3 Dimensions using opengl

[vermarajeev]

Can't you simply draw them on QGLWidget once in 2D and once in 3D?

No! Basically the user has an option to draw in 2D and view the result in 3D. If I need to use QGLWidget for both 2D and 3D then I'll have so much of rework to do. Is it not possible to use what is already existing?
Something like Just send the graphicsView object to QGLwidget and let it draw using opengl APIs.

Waiting eagerly.
Thanks

[fullmetalcoder]

Something like Just send the graphicsView object to QGLwidget and let it draw using opengl APIs.

This is not a bad idea if you know how to handle the OpenGL-based 3D drawing but consider using the QGraphicsScene object instead.

[vermarajeev]

This is not a bad idea if you know how to handle the OpenGL-based 3D drawing but consider using the QGraphicsScene object instead.

Jacek--> Can you please tell me how do I use QTranform as specified in the link above in qt4.2.2. I think QTranform should make work easier.

fullmetalcoder--> I have written a sample program can you please help me to represent a 2D object to 3D.

//GraphicsView

graphicsView::graphicsView(QGraphicsScene* s, QWidget *parent)
	: QGraphicsView(s, parent), m_scene(s){	
	s->setItemIndexMethod(QGraphicsScene::NoIndex);
    s->setSceneRect(-200, -200, 400, 400);
 
	QPushButton* btnOPenGl = new QPushButton("OpenGL", this);
	btnOPenGl->setGeometry( 300, 300, 50, 30 );
	connect( btnOPenGl, SIGNAL( clicked() ), this, SLOT( onbtnOPenGlClick() ) ); 
}
 
graphicsView::~graphicsView()
{}
 
void graphicsView::onbtnOPenGlClick(){
	GLWidget* GLwid = new GLWidget(this);
	GLwid->show();
}
 
void graphicsView::drawBackground(QPainter *painter, const QRectF &rect){
     Q_UNUSED(rect);	 
	 paint(painter);
 }
void graphicsView::paint(QPainter* painter){
	static const QPoint points[6] = {
         QPoint(-30, -20),
         QPoint(-70, 30),
         QPoint(-30, 80),
         QPoint(30, 80),
		 QPoint(70, 30),
		 QPoint(30, -20)		 
     };	
	painter->drawPolygon(points, 6);	
}

graphicsView::graphicsView(QGraphicsScene* s, QWidget *parent)
	: QGraphicsView(s, parent), m_scene(s){	
	s->setItemIndexMethod(QGraphicsScene::NoIndex);
    s->setSceneRect(-200, -200, 400, 400);

	QPushButton* btnOPenGl = new QPushButton("OpenGL", this);
	btnOPenGl->setGeometry( 300, 300, 50, 30 );
	connect( btnOPenGl, SIGNAL( clicked() ), this, SLOT( onbtnOPenGlClick() ) ); 
}

graphicsView::~graphicsView()
{}

void graphicsView::onbtnOPenGlClick(){
	GLWidget* GLwid = new GLWidget(this);
	GLwid->show();
}

void graphicsView::drawBackground(QPainter *painter, const QRectF &rect){
     Q_UNUSED(rect);	 
	 paint(painter);
 }
void graphicsView::paint(QPainter* painter){
	static const QPoint points[6] = {
         QPoint(-30, -20),
         QPoint(-70, 30),
         QPoint(-30, 80),
         QPoint(30, 80),
		 QPoint(70, 30),
		 QPoint(30, -20)		 
     };	
	painter->drawPolygon(points, 6);	
}

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//QGLWidget

#include <QGLWidget>
#include "graphicsview.h"
 
class graphicsView;
class GLWidget : public QGLWidget
{
public:
	GLWidget(graphicsView* gv, QWidget *parent=0 ) 
		: QGLWidget( parent ), m_graphicsView(gv)
	{}
 
protected:
	void paintEvent( QPaintEvent* event ){
		QPainter paint;
		paint.begin(this);
		m_graphicsView->paint(&paint);
		paint.end();
	}
	/*void initializeGL()
	{
		glShadeModel(GL_SMOOTH);
 
		glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
		glClearDepth(1.0f);
 
		glEnable(GL_DEPTH_TEST);
		glDepthFunc(GL_LEQUAL);
 
		glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
	}	
	void resizeGL( int width, int height )
	{
  		height = height?height:1;
 
		glViewport( 0, 0, (GLint)width, (GLint)height );
 
		glMatrixMode(GL_PROJECTION);
		glLoadIdentity();
		gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);
 
		glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();
	}	
	void paintGL()
	{
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glLoadIdentity();
 
		glTranslatef(-1.5f,0.0f,-6.0f);
 
		glBegin(GL_TRIANGLES);
			glVertex3f( 0.0f, 1.0f, 0.0f);
			glVertex3f(-1.0f,-1.0f, 0.0f);
			glVertex3f( 1.0f,-1.0f, 0.0f);
		glEnd(); 				
	}*/
private:
	graphicsView* m_graphicsView;
};

#include <QGLWidget>
#include "graphicsview.h"

class graphicsView;
class GLWidget : public QGLWidget
{
public:
	GLWidget(graphicsView* gv, QWidget *parent=0 ) 
		: QGLWidget( parent ), m_graphicsView(gv)
	{}
	
protected:
	void paintEvent( QPaintEvent* event ){
		QPainter paint;
		paint.begin(this);
		m_graphicsView->paint(&paint);
		paint.end();
	}
	/*void initializeGL()
	{
		glShadeModel(GL_SMOOTH);

		glClearColor(0.0f, 0.0f, 0.0f, 0.0f);
		glClearDepth(1.0f);

		glEnable(GL_DEPTH_TEST);
		glDepthFunc(GL_LEQUAL);

		glHint(GL_PERSPECTIVE_CORRECTION_HINT, GL_NICEST);
	}	
	void resizeGL( int width, int height )
	{
  		height = height?height:1;

		glViewport( 0, 0, (GLint)width, (GLint)height );

		glMatrixMode(GL_PROJECTION);
		glLoadIdentity();
		gluPerspective(45.0f,(GLfloat)width/(GLfloat)height,0.1f,100.0f);

		glMatrixMode(GL_MODELVIEW);
		glLoadIdentity();
	}	
	void paintGL()
	{
		glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
		glLoadIdentity();

		glTranslatef(-1.5f,0.0f,-6.0f);

		glBegin(GL_TRIANGLES);
			glVertex3f( 0.0f, 1.0f, 0.0f);
			glVertex3f(-1.0f,-1.0f, 0.0f);
			glVertex3f( 1.0f,-1.0f, 0.0f);
		glEnd(); 				
	}*/
private:
	graphicsView* m_graphicsView;
};

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Thanks

[minimoog]

What kind of 2D objects do you want to represent with 3D version?

[jacek]

Can you please tell me how do I use QTranform as specified in the link above in qt4.2.2. I think QTranform should make work easier.

If I understand your problem correctly, QTransform won't help you --- after you apply QTransform your object still will be flat.

[minimoog]

Lines in 2D can be represented in 3D with simple lines or cylinder.

For simple lines you can use glBegin(GL_LINES), glBegin(GL_LINESTRIP) or glBegin(GL_LINE_LOOP).

glBegin(GL_LINE_STRIP);
glVertex2f(from_x, from_y);
glVertex2f(to1_x, to1_y);
glVertex2f(to2_x, to2_y);
....
glEnd();

glBegin(GL_LINE_STRIP);
glVertex2f(from_x, from_y);
glVertex2f(to1_x, to1_y);
glVertex2f(to2_x, to2_y);
....
glEnd();

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This will draw simple connected line, which can be easily rotated.

[vermarajeev]

Lines in 2D can be represented in 3D with simple lines or cylinder.

For simple lines you can use glBegin(GL_LINES), glBegin(GL_LINESTRIP) or glBegin(GL_LINE_LOOP).

glBegin(GL_LINE_STRIP);
glVertex2f(from_x, from_y);
glVertex2f(to1_x, to1_y);
glVertex2f(to2_x, to2_y);
....
glEnd();

glBegin(GL_LINE_STRIP);
glVertex2f(from_x, from_y);
glVertex2f(to1_x, to1_y);
glVertex2f(to2_x, to2_y);
....
glEnd();

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This will draw simple connected line, which can be easily rotated.

So you mean to say, I need to redraw the objects again in 3D.
Actually I dont want to redraw the things again.
Anyway since I'm not able to get the what I want I should atleast see how your logic works. Can you please help me to achieve what you have suggested in the above sample program that I have posted.

Thanks

[jacek]

Actually I dont want to redraw the things again.

It won't happen all by itself. It's much easier to simply draw that molecule again in 3D than convert a 2D image to 3D one. First you need some kind of a representation, for example a set of segments. Then you can draw it in whatever form you like.

[minimoog]

Well, you have to draw it again.

QPainter when is using OpenGl is doing the similar thing like in my code example. It's just sends triangles to opengl using orthographic projection. But you cannot access QPainter OpenGL projection and modelview matrix (of course, you can change the source code if you want it), so you must redraw in 3D all that stuff. That's why I asked you what kind of 2D objects you want to represent in 3D.

void paintGL()
{
 
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
 
static const QPoint points[6] = {
  QPointF(-3, -2),
  QPointF(-7, 3),
  QPointF(-3, 8),
  QPointF(3, 8),
  QPointF(7, 3),
   QPointF(3, -0) }; 
 
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
 
glTranslatef(0.0, 0.0, -5.0);
 
glBegin(GL_LINE_LIST);
 
for(int i = 0 ; i < 6; i++){
 glVertex2f(points[i].x, points[i].y);
}
 
glEnd();
}

void paintGL()
{

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

static const QPoint points[6] = {
  QPointF(-3, -2),
  QPointF(-7, 3),
  QPointF(-3, 8),
  QPointF(3, 8),
  QPointF(7, 3),
   QPointF(3, -0) }; 

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

glTranslatef(0.0, 0.0, -5.0);

glBegin(GL_LINE_LIST);

for(int i = 0 ; i < 6; i++){
 glVertex2f(points[i].x, points[i].y);
}

glEnd();
}

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Maybe there are some errors...

[vermarajeev]

It won't happen all by itself. It's much easier to simply draw that molecule again in 3D than convert a 2D image to 3D one. First you need some kind of a representation, for example a set of segments. Then you can draw it in whatever form you like.

Ok Here is the class representation of 2D objects drawn on QGraphicsView.

class DrawMolecule : public ChemObject
{}
class DrawAtom : public ChemObject
{}//
class DrawBond : public ChemObject
{}//

class DrawMolecule : public ChemObject
{}
class DrawAtom : public ChemObject
{}//
class DrawBond : public ChemObject
{}//

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Here ChemObject is a pure Virtual class inherited from QObject which provides an interface to draw an atom, bonds. The combination of atoms and bonds forms a molecule.
Jacek I think you were talking about this. Please suggest.

minimoog--> Thanks for your sample program but there are some errors as you mentioned. M trying to rectify. Thanks again

Jacek, you are a multitasking human being (really good at chemistry too). Fabulous!!!

[jacek]

Jacek I think you were talking about this.

Yes, now you have to add routines that will draw each of those objects. Take a look at gluSphere() and gluCylinder() functions.

You can add QGraphicsView and QGLWidget to QStackedWidget, so you can switch between the 2D and 3D view easily.

[vermarajeev]

Yes, now you have to add routines that will draw each of those objects. Take a look at gluSphere() and gluCylinder() functions.

You can add QGraphicsView and QGLWidget to QStackedWidget, so you can switch between the 2D and 3D view easily.

Hi jackek,
Thanks for your suggestions. I'll take a look at those examples and see how I can solve the problem. Thanks a lot. Will keep you updating.

Thanks

[vermarajeev]

Hi Jacek,
I did a sample program to convert 2D to 3D. I have not used any representation but just a sample. I'll make use of DrawAtom, DrawBond and DrawMolecule classes once I'm perfect with what I have to do. Anyway below is the code. Please tell me if I'm going anywhere wrong. Also when I draw two or more polygons, they are not displayed in exact positions as they appear in 2D.

I have a zipped file.

Steps to follow once the progrma is executed:
1) Click on 'Draw Poly'.
2) Release the mouse on GraphicsView. It will draw a polygon. If you want two or more
polygon then again click 'Draw Poly' and then release mouse and so on.
3) Once there are polygons on GraphicsView click 'opengl' to get the 3D View.

Please help me to improve my code. Also the positions of polygons in 3D are not same as 2D
Thanks

[pdolbey]

I've put the QGraphicsView/Scene into a consistent coordinate system with OpenGL i.e.

Y
^
|
+---> X

I've switched you to a orthographic projection - always better for scientific stuff. The OpenGL viewport coordinates are mapped to the scenegraph, and I've changed the graphics object to use a 2:1 ratio triangle - much easier to see the mappings with this.

Seems to work.

Pete