qt - Zoom in scaled down QPixmap: can't restore original size -

i making application need draw figures (i.e. rectangles) above picture , resize whole scene. i'm using qgraphicsview , qgraphicsscene. can't figure out why when using fitintoview() unable draw figures on top of picture (they drawn behind picture or outside bounds).

now i'm using qpixmap.scaled() make image fit in qgraphicsscene. works fine except when need display big image , zoom in. because scaled image fit, became smaller , when call qgraphicsview.scale() image scales small 1 , can't find way "scale back" image original size.

in zoom part of code tried replace pixmap not scaled copy can't scale same proportions figures scaling. appreciated!

---

here load image , scale it

qpixmap pix; pix = pixmap->scaled(wid, hei,qt::keepaspectratio, qt::smoothtransformation); scn = new qgraphicsscene(pw); pw->setscene(scn); p = new qgraphicspixmapitem(pix); p->setpixmap(pix); scn->additem(p); 

i draw figures this

rect = new qgraphicsrectitem(x,y,w,h); rect->setpen(qpen(getcolor(), 1, qt::solidline, qt::flatcap)); scn->additem(rect); 

and here's how zoom

pw->scale(scalefactor_,scalefactor_); 

---

update: have qwidget kind of toolbar on top, rest of free space filled custom qgraphicsview. derived class grabbing mouse events, there's nothing more overrides of event handlers. i'm adding paintergraphicsview in widget's constructor:

pw = new paintergraphicsview(); ui->gridlayout_3->addwidget(pw); 

i'm recreating scene every time load new image it:

scn = new qgraphicsscene(pw); pw->setscene(scn); qrect r = qrect(0,0, pw->width()-5, pw->height()-5); scn->setscenerect(r); 

after loaded image can draw figures on top of it, looks this:

and scaled contents this:

as can see, figures scaled pixmap , how need work. thing have fix low quality of scaled pixmap. said, tried replace pixmap original 1 in zoomin method, can't saving figures' position.

void drawerwidget::on_btzoom_clicked() {     p->setpixmap(pix); //p qgraphicspixmapitem, pix original pixmap     p->setscale(0.5); //how can scale pixmap figures?? how calculate required scale?     pw->scale(scalefactor_,scalefactor_); } 

---

update 2:

a short explanation on drawing figures method: (though don't think issue, i'm interested there way scale qgraphicspixmapitem using setscale() fit in qgraphicsview size)

i'm getting start_ , end_ coordinates mouse events arguments (qmouseevent *e)

 end_=pw->maptoscene(e->pos());  start_=pw->maptoscene(e->pos()); 

i add figure on mousepress:

rect = new qgraphicsrectitem(start_.x(),start_.y(),1,1); scn->additem(rect); 

and redraw figure on mouse move

rect->setrect(graphics::getfigure(start_.x(),start_.y(),end_.x(),end_.y())); 

getfigure method calculating figure's rect, here's main part of it:

 static qrectf getfigure(double startx, double starty, double finalx, double finaly)     {       qrectf shape;       shape.setx(startx);       shape.sety(starty);       shape.setwidth(qfabs(finalx - startx));       shape.setheight(qfabs(finaly - starty));       return shape;    } 

the scaling operation destructive, once scale down end less data started with.

if want able restore original size keep copy of original pixmap.

you can create qgraphicspixmapitem original, non-scaled pixmap , use qgraphicspixmapitem::setscale(qreal) change size on level graphics item, not on level pixmap data. way scaling should not destructive, , should not lose quality if scale original size.

if want scale multiple items (and not run different transformation origin problems) have few options:

• scale entire view - scale everything
• add items children of parent item, scaling parent scale children well

item transformations accumulate parent child

• add items group using createitemgroup():

the items reparented group, , positions , transformations mapped group