Hi Valery,
As already reported a few times, the solution to this problem
is the new image processing class TASImage that has been introduced
in the version 3.03/09. Reiner Rohlfs will present this class
and demos at the coming ROOT workshop.
Rene Brun
On Mon, 30 Sep 2002, Valeri Fine wrote:
> Hello Ed,
>
> Thank you very much for the working example you sent me.
> It made things much simpler to investigate.
> Sorry for some delay.
> I have investigated your code.
>
> > you able to duplicate the problem I was having (e.g. cpu time required
> to
> > redraw scatter plot grows as histogram gets more entries)?
>
> Yes I did.
>
> However your observation is not correct. It does grow but by the point.
> Your 2D histogram is 500 x 500 bins = 250 000 bins.
> Just try to define 50 x 50 to see what I am speaking about.
> If you will define 100 x 100 you will realize the refresh time is
> growing but it quickly becomes constant.
> In fact the refresh time of 2D histogram should be proportional (at
> least) to the number of non-zero cells of your 2D histogram. Since the
> number of your non-zero cells is growing that refresh rate is going
> down.
>
> I think the better performance can be provided via
> TVirtualX::DrawCellArray.
> However ROOT doesn't use it. This means each non-zero bin is drawn with
> several dedicated calls to the low level graphics layer. That must slow
> things down significantly. Each bin is drawn as colored box. This means
> to draw it the program has to set the current color pen and color brush
> and then draw the filled box. To accomplish this it needs to call the
> TVirtualX layer several times. To make things ever worse the low level
> layer is called via 2 other intermediate layers.
>
>
> See:
> http://root.cern.ch/root/htmldoc/src/THistPainter.cxx.html#THistPainter:
> PaintColorLevels
>
> In you case to refresh the picture ROOT calls up to 250'000 times:
>
> fH->SetFillColor(gStyle->GetColorPalette(theColor));
> fH->TAttFill::Modify();
> gPad->PaintBox(xlow, ylow, xup, yup);
>
> You can see the algorithm of the THistPainter works well if the
> occupancy of the cells is not high because it skips the empty cells. It
> must degrade as soon as the occupancy of the cells grows (that's your
> case)
>
> > > Is there something I could do to speed things up, short of adjusting
> the
> > > refresh rate? I am using version 3.03/08 on Win32. Thanks...
>
> At this point it would be reasonable to see whether you can use
> TVirtualX::DrawCellArray methods. That will do everything in a single
> call.
> Be this reason one may expect the refresh time will be steady.
> However this approach requires the custom THistPainter::PaintColorLevels
>
> method to be introduced.
>
> > Note 2: In addition to the 2D histogram, I also have a couple
> > of 1-D histograms. [The object to display/update is selected
> > at runtime. All objects are filled all the time] The 1D
> > histograms updating never slows down, only the 2D histograms
>
> As I have explained the time to re-draw the histogram depends of the
> number of the bins to be drawn,
> Your 1D histogram contains 600 bins. This is nothing against of
> 250'000 bins of your 2D histogram.
>
> Hope this helps. My best regards, Valeri
>
>
>
> > -----Original Message-----
> > From: Ed Oltman [mailto:eoltman@imago.com]
> > Sent: Tuesday, September 03, 2002 9:35 AM
> > To: fine@bnl.gov; 'Roottalk@Pcroot. Cern. Ch'
> > Subject: RE: [ROOT] Performance question: Updating a colz histogram
> >
> > Valeri,
> > Here are some more details (not in order asked)
> >
> > 2. I had the same problem in V 3.02/7 as well as 3.03/8
> >
> > 4. I am using a standalone root based application - e.g. I
> > create an instance of TRint. The application is an MFC
> > SDI application where I took special pains to wrap the
> > root stuff in its own class that does not have #include
> > "stdafx.h" or any other windows/mfc stuff.
> >
> > 1. My application's view class has an OnTimer() method
> > which in turn calls p2DH->Draw("colz") and
> > gPad->GetCanvas()->Update().
> >
> > 3. If you like, I could make a small mfc project that
> > displays the problem I'm having.
> >
> > Note: you mention in subsequent e-mail that it is not
> > necessary to call the Draw() method each time. If I do
> > not call the Draw() method each time, nothing gets displayed.
> >
> > Note: The histogram is filled in a different thread than
> > it is displayed. I use a win32 semaphore to protect the
> > object's filling with its display.
> >
> > Note 2: In addition to the 2D histogram, I also have a couple
> > of 1-D histograms. [The object to display/update is seleceted
> > at runtime. All objects are filled all the time] The 1D
> > histograms updating never slows down, only the 2D histograms
> >
> > Ed Oltman
> >
> > > -----Original Message-----
> > > From: Valeri Fine [mailto:fine@bnl.gov]
> > > Sent: Friday, August 30, 2002 5:31 PM
> > > To: 'Ed Oltman'; 'Roottalk@Pcroot. Cern. Ch'
> > > Subject: RE: [ROOT] Performance question: Updating a colz histogram
> > >
> > >
> > > Hello Ed,
> > > Sorry, you didn't send an example to reproduce your troubles so I
> have
> > > to ask you some extra questions:
> > >
> > > 1. What kind of timer do you use: synch or asynch ?
> > > 2. Did you see this problem before (with the previous version of
> > > ROOT) ?
> > > 3. Can you work out a small macro / code to reproduce the problem
> ?
> > > 4. Do you use "ROOT + macro"; "Root + your custom DLL"; your
> > > ROOT-based application alone ?
> > >
> > > Thank you
> > > Valeri
> > >
> > > -----Original Message-----
> > > From: owner-roottalk@pcroot.cern.ch
> > > [mailto:owner-roottalk@pcroot.cern.ch] On Behalf Of Ed Oltman
> > > Sent: Friday, August 30, 2002 5:35 PM
> > > To: Roottalk@Pcroot. Cern. Ch
> > > Subject: [ROOT] Performance question: Updating a colz histogram
> > >
> > > Hello,
> > > I have an online application which includes a 500x500 bin TH2F
> which I
> > > display in response to a timer with
> > >
> > > p2DH->Draw("colz");
> > > gPad->GetCanvas()->Update();
> > >
> > > (I've previously called gStyle->SetPalette(1,0)) Early on, when the
> > > histogram is still young, the refresh is pretty quick - refreshing
> at 2
> > > Hz
> > > uses a small amount (<10%) of the cpu time. Gradually, as the
> histogram
> > > fills, the refresh time increases - by the time the histogram has a
> few
> > > hundred thousand entries, (maximum bin contents is in the 10s) the
> cpu
> > > time
> > > is 80% and climing.
> > >
> > >
> > > Ed Oltman
> > >
> > >
> > >
> > >
> > >
>
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