ball ?

I have experience in Action Script and Lingo, and I am so confused, becouse I dont understand how
remove the class that I create.

Please help!

Thanks

#3

you have to do a pointer to an object like this

  
ofBall *myBall;

and then add to the mousePressed method something like

  
myBall = new Ball(...);

and remove the ball on lets say keyPressed with something like

  
delete myBall;

to create more than one Ball you have to create a vector or array of balls.
look at the and of the tutorial:
http://wiki.openframeworks.cc/index.php?title=Ooops%21-%3D-Object-Oriented-Programming-%2B-Classes#make-objects-from-your-own-Classes—part-3

#4

Hi benben

Thanks for your answer!

I try this, but I dont understand how to use the draw() method and update() method, I am drawing the ball
in the draw() method of Ball class,

void Ball::draw()
{
ofSetColor(200, 200, 200);
ofCircle(x, y, dim);
}

then if I dont call the draw method in the draw() method of the testAPP class, the program draw noting, but if I call the draw() method of the Ball class the app crash.

void testApp::draw(){

myBall->draw();

}

I understand how pointer a class and how create a new instance of this class, but relation of draw and update method inter classes, is hard to me

#5

it would be better if you post the complete code of testApp.h and testApp.cpp, so we can see what you did wrong.

here is an example with a vector of balls. on left click a ball is created, on right-click the last created ball is removed. (because of the pop_back())

testApp.h

  
#ifndef _TEST_APP  
#define _TEST_APP  
  
#include "ofMain.h"  
#include "ofBall.h"  
  
class testApp : public ofSimpleApp{  
  
   public:  
  
      void setup();  
      void update();  
      void draw();  
	  void mouseReleased(int x, int y, int button);  
  
  
   private:  
  
	 	vector<ofBall*> myBall;  
};  
  
#endif

testApp.cpp

  
#include "testApp.h"  
  
//--------------------------------------------------------------  
void testApp::setup(){  
  
	ofBackground(0,0,0);  
	ofSetFrameRate(30);  
	ofSetWindowTitle("balls - class example_4");  
  
	ofEnableSmoothing();  
	ofNoFill();  
}  
  
//--------------------------------------------------------------  
void testApp::update(){  
  
		for (int i = 0; i < myBall.size(); i++){  
			myBall[i]->update();  
		}  
}  
  
//--------------------------------------------------------------  
void testApp::draw(){  
  
		for (int i = 0; i < myBall.size(); i++){  
			myBall[i]->draw();  
		}  
}  
  
void testApp::mouseReleased(int x, int y, int button)  
{  
    if(button == 0)  
    {  
        int dim = 10+(ofRandom(0,10)*10);  
        myBall.push_back(new ofBall(ofRandom(0, ofGetWidth()),ofRandom(0, ofGetHeight()),dim));  
    }  
    else if (button == 2)  
    {  
        if(myBall.size() > 0)  
        {  
            myBall.pop_back();  
        }  
    }  
}
#6

first some lingo: a class is a generic prototype, when you actually use it to create a ball or anything else you are creating an object.

first answer: if you only need to create a single object from your class, you’ll probably want to declare it globally and use your mouse pressed event to actually render it:

  
  
//in testApp.h  
Ball myBall;  
...  
//in testApp.cpp  
void testApp::draw(){  
...  
   myBall.draw(); //where Ball.draw() i.e. draws the ball at Ball.x, Ball.y  
...  
}  
...  
void testApp::mousePressed(int x, int y, int button){  
...  
   myBall.x = x;  
   myBall.y = y;  
   //this way when you press mouse myBall will be drawn at mouse coords  
...  
}

if you need to handle more Ball objects you’ll probably want to learn about arrays and vectors.

second answer: again, if you need to work with a single Ball you could simply move it out of the screen, if you’re handling more you’ll want to learn about vectors and push_back() and pop_back() functions.

#7

One quick point:

  
  
        if(myBall.size() > 0)    
        {    
            ofBall* toBeDeleted = myBall.back(); // get the last ptr  
            delete toBeDeleted; // free its memory  
            myBall.pop_back();    
        }
#8

I merged the two identical threads. nogram, please refrain from doubleposting in the future.

#9

benben and naus3a post really good examples.

Check out the Basic Particle System section in the wiki page, they explain how to create particles from a Particle class.

http://wiki.openframeworks.cc/index.php?title=Basic-particle-system

Then you can move the create_particles() to touchDown() or mousePressed(), to delete the particles check they use a C++ list container, check out the docs http://www.cplusplus.com/reference/stl/list/ you can use erase, and pop methods to delete the particles

Hope that helps!

#10

Hi guys!!

Thanks a lot for your help!

I did not know about vector and list functions, finally I understood.

I am wondering, is posible to create a whole scene with this method, or are there other way for this?
I mean, create a loading scene, instruction scene and game scene, and be able to navegate through them.