here follows a little explenation on using custom graphics contexts
in the TG widgets. A graphics context (GContext_t) defines attributes
with which primitives are drawn. All widget classes define some static protected
GC's that are used when creating a corresponding widget object. Most widgets
share the same GC as to get a coherent looking interface while defining only
a few GC's (all default GC's are defined in the TGClient class).
To create a widget with, for example, a non default color one has to define
a new GC and pass that in the widget ctor. In the example below we create
a TGLabel with a red foreground color (plug this piece of code in the
$ROOTSYS/guitest.cxx just above "fLtitle = "). To see the red label
click on "Click here".
// Create new graphics context for drawing of TGlabel with text in red.
// Use default font as specified in .rootrc
FontStruct_t labelfont;
labelfont = gClient->GetFontByName(gEnv->GetValue("Gui.NormalFont",
"-adobe-helvetica-medium-r-*-*-12-*-*-*-*-*-iso8859-1"));
// Define new graphics context. Only the fields specified in
// fMask will be used (for default TGLabel context see
// http://root.cern.ch/root/html/src/TGClient.cxx.html).
GCValues_t gval;
gval.fMask = kGCForeground | kGCFont;
gval.fFont = gGXW->GetFontHandle(labelfont);
gClient->GetColorByName("red", gval.fForeground);
GContext_t redlabelgc = gGXW->CreateGC(gClient->GetRoot()->GetId(), &gval);
fLtitle = new TGLabel(f4, new TGString("Title:"), redlabelgc);
Once you have a custom GC you can copy or change it using gGXW->CopyGC() and
gGXW->ChangeGC(). Once all widgets using the custom GC's are deleted you
should also delete the GC using: gGXW->DeleteGC(redlabelgc);
Cheers, Fons.
Wei Xie wrote:
>
> Dear Rooters,
>
> One more question about TGLabel, please.
>
> A TGLabel has the following ctor:
>
> TGLabel(const TGWindow *p, TGString *text,
> GContext_t norm = fgDefaultGC,
> FontStruct_t font = fgDefaultFontStruct,
> UInt_t options = kChildFrame,
> ULong_t back = fgDefaultFrameBackground);
>
> Could you tell me how to get value of
> "fgDefaultGC" and "kChildFrame" ?
>
> Sincerely
>
> Xie
>
> W__W W__W
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-- Org: CERN, European Laboratory for Particle Physics. Mail: 1211 Geneve 23, Switzerland Phone: +41 22 7679248 E-Mail: Fons.Rademakers@cern.ch Fax: +41 22 7677910