drag and drop and Co. with openGL and Qt - qt

Question

I am trying to write a 2D application with openGL (do not ask why, it a test for a stage) where I have a texture I can move around with a drag and drop, rotate or scal with the mouse. My texture is applied on a square.
For these operations, I need to know if I am clicking on the polygon, and the distance and angle between my cursor and the polygon center (which can be moved).
I did not find how to do these with the tutorial I am following does not cover that.
How can I find those 2 informations?
Here is the code :
#include "glwidget.h"
#include <QMouseEvent>
#include <QKeyEvent>
#ifdef WIN32
#include <GL/glext.h>
PFNGLACTIVETEXTUREPROC pGlActiveTexture = NULL;
#define glActiveTexture pGlActiveTexture
#endif //WIN32
GlWidget::GlWidget(QWidget *parent) :
QGLWidget(QGLFormat(), parent)
{
}
GlWidget::~GlWidget(){}
QSize GlWidget::sizeHint() const
{
return QSize(640,480);
}
void GlWidget::resizeGL(int w, int h){
h = (h<=0?1:h);
pMatrix.setToIdentity();
pMatrix.perspective(60.0,(float)w /(float)h,0.1,10);
glViewport(0,0,w,h);
//glScissor(w*0.8,0,w*0.2,h);
//glDisable(GL_SCISSOR_TEST);
}
void GlWidget::initializeGL(){
#ifdef WIN32
glActiveTexture = (PFNGLACTIVETEXTUREPROC) wglGetProcAddress((LPCSTR) "glActiveTexture");
#endif
glEnable(GL_DEPTH_TEST);
glEnable(GL_CULL_FACE);
qglClearColor(QColor(Qt::black));
shaderProgram.addShaderFromSourceFile(QGLShader::Vertex, ":/vertexShader.vsh");
shaderProgram.addShaderFromSourceFile(QGLShader::Fragment, ":/fragmentShader.fsh");
shaderProgram.link();
vertices << QVector3D(-1,-1,-2) << QVector3D(1,-1,-2) << QVector3D(-1,1,-2)
<< QVector3D(-1,1,-2) << QVector3D(1,-1,-2) << QVector3D(1,1,-2);
textureCoordinates << QVector2D(0, 0) << QVector2D(1, 0) << QVector2D(0, 1)
<< QVector2D(0, 1) << QVector2D(1, 0) << QVector2D(1, 1);
texture = bindTexture(QPixmap(":/icone.png"));
//mMatrix.setToIdentity();
}
void GlWidget::paintGL(){
//qglClearColor(QColor(Qt::white));
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
/*qglClearColor(QColor(Qt::black));
glScissor(this->width()*0.8,0,this->width()*0.2,this->height());
glEnable(GL_SCISSOR_TEST);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glDisable(GL_SCISSOR_TEST);*/
QMatrix4x4 mMatrix;
QMatrix4x4 vMatrix;
/* QMatrix4x4 cameraTransformation;
cameraTransformation.rotate(25, 0, 1, 0);
cameraTransformation.rotate(-25, 1, 0, 0);
QVector3D cameraPosition = cameraTransformation * QVector3D(0, 0, 2.5);
QVector3D cameraUpDirection = cameraTransformation * QVector3D(0, 1, 0);
vMatrix.lookAt(cameraPosition, QVector3D(0, 0, 0), cameraUpDirection);*/
shaderProgram.bind();
shaderProgram.setUniformValue("mvpMatrix", pMatrix*vMatrix*mMatrix);
shaderProgram.setUniformValue("texture", 0);
glActiveTexture(GL_TEXTURE0);
glBindTexture(GL_TEXTURE_2D, texture);
glActiveTexture(0);
shaderProgram.setAttributeArray("vertex", vertices.constData());
shaderProgram.enableAttributeArray("vertex");
shaderProgram.setAttributeArray("textureCoordinate", textureCoordinates.constData());
shaderProgram.enableAttributeArray("textureCoordinate");
glDrawArrays(GL_TRIANGLES,0,vertices.size());
shaderProgram.disableAttributeArray("vertex");
shaderProgram.disableAttributeArray("textureCoordinate");
shaderProgram.release();
}
void GlWidget::mousePressEvent(QMouseEvent *event){
if(event->button()==Qt::LeftButton)
lastPos = event->pos();
event->accept();
}
void GlWidget::mouseMoveEvent(QMouseEvent *event){
if(!event->buttons().testFlag(Qt::LeftButton)) return;
int dx = event->x() - lastPos.x();
int dy = event->y() - lastPos.y();
if(keysPressed.contains(Qt::Key_Control) && !keysPressed.contains(Qt::Key_Shift)){
//TODO : implement scaling
}
else if(!keysPressed.contains(Qt::Key_Control) && keysPressed.contains(Qt::Key_Shift)){
//TODO : implement rotate
}
else if(!keysPressed.contains(Qt::Key_Control) && !keysPressed.contains(Qt::Key_Shift)){
//TODO : implement drag
}
}
void GlWidget::keyPressEvent(QKeyEvent *event){
keysPressed.append(event->key());
}
void GlWidget::keyReleaseEvent(QKeyEvent *event){
keysPressed.remove(keysPressed.lastIndexOf(event->key()));
}
All the comments are from test I've done and the original tutorial