QGLWidget renderText() problem in openGL.

[pastispast]

Hi Friends,

I am getting problem using the render text function in openGL.

Actually I want to use openGL with QGraphicsView in my application. So I am using class QGraphicsItem to achieve this. I have used renderPixmap() function. But when I execute my function I got the text but soon there is a crash.

I have search across the forum and found that

"renderText is 8-bit and can only use "OpenGL compatible fonts".

So I have used the following code to do this:

QFont myFont("Verdana", 24);
myFont.setStyleStrategy(QFont.OpenGLCompatible);
renderText(20,20, 0,"test", myFont);

What can be cause of the problem...

I have also attached the code [Older one already posted in previous thread].

My QT version is "Qt by Nokia v4.7.0 (VS2008)"

[john_god]

What happens if you use

renderText(20,20, 0,"test");

renderText(20,20, 0,"test");

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[pastispast]

What happens if you use

renderText(20,20, 0,"test");

renderText(20,20, 0,"test");

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I have tried this["renderText(20,20, 0,"test")"] also and even renderText(20,20,"test"), but no result...again application crashed....

Is anything I am missing????

[tbscope]

Can you post the crash report?

[pastispast]

Can you post the crash report?

Hi tbscope,

Thanks for the reply...I have attached the crash report...[Image + Call Stack + Error Report]

ScreenShot.jpg7339_appcompat.txtCall Stack.txt

[tbscope]

I can't see a problem in the stack trace.

Can you post the full code please (make it minimal and compilable)?

[pastispast]

I can't see a problem in the stack trace.

Can you post the full code please (make it minimal and compilable)?

Once again thanks for the reply...

I have attached the code along with this mail, and also I have added the snippet of code for your reference...

//main.cpp
#include "openglsceneexample.h"
 
#include <QtGui>
#include <QApplication>
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    OpenGLSceneExample w;
    w.show();
    return a.exec();
}

//main.cpp
#include "openglsceneexample.h"

#include <QtGui>
#include <QApplication>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    OpenGLSceneExample w;
    w.show();
    return a.exec();
}

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//openglsceneexample.cpp
 
#include "openglsceneexample.h"
 
#include <QtGui>
#include <QGLWidget>
 
////////////////////////////////////////////////////////////////////////////////////////////////
//////////////////// OPEN GL WIDGET
 
CEasyGLWidget::CEasyGLWidget(QWidget *parent)
: QGLWidget(QGLFormat(QGL::SampleBuffers/*|QGL::AlphaChannel|QGL::HasOverlay|QGL::Rgba*/),parent) 
 
{
	m_pOGLObject = 0;
}
 
CEasyGLWidget::~CEasyGLWidget()
{
 
}
 
 
/*! \brief Draws a single circular or elliptical arc.
 * 
 *\param  cx 			Upper Left corner of the in x coordinates
 *\param  cy 			Upper Left corner of the in y coordinates
 *\param  r				Radius of the arc.
 *\param  start_angle 	Start position in angles (radian)
 *\param  arc_angle 	Angle of the Arc in radian
 *\param  num_segments  Point count, which represent the arc
 */
void CEasyGLWidget::DrawArc(GLdouble cx, GLdouble cy, GLdouble r, GLdouble start_angle, GLdouble arc_angle, int num_segments)
{
	//Theta is calculated from the arc angle, the -1 bit comes from the fact that the arc is open 
	GLdouble theta = arc_angle / GLdouble(num_segments -1);
	GLdouble tangetial_factor = tanf(theta);
 
	GLdouble radial_factor = cosf(theta);
 
	//start at the start angle
	GLdouble  x = r * cosf(start_angle);
	GLdouble  y =  r * sinf(start_angle);
 
	glBegin(GL_LINE_STRIP);
 
	for(int i = 0; i < num_segments; i++)
	{
		glVertex2f(x + cx + r, y + cy +r); //, 0.5);
 
		GLdouble tx = -y;
		GLdouble ty = x;
 
		x += tx * tangetial_factor;
		y += ty * tangetial_factor;
 
		x *= radial_factor;
		y *= radial_factor;
	}
 
	glEnd();
}
 
 
/*! \brief Draws a single line.
 * 
 * \param[in] cStartPoint Start Point of the line to be drawn.
 * \param[in] cDestPoint  Destination Point of the line to be drawn.
 */
void CEasyGLWidget::DrawLine(QPointF cStartPoint, QPointF cDestPoint)
{
	glBegin(GL_LINE_STRIP);
 
	glVertex2f(cStartPoint.rx(), cStartPoint.ry()); 
	glVertex2f(cDestPoint.rx(), cDestPoint.ry());
 
	glEnd();
}
 
void CEasyGLWidget::initializeGL()
{
	qglClearColor( QColor(90,125,164,255)); //set background color
 
	qglColor(QColor(255,0,0,255));
 
	//create a display list containing information about the object we want to display
    m_pOGLObject = glGenLists(1);
 
    glNewList(m_pOGLObject, GL_COMPILE);
    DrawArc(0.0, 0.0, 30.0, 0.0, 2*PI, 60);
 
    DrawLine(QPointF(0.0,0.0), QPointF(200.0,200.0));
    glEndList();
 
	//activate alpha values for transparent colors of the bitmaps
	glEnable(GL_ALPHA_TEST);   
	glAlphaFunc(GL_GREATER,0.1);
 
	//set up the rendering process to use a particular shading model and rendering flags:
	glShadeModel(GL_FLAT);
}
 
void CEasyGLWidget::resizeGL(int iWidth, int iHeight)
{
	 // Set size of the view port (display size)
	 glViewport(0,0,(int)MIN(iWidth,iHeight), (int)MIN(iWidth,iHeight)); // always use width=height
 
	 glMatrixMode(GL_PROJECTION); //select protection matrix
	 glLoadIdentity();  //reset matrix position to start
 
	 // Open gl always draws on the same matrix (width x height = fix defined hud size) 
	 // the size is defined by the Ortho Matrix. 
	 // This matrix is scaled to the destination size.
	 glOrtho(0, 400,400, 0, -1,1); 
 
	 glMatrixMode(GL_MODELVIEW);  //select model view (result) matrix
}
 
void CEasyGLWidget::paintGL()
{
 
         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear background using background color
         glLoadIdentity();              //reset matrix position to start
         glTranslatef(0.0, 0.0, 0.0) ; // move object to dest position
         glCallList(m_pOGLObject);     // call the display list containing the rendering commands for the object
 
         QFont myFont("Verdana", 24);
         myFont.setStyleStrategy(QFont.OpenGLCompatible);
         renderText(20,20, 0,"test", myFont);
 
}
 
 
/////////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////// ITEM
 
CEasyGraphicsItem::CEasyGraphicsItem(QWidget *parent)
{
	m_OGLItem = new CEasyGLWidget();
	m_OGLItem->resize(200,200);
        m_Pixmap = m_OGLItem->renderPixmap(600,600);
}
CEasyGraphicsItem::~CEasyGraphicsItem()
{
 
}
 
void CEasyGraphicsItem::paint ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget)
{
	 QRectF rect(0.0,0.0,200.0,200.0);
 
	 //Works fine !!
	 //painter->drawArc(rect,0,16*360);
 
	 // Open gl element is not displayed!!!
	//m_pPixmap = QPixmap::grabWidget(m_OGLItem,0,0,600,600); 
	m_Pixmap = m_OGLItem->renderPixmap(600,600);
	painter->drawPixmap(0,0,600,600,m_Pixmap); 
	//m_Image = m_OGLItem->grabFrameBuffer();
	//painter->drawImage(rect, m_Image); 
}
 
QRectF CEasyGraphicsItem::boundingRect() const
{	 
	return QRectF(0,0,600,600); //m_CurrWindowWidth,m_CurrWindowHeight);
}
////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////// MAIN Window
 
OpenGLSceneExample::OpenGLSceneExample(QWidget *parent)
    : QMainWindow(parent)
{
//	ui.setupUi(this);
 
	 m_pMainGraphicsScene = new QGraphicsScene();     
	 m_pMainGraphicsScene->setSceneRect(QRectF(0,0,630,630)); // Dummy window size
	 m_pMainGraphicsView = new QGraphicsView(m_pMainGraphicsScene);    
 
	 m_pMainGLWidget = new QGLWidget();
	 //m_pMainGraphicsView->setViewport(m_pMainGLWidget);
 
	 setCentralWidget(m_pMainGraphicsView); 
 
 
	 // Add open gl item  to view (not part of the scene!!) works fine!
	 /*m_OGLItem = new CEasyGLWidget(m_pMainGraphicsView); 
	 m_OGLItem->resize(400,400);
	 m_pMainGraphicsScene->addWidget(m_OGLItem);
	 */  
 
	 // add graphics item which contain a open gl element
	 m_pItem = new CEasyGraphicsItem();
	 m_pMainGraphicsScene->addItem(m_pItem);
 
 
}
 
OpenGLSceneExample::~OpenGLSceneExample()
{
 
}

//openglsceneexample.cpp

#include "openglsceneexample.h"

#include <QtGui>
#include <QGLWidget>

////////////////////////////////////////////////////////////////////////////////////////////////
//////////////////// OPEN GL WIDGET

CEasyGLWidget::CEasyGLWidget(QWidget *parent)
: QGLWidget(QGLFormat(QGL::SampleBuffers/*|QGL::AlphaChannel|QGL::HasOverlay|QGL::Rgba*/),parent) 

{
	m_pOGLObject = 0;
}

CEasyGLWidget::~CEasyGLWidget()
{
	
}
	

/*! \brief Draws a single circular or elliptical arc.
 * 
 *\param  cx 			Upper Left corner of the in x coordinates
 *\param  cy 			Upper Left corner of the in y coordinates
 *\param  r				Radius of the arc.
 *\param  start_angle 	Start position in angles (radian)
 *\param  arc_angle 	Angle of the Arc in radian
 *\param  num_segments  Point count, which represent the arc
 */
void CEasyGLWidget::DrawArc(GLdouble cx, GLdouble cy, GLdouble r, GLdouble start_angle, GLdouble arc_angle, int num_segments)
{
	//Theta is calculated from the arc angle, the -1 bit comes from the fact that the arc is open 
	GLdouble theta = arc_angle / GLdouble(num_segments -1);
	GLdouble tangetial_factor = tanf(theta);
	
	GLdouble radial_factor = cosf(theta);
	
	//start at the start angle
	GLdouble  x = r * cosf(start_angle);
	GLdouble  y =  r * sinf(start_angle);
	  
	glBegin(GL_LINE_STRIP);
	
	for(int i = 0; i < num_segments; i++)
	{
		glVertex2f(x + cx + r, y + cy +r); //, 0.5);
		
		GLdouble tx = -y;
		GLdouble ty = x;
		
		x += tx * tangetial_factor;
		y += ty * tangetial_factor;
		
		x *= radial_factor;
		y *= radial_factor;
	}
	
	glEnd();
}


/*! \brief Draws a single line.
 * 
 * \param[in] cStartPoint Start Point of the line to be drawn.
 * \param[in] cDestPoint  Destination Point of the line to be drawn.
 */
void CEasyGLWidget::DrawLine(QPointF cStartPoint, QPointF cDestPoint)
{
	glBegin(GL_LINE_STRIP);
	
	glVertex2f(cStartPoint.rx(), cStartPoint.ry()); 
	glVertex2f(cDestPoint.rx(), cDestPoint.ry());
	
	glEnd();
}

void CEasyGLWidget::initializeGL()
{
	qglClearColor( QColor(90,125,164,255)); //set background color
	
	qglColor(QColor(255,0,0,255));
	
	//create a display list containing information about the object we want to display
    m_pOGLObject = glGenLists(1);
    
    glNewList(m_pOGLObject, GL_COMPILE);
    DrawArc(0.0, 0.0, 30.0, 0.0, 2*PI, 60);
    
    DrawLine(QPointF(0.0,0.0), QPointF(200.0,200.0));
    glEndList();
    
	//activate alpha values for transparent colors of the bitmaps
	glEnable(GL_ALPHA_TEST);   
	glAlphaFunc(GL_GREATER,0.1);
	 
	//set up the rendering process to use a particular shading model and rendering flags:
	glShadeModel(GL_FLAT);
}
	
void CEasyGLWidget::resizeGL(int iWidth, int iHeight)
{
	 // Set size of the view port (display size)
	 glViewport(0,0,(int)MIN(iWidth,iHeight), (int)MIN(iWidth,iHeight)); // always use width=height
	
	 glMatrixMode(GL_PROJECTION); //select protection matrix
	 glLoadIdentity();  //reset matrix position to start
 
	 // Open gl always draws on the same matrix (width x height = fix defined hud size) 
	 // the size is defined by the Ortho Matrix. 
	 // This matrix is scaled to the destination size.
	 glOrtho(0, 400,400, 0, -1,1); 
	 
	 glMatrixMode(GL_MODELVIEW);  //select model view (result) matrix
}
	
void CEasyGLWidget::paintGL()
{

         glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); // Clear background using background color
         glLoadIdentity();              //reset matrix position to start
         glTranslatef(0.0, 0.0, 0.0) ; // move object to dest position
         glCallList(m_pOGLObject);     // call the display list containing the rendering commands for the object

         QFont myFont("Verdana", 24);
         myFont.setStyleStrategy(QFont.OpenGLCompatible);
         renderText(20,20, 0,"test", myFont);
	    
}


/////////////////////////////////////////////////////////////////////////////////////////////
/////////////////////////// ITEM

CEasyGraphicsItem::CEasyGraphicsItem(QWidget *parent)
{
	m_OGLItem = new CEasyGLWidget();
	m_OGLItem->resize(200,200);
        m_Pixmap = m_OGLItem->renderPixmap(600,600);
}
CEasyGraphicsItem::~CEasyGraphicsItem()
{
	
}
	
void CEasyGraphicsItem::paint ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget)
{
	 QRectF rect(0.0,0.0,200.0,200.0);
	 
	 //Works fine !!
	 //painter->drawArc(rect,0,16*360);
	 	 
	 // Open gl element is not displayed!!!
	//m_pPixmap = QPixmap::grabWidget(m_OGLItem,0,0,600,600); 
	m_Pixmap = m_OGLItem->renderPixmap(600,600);
	painter->drawPixmap(0,0,600,600,m_Pixmap); 
	//m_Image = m_OGLItem->grabFrameBuffer();
	//painter->drawImage(rect, m_Image); 
}

QRectF CEasyGraphicsItem::boundingRect() const
{	 
	return QRectF(0,0,600,600); //m_CurrWindowWidth,m_CurrWindowHeight);
}
////////////////////////////////////////////////////////////////////////////////////////////////////
////////////////// MAIN Window

OpenGLSceneExample::OpenGLSceneExample(QWidget *parent)
    : QMainWindow(parent)
{
//	ui.setupUi(this);
	
	 m_pMainGraphicsScene = new QGraphicsScene();     
	 m_pMainGraphicsScene->setSceneRect(QRectF(0,0,630,630)); // Dummy window size
	 m_pMainGraphicsView = new QGraphicsView(m_pMainGraphicsScene);    
	    
	 m_pMainGLWidget = new QGLWidget();
	 //m_pMainGraphicsView->setViewport(m_pMainGLWidget);

	 setCentralWidget(m_pMainGraphicsView); 
	 
	 
	 // Add open gl item  to view (not part of the scene!!) works fine!
	 /*m_OGLItem = new CEasyGLWidget(m_pMainGraphicsView); 
	 m_OGLItem->resize(400,400);
	 m_pMainGraphicsScene->addWidget(m_OGLItem);
	 */  
	 	 
	 // add graphics item which contain a open gl element
	 m_pItem = new CEasyGraphicsItem();
	 m_pMainGraphicsScene->addItem(m_pItem);

	 
}

OpenGLSceneExample::~OpenGLSceneExample()
{

}

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//openglsceneexample.h
 
#ifndef OPENGLSCENEEXAMPLE_H
#define OPENGLSCENEEXAMPLE_H
 
#include <QtGui>
#include <QGLWidget>
 
//#include "ui_openglsceneexample.h"
#define MIN(a,b)  ((a < b)? a : b)
#define PI            3.14159265358979323846 /*!< constant PI                         */
 
class CEasyGLWidget : public QGLWidget
{
	Q_OBJECT
 
public:
 
	CEasyGLWidget(QWidget *parent = 0);
	~CEasyGLWidget();
 
	 void initializeGL();
	 void resizeGL(int w, int h);
	 void paintGL();
 
	 void DrawArc(GLdouble cx, GLdouble cy, GLdouble r, GLdouble start_angle, GLdouble arc_angle, int num_segments);
	 void DrawLine(QPointF cStartPoint, QPointF cDestPoint);
private:
 
	GLuint             m_pOGLObject;  
 
};
 
 
class CEasyGraphicsItem : public QGraphicsItem
{
	//Q_OBJECT
 
public:
	CEasyGraphicsItem(QWidget *parent = 0);
	~CEasyGraphicsItem();
 
	virtual QRectF boundingRect() const;	
    virtual void paint ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget = 0 );
 
private:
	CEasyGLWidget *m_OGLItem;
	QPixmap m_Pixmap;
	QImage m_Image;
 
};
 
 
class OpenGLSceneExample : public QMainWindow
{
    Q_OBJECT
 
public:
    OpenGLSceneExample(QWidget *parent = 0);
    ~OpenGLSceneExample();
 
private:
    //Ui::OpenGLSceneExampleClass ui;
 
 
    QGraphicsScene  *m_pMainGraphicsScene;     
    QGraphicsView   *m_pMainGraphicsView;    
    QGLWidget       *m_pMainGLWidget;          
 
    CEasyGraphicsItem *m_pItem;
 
    CEasyGLWidget *m_OGLItem;
};
 
#endif // OPENGLSCENEEXAMPLE_H

//openglsceneexample.h

#ifndef OPENGLSCENEEXAMPLE_H
#define OPENGLSCENEEXAMPLE_H

#include <QtGui>
#include <QGLWidget>

//#include "ui_openglsceneexample.h"
#define MIN(a,b)  ((a < b)? a : b)
#define PI            3.14159265358979323846 /*!< constant PI                         */

class CEasyGLWidget : public QGLWidget
{
	Q_OBJECT
	
public:
	
	CEasyGLWidget(QWidget *parent = 0);
	~CEasyGLWidget();
	
	 void initializeGL();
	 void resizeGL(int w, int h);
	 void paintGL();
	 
	 void DrawArc(GLdouble cx, GLdouble cy, GLdouble r, GLdouble start_angle, GLdouble arc_angle, int num_segments);
	 void DrawLine(QPointF cStartPoint, QPointF cDestPoint);
private:
	
	GLuint             m_pOGLObject;  

};


class CEasyGraphicsItem : public QGraphicsItem
{
	//Q_OBJECT
	
public:
	CEasyGraphicsItem(QWidget *parent = 0);
	~CEasyGraphicsItem();
	
	virtual QRectF boundingRect() const;	
    virtual void paint ( QPainter * painter, const QStyleOptionGraphicsItem * option, QWidget * widget = 0 );

private:
	CEasyGLWidget *m_OGLItem;
	QPixmap m_Pixmap;
	QImage m_Image;
	
};


class OpenGLSceneExample : public QMainWindow
{
    Q_OBJECT

public:
    OpenGLSceneExample(QWidget *parent = 0);
    ~OpenGLSceneExample();

private:
    //Ui::OpenGLSceneExampleClass ui;
	
    
    QGraphicsScene  *m_pMainGraphicsScene;     
    QGraphicsView   *m_pMainGraphicsView;    
    QGLWidget       *m_pMainGLWidget;          
    
    CEasyGraphicsItem *m_pItem;
    
    CEasyGLWidget *m_OGLItem;
};

#endif // OPENGLSCENEEXAMPLE_H

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OpenGLScene.zip

[tbscope]

Your problem is the use of m_pOGLObject and gl...list functions.

I don't know enough of OpenGl to help you with that. But I guess switching displays inside the paint function is the problem (if that is what glCallList does)