[RQt-devel] possible bug in qtbase

[Michael Lawrence]

On Tue, Sep 20, 2011 at 7:40 PM, Deepayan Sarkar
<deepayan.sarkar at gmail.com>wrote:

> On Wed, Sep 21, 2011 at 3:20 AM, Michael Lawrence
> <lawrence.michael at gene.com> wrote:
> >
> >
> > On Tue, Sep 20, 2011 at 12:03 PM, Deepayan Sarkar
> > <deepayan.sarkar at gmail.com> wrote:
> >>
> >> On Tue, Sep 20, 2011 at 8:55 PM, Michael Lawrence
> >> <lawrence.michael at gene.com> wrote:
> >> > Hi Deepayan,
> >> >
> >> > Nice to hear you are back into the Qt stuff. I can indeed reproduce
> >> > this.
> >> > But not anymore, because I've fixed it.
> >>
> >> Thanks, I can confirm the fix.
> >>
> >> I've decided to try out a different approach, managing the layout in R
> >> as much as possible, and target multiple backends. I'm initially
> >> experimenting with QGraphicsView/Scene, and now I'm getting much
> >> further with that thanks to your fix. At some point I'll start bugging
> >> you about qtpaint as well.
> >>
> >
> > You might want to check out anypaint in the GGobi github. Gabriel Becker
> > (DTL's student) has been doing a lot of work on generic (pure R, backend
> > agnostic) implementations of things like layout. He's implementing
> anypaint
> > against HTML5/JS in Firefox, via RFirefox. I need to make sure that he is
> > committing his stuff back into github.
>
> Seems mostly notImplemented() calls right now.
>
>
Right, it's just the abstraction. Gabe's firepaint package implements it for
RFirefox. qtpaint will implement it for Qt.


> >> I think there are still problems lurking around. Here is a protection
> >> bug: This gives an error because the gc() causes view$scene() to go
> >> away.
> >>
> >> ----
> >> library(qtbase)
> >>
> >> view <- Qt$QGraphicsView()
> >> view$size <- qsize(600, 600)
> >> view$setScene(Qt$QGraphicsScene())
> >> ## class(view$scene())
> >> gc()
> >> view$scene() # NULL
> >> view$scene()$clear()
> >> ----
> >>
> >> If I uncomment the 'class(view$scene())' then things are OK.
> >>
> >
> > This is just Qt. Neither R nor QGraphicsView keep a reference to the
> scene.
> > This is why qtpaint sets the parent of the scene to the view, if it does
> not
> > already have a parent.
>
> So having an R reference like so
>
> scene <- Qt$QGraphicsScene()
> view$setScene(scene)
>
> should be safe?
>
>
Yes, but I would recommend setting the parent, so that you do not need to
worry about the R reference. That's sensible as long as you have a single
view.


> >> In a more realistic example involving QGraphicsScene (that I haven't
> >> been able to simplify yet), having a gc() keeps things sane, and not
> >> having it leads to errors similar to the ones before, e.g.,
> >>
> >> Error in qinvokeStatic(cl, basename, ...) :
> >>  Expected an instance of type 'QColor', not 'QGraphicsLineItem'
> >> Calls: print ... is -> qbrush -> <Anonymous> -> qinvokeStatic -> .Call
> >>
> >
> > Looking forward to that simplified example.
>
> Here goes. Adding the gc() makes the whole thing work fine. The
> trivial qpen() call is required.
>
>
Thanks a lot. Will look at this.


> #----
> library(qtbase)
>
> v <- Qt$QGraphicsView()
> v$size <- qsize(300, 300)
> scene <- Qt$QGraphicsScene()
> v$setScene(scene)
> v$show()
>
> doplot <- function(view, scene)
> {
>    ## gc()
>    scene$clear()
>    x <- runif(2, 50, 250)
>    scene$addEllipse(x[1], x[2], 10, 10, qpen())
>    Sys.sleep(0.01)
> }
>
> niter <- 0L
> while (TRUE)
> {
>    doplot(view = v, scene = scene)
>    niter <- niter + 1
>    cat(niter, fill = TRUE)
> }
> #----
>
> I'm usually getting an error within 10 iterations.
>
> -Deepayan
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.r-forge.r-project.org/pipermail/qtinterfaces-devel/attachments/20110920/c41cc7b3/attachment-0001.htm>