Display and divide the image

[kiransu123]

hi
i m kiran suryawanshi
i m final year student i m working on the project called as "tiled image viewer"
In this i suppose to display image on tiled display i.e four monitors clustered together
for that i hv to display and divide the image
so i write the following code but i had problem saying that "Segmentation fault"

i m represting problem area btn <problem></problem> tag
plz help me

#include "qgl.h"
#include "qapplication.h"
#include "qimage.h"
#include "iostream.h"
#include "GL/gl.h"
class Radha : public QGLWidget
{
	public:
		Radha(const QString &filename,QWidget *parent=0);
		void paintGL();
		void resizeGL(int w,int h);
		void divide();
	protected:
		QImage data,gldata;
};
 
Radha::Radha(const QString &filename,QWidget *parent):QGLWidget(parent){
	data.load(filename);
	gldata=QGLWidget::convertToGLFormat(data);
	resize(data.size());
 
}
 
void Radha::paintGL(){
	int k,i,j,count=0,flag=1;	
<PROBLEM>	
	uchar *temp;
	uchar *img;
	temp=gldata.bits();
 
	for(j=0;j<data.width()*data.height();j++){  //for reading the half image in img array
			if(count==data.width()/2){
			flag==1-flag;	
			count=0;
		}
		if(flag==1)
			img[j++]=temp[i]; 
		count++;
	}
 
	glDrawPixels(data.width(),data.height(),GL_RGBA,GL_UNSIGNED_BYTE,img);
 
}
 
 
void Radha::resizeGL(int w,int h){
	glViewport(0,0,w,h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0,w,0,h,-1,1);
	glMatrixMode(GL_MODELVIEW);
 
}
 
int main(int argc,char** argv){
	QApplication app(argc,argv);
	Radha pw(argv[1]);
	pw.showFullScreen();
	return app.exec();
}

#include "qgl.h"
#include "qapplication.h"
#include "qimage.h"
#include "iostream.h"
#include "GL/gl.h"
class Radha : public QGLWidget
{
	public:
		Radha(const QString &filename,QWidget *parent=0);
		void paintGL();
		void resizeGL(int w,int h);
		void divide();
	protected:
		QImage data,gldata;
};

Radha::Radha(const QString &filename,QWidget *parent):QGLWidget(parent){
	data.load(filename);
	gldata=QGLWidget::convertToGLFormat(data);
	resize(data.size());
	
}

void Radha::paintGL(){
	int k,i,j,count=0,flag=1;	
<PROBLEM>	
	uchar *temp;
	uchar *img;
	temp=gldata.bits();
		
	for(j=0;j<data.width()*data.height();j++){  //for reading the half image in img array
			if(count==data.width()/2){
			flag==1-flag;	
			count=0;
		}
		if(flag==1)
			img[j++]=temp[i]; 
		count++;
	}

	glDrawPixels(data.width(),data.height(),GL_RGBA,GL_UNSIGNED_BYTE,img);

}


void Radha::resizeGL(int w,int h){
	glViewport(0,0,w,h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0,w,0,h,-1,1);
	glMatrixMode(GL_MODELVIEW);
	
}

int main(int argc,char** argv){
	QApplication app(argc,argv);
	Radha pw(argv[1]);
	pw.showFullScreen();
	return app.exec();
}

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[jacek]

Where do you initialize i and img and what do you need k for?

[kiransu123]

k is useless
is there any need to initialize the img
it is not showing some error but after executing it is showing "Segmentation fault"

[jacek]

k is useless

So there is no point in declaring it.

is there any need to initialize the img

Of course there is. It points at some random place in memory, so you can't use it until you initialize it.

[kiransu123]

can u tell me how to divide the image in 4 parts

[jacek]

can u tell me how to divide the image in 4 parts

Use QImage::copy().

[kiransu123]

Use QImage::copy().

how QImage::copy() is used bcz for this how can u specify the image
its syntax is copy(x,y,w,h)const
wht this const signifies

[Brandybuck]

QImage QImage::copy ( const QRect & rectangle = QRect() ) const
Returns a sub-area of the image as a new image.

If you want to subdivide an image into four sub-images, then you can use QImage::copy(). It is simply a matter of rectangles! Take one large rectangle and divide it into four small rectangles. You do not even need to know arithmetic, because QRect::center() will give you the QPoint in the center of the rectangle.

p.s. The "const" in the method signature means that it is a constant function, which does not modify the object. The use of QImage::copy() will not modify the QImage it is called with.

[kiransu123]

If you want to subdivide an image into four sub-images, then you can use QImage::copy(). It is simply a matter of rectangles! Take one large rectangle and divide it into four small rectangles. You do not even need to know arithmetic, because QRect::center() will give you the QPoint in the center of the rectangle.

p.s. The "const" in the method signature means that it is a constant function, which does not modify the object. The use of QImage::copy() will not modify the QImage it is called with.

then how can i display using glDrowPixels() bcz the last argument require for it is pointer to image so wht should i pass to it
thanks for solution

[fullmetalcoder]

then how can i display using glDrowPixels() bcz the last argument require for it is pointer to image so wht should i pass to it
thanks for solution

I think you're handling this in a wrong way. Qt has built-in facilities for rendering images (with or without OpenGL) and manipulating them. Instead of mixing Qt classes and OpenGl calls you should choose a single approach : either plain Qt (using QtOpenGl module) or plain C/OpenGl with possibly some helper libs to handle images loading...

[kiransu123]

I think you're handling this in a wrong way. Qt has built-in facilities for rendering images (with or without OpenGL) and manipulating them. Instead of mixing Qt classes and OpenGl calls you should choose a single approach : either plain Qt (using QtOpenGl module) or plain C/OpenGl with possibly some helper libs to handle images loading...

can u tell me how should i proceed further to divide the image in 4 parts using QT
wht r built in facililies for this problem

[kiransu123]

Hi I m kiran
i want to display an image then divide it and again display the part of the image.
Is is possibe in QImage to read the image in the array so i can perform some manipulation on the image

i m reading the image as follows the problem is that how can i read the image the array
I indicate the problem area in <problem></problem> tag in paintGL() function.

#include "qgl.h"
#include "qapplication.h"
#include "qimage.h"
class PaintWidget : public QGLWidget{
	public:
		PaintWidget(const QString &filename,QWidget *parent=0);
		void paintGL();
		void resizeGL(int w,int h);
	protected:
		QImage data,gldata;
};
 
PaintWidget::PaintWidget(const QString &filename,QWidget *parent):QGLWidget(parent){
	data.load(filename);
	gldata=QGLWidget::convertToGLFormat(data);
	resize(data.size());
}
 
 
void PaintWidget::paintGL(){
       int k,i,j,count_h=0,count_v=0,flag=1;
       uchar *temp;
       uchar *img;
       temp=gldata.bits();
//<problem>
       for(i=0;i<gldata.width()*gldata.height();i++){ 
	        if(count_h==gldata.width()/2){      //checking for first half of image
                 flag=1-flag;                        // flag =1 : 1st half  flag=0 : second half
                 count_h=0;                           // for counting next half counter make zero
             }
             if(flag==1)
                 img[++j]=temp[i];  //img[j++]will read only half of the image therefore j++
             count_h++;
        }
 
 
       glDrawPixels(data.width(),data.height(),GL_RGBA,GL_UNSIGNED_BYTE,img);
 
 //</problem>   //glDrawPixels(data.width(),data.height(),GL_RGBA,GL_UNSIGNED_BYTE,gldata.bits());
}
 
void PaintWidget::resizeGL(int w, int h){
	glViewport(0,0,w,h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0,w,0,h,-1,1);
	glMatrixMode(GL_MODELVIEW);
}
 
int main(int argc, char** argv){
	QApplication app(argc,argv);
	PaintWidget pw(argv[1]);
	pw.show();
	return app.exec();
 
}

#include "qgl.h"
#include "qapplication.h"
#include "qimage.h"
class PaintWidget : public QGLWidget{
	public:
		PaintWidget(const QString &filename,QWidget *parent=0);
		void paintGL();
		void resizeGL(int w,int h);
	protected:
		QImage data,gldata;
};

PaintWidget::PaintWidget(const QString &filename,QWidget *parent):QGLWidget(parent){
	data.load(filename);
	gldata=QGLWidget::convertToGLFormat(data);
	resize(data.size());
}


void PaintWidget::paintGL(){
       int k,i,j,count_h=0,count_v=0,flag=1;
       uchar *temp;
       uchar *img;
       temp=gldata.bits();
//<problem>
       for(i=0;i<gldata.width()*gldata.height();i++){ 
	        if(count_h==gldata.width()/2){      //checking for first half of image
                 flag=1-flag;                        // flag =1 : 1st half  flag=0 : second half
                 count_h=0;                           // for counting next half counter make zero
             }
             if(flag==1)
                 img[++j]=temp[i];  //img[j++]will read only half of the image therefore j++
             count_h++;
        }


       glDrawPixels(data.width(),data.height(),GL_RGBA,GL_UNSIGNED_BYTE,img);

 //</problem>   //glDrawPixels(data.width(),data.height(),GL_RGBA,GL_UNSIGNED_BYTE,gldata.bits());
}

void PaintWidget::resizeGL(int w, int h){
	glViewport(0,0,w,h);
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(0,w,0,h,-1,1);
	glMatrixMode(GL_MODELVIEW);
}

int main(int argc, char** argv){
	QApplication app(argc,argv);
	PaintWidget pw(argv[1]);
	pw.show();
	return app.exec();

}

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