How to draw transparent ellipses

ROOT
1

Hi, I am trying to draw several unfilled ellipses (ie transparent so you can see all the ellipses although they are partially overlapping). Currently I can draw the ellipses great, but they are not transparent.

I tried to use these directions: root.cern.ch/root/html/TColor.html#C06

But when I run this I get the error: Error: Can’t call TColor::SetAlpha(0.01) in current scope

I googled this error and some documentation at Duke say the GUI backend must be set to qt in order to use this feature (www.phy.duke.edu/~dmb60/the-guide/). But I am running on lxplus5 at CERN, so I don’t see a ~/.rootrc file to edit with these lines to set the qt background.

Is it possible to use this transparency feature?

2

This feature has been introduced very recently.
You need to have the latest ROOT 5.34 or the ROOT 6 which will be released next week.

Not all graphics backend support transparency. You will see it on the screen if you run with OpenGL (on all platforms) or Cocoa (on Mac only). On the file output you will see it in with PDF, PNG, Gif, JPeg … but not PS.

Note that if you need fully transparent ellipses you can always draw then as lines.