Re: TPad::Update (was: Object lifetime/scope connected to TFile)

From: Valeri Fine (Faine) (fine@bnl.gov)
Date: Wed Sep 08 1999 - 16:08:42 MEST


ones.) 
> 
> It turned out that one has to call Modified(1) of the canvas in which the
> Histogram appears. In command-line mode, this result in an automatical
> update of the canvas, since the Update() methods of the canvases are called
> after execution of each line. I can image the want for the Modified flag
> for object which are IN the canvas, but for the canvas itself this seems a
> bit strange, since the call MyCanvas->Modified(1) apparently (ALWAYS) needs
> to proceed a call to MyCanvas->Update(), to force the update of the canvas.
> I don't know about the technicalities, but I would propose to either set
> the Modified flag of a canvas to kTRUE every time something in the canvas
> is modified or to arrange that a call to Update always checks the Modified
> flags of the drawn objects (regardless of the Modified-flag of the canvas).
> 
> Does anyone disagree???

  Nobody agrees. 

   - It is not essential to call Update() next line one calls Modified()

   - One can modify TCanvas / TPad as many times as he things he does modify and call
    Update as soon as one decides  it is time to refresh the images of the modified TCanvas's
   / TPad's  on the real screen.

 - One and the same object can be present with as many TCanvas / TPad as the user finds 
   useful for his/her  jobs.

 - Framework has no control over the user supplied object and should not CHANGE user's object.
   Framework can modify only objects it owns, namely TCanvas's / TPad and can not touch the user's
   objects like histograms. Framework should not assume drawn object can hold his "modified" status.
   Anyway this doesn't help with multi-pad representation of one and the same object. If one has lets' say
   two TPad with different view of one and the same user's object and one does update one TPad with that,
   did one "clean" that "modified" flag of my object or not.


   There are other reasons as well. . . 

                      Valery



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