By the way, I just did a CVS update, remade & reinstalled ROOT, and now am
running ROOT 3.03/02...
and the problem described below still exists.
-----Original Message-----
From: Colley, Tony
Sent: Tuesday, February 26, 2002 15:37
To: 'ROOT Talk'
Subject: zoomed in TGraph bug
The following demonstrates a "minor" bug in TGraph:
{
Int_t i;
Float_t x[1000];
Float_t y[1000];
for (i=0; i<1000; i++)
{
x[i] = 0.001*i;
y[i] = 6.2831853*x[i];
y[i] = sin(12*y[i]) + sin(17*y[i]) + sin(56*y[i]) + sin(74*y[i]);
}
TGraph *graph = new TGraph( 1000, x, y );
graph->Draw("AL");
printf(
"\n\n===============================================================\n" );
printf( "Right click on X axis and select SetRangeUser.\n" );
printf( "Enter the range 0.387 to 0.389 and click OK.\n" );
printf( "Move the cursor over one of the 3 points (at .387, .388, .389).\n"
);
printf( "Press down the left mouse button.\n" );
printf( "When I do it, there are 6 extra boxes drawn\n" );
printf( " (in addition to the three that should be drawn)\n" );
printf( "===============================================================\n"
);
}
(I've attached the same thing as tgdemo.C, in case that's easier to use than
just cutting/pasting from this email)
The y function was chosen arbitrarily. The bug appears for many other
functions I tried.
The bug is even more insidious when you significantly increase the number of
data points graphed. When you zoom in close enough to begin seeing
individual points, in addition to having many extra boxes, some boxes are
apparently drawn too close to the edges because there is a wraparound effect
(giving rectangles spanning the graph rather than little boxes around the
points).
I also noticed in the example I provided, if you don't zoom in quite so far,
there are extra boxes drawn extending out of the left and right sides of the
graph. These boxes seem to correspond to data points outside the graph
clipping area but within the canvas clipping area. I'm not sure if I would
classify this behaviour as a bug or a feature... it could be useful and may
be intentional (i.e. a feature).
Tony Colley
ITT Industries A/CD
Fort Wayne, IN USA
Using ROOT 3.03/00, last updated from CVS on 18 Feb 2002, on RedHat Linux
7.2
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