qgraphicsview and coordinates
I am trying to use a qgraphicsview as part of a plotting app. There are two graphs, one above the other that are aligned with the x-axis extents. I have axes around a center widget, in the lower instance it uses a simple qwidget and in upper, it uses a qgraphicsview.
My problem comes in lining up the axes extents to the extents inside of the qgraphicsview. For example, my X-axis runs from 2000000 to 30000000 and my Y-axis from 3600 to 90000. I call setSceneRect with these values and then call a modified fitInView (modified to remove the hard-coded margin of 2 adjustment). The sceneRect shows the proper (2000000,3600 28000000x86400). However, if I try to do mapToScene( QPoint(0,0) ), I do not get (2000000,3600) that I expect but values slightly off (1971830.985915, 3578.698225), so qgraphicsview does not quite line up with values of the axes. If I put a qgraphicslineitem vertically at 20000000, it does not draw in the proper location wrt x-axis. I know this seems negligible but with a crosshair cursor that displays the x,y values with the cursor position based on the axis, it just looks wrong. And it does not line up with a similar vertical line and similar crosshair cursor in the qwidget that uses transform routines based on the axes.
Is there a way to tweak the matrix/transform so the qgraphicsview coordinates match closer to my axis scaling?
Re: qgraphicsview and coordinates
why are you making your own plotting app? there is already qwt.
btw, it will be your maths/mapping that is making something not quite match. Trying to fudge it with a Qt transform will just move the error somewhere else.
Re: qgraphicsview and coordinates
Quote:
Originally Posted by
amleto
why are you making your own plotting app? there is already qwt.
It is an app at work that is unique to the data set.
Quote:
btw, it will be your maths/mapping that is making something not quite match. Trying to fudge it with a Qt transform will just move the error somewhere else.
The qwidget plotting canvas is controlled by the x/y axes . . . simple math to get the mapping. I assumed setting the same x/y ratios in the qgraphicsview would use the same scaling. I guess the fit in view is not producing the affect I expect. The initial setting seems to set the view outside my initial screenRect. How do I set the qgraphicsview to a specific X,Y WxH? Specific meaning that the viewport (0,0) = X,Y and viewport (xmax,ymax) = X+W,Y+H
I know that pixel on the screen can take on a number of values depending on the resolution of the widget. I just want to be able to specific what those "real" values are for the left,right and top,bottom edges of the qgraphicsview like I do with the qwidget.
