c++ - An issue when rendering a line depending on Mouse position -

i have opengl widget, want render line dependent of mouse positions, follows:

        glpushmatrix();         glenable(gl_blend);         glblendfunc(gl_src_alpha, gl_one_minus_src_alpha);         glcolor4f(1, 0, 0, 0.1);         glscalef(a, b, 0);         glbegin(gl_lines);         glvertex2f(pushedx, pushedy);         glvertex2f(currentx, currenty);         glend();         glflush();         gldisable(gl_blend);         glpopmatrix(); 

where:

pushedx=buttonpresscoordinates.x(); pushedy=buttonpresscoordinates.y(); currentx=mousecurrentposition.x(); currenty=mousecurrentposition.y(); 

the rendering goes good, , line rendered required when move mouse connecting line pushed , current coordinates.

but:

the issue is, when press mouse somewhere on widget , don't move it, generates randomly (as think) (x,y) , connects line coordinates of mouse pressed position. though when start moving mouse starts working fine.

please, fix bug.

edit

the code of assigning current values of mouse

void mainwindow::mousemoveevent(qmouseevent *eventmove) {     if(eventmove->buttons() & qt::leftbutton)     {         glwidget *widget = this->findchild<glwidget *>("glwidget");         float x = widget->getnormalizedwidth(widget->mapfromglobal(qcursor::pos()).x());         float y = widget->getnormalizedheight(widget->mapfromglobal(qcursor::pos()).y());         float y_ = 1.0 - y;         mousecurrentposition.setx(x);         mousecurrentposition.sety(y_);         widget->setcurrentx(mousecurrentposition.x());         widget->setcurrenty(mousecurrentposition.y());     } } 

note: qpointf mousecurrentposition;, getnormalizedwidth(...) defined fundction works perfect.

edit-2

the mouse click coordinates updated follows:

setmousetracking(true); m = true; glwidget *widget = this->findchild<glwidget *>("glwidget"); float x = widget->getnormalizedwidth(widget->mapfromglobal(qcursor::pos()).x()); float y = widget->getnormalizedheight(widget->mapfromglobal(qcursor::pos()).y()); float y_ = 1.0 - y; buttonpresscoordinates.setx(x); buttonpresscoordinates.sety(y_); qdebug() << buttonpresscoordinates.x() << buttonpresscoordinates.y(); widget->setq(true); widget->setpushedx(buttonpresscoordinates.x()); widget->setpushedy(buttonpresscoordinates.y()); 

one thing can try update currentx , currenty in mousemoveevent when leftbutton not pressed:

void mainwindow::mousemoveevent(qmouseevent *eventmove) {       glwidget *widget = this->findchild<glwidget *>("glwidget");      float x = widget->getnormalizedwidth(widget->mapfromglobal(qcursor::pos()).x());      float y = widget->getnormalizedheight(widget->mapfromglobal(qcursor::pos()).y());      float y_ = 1.0 - y;      if(eventmove->buttons() & qt::leftbutton)     {               buttonpresscoordinates.setx(x);         buttonpresscoordinates.sety(y_);               widget->setpushedx(buttonpresscoordinates.x());         widget->setpushedy(buttonpresscoordinates.y());     }     else     {         mousecurrentposition.setx(x);         mousecurrentposition.sety(y_);         widget->setcurrentx(mousecurrentposition.x());         widget->setcurrenty(mousecurrentposition.y());     } }