Re: A simple question on XCBGCFunction (when value[0] = XCBGXxor)

Oh, and the other thing you need is an XCBFlush(c) after your drawing  
commands.

Ian

On May 18, 2006, at 8:02 AM, Ian Osgood wrote:

> Hi, Osmo!
>
> I was not able to get this to work unless I used  
> XCBLineStyleDoubleDash.  Then xor did the right thing.  You can  
> also verify this behavior using the "xgc" app.
>
> Dashed lines have very complex behavior, which seems to be affected  
> by many GC params, including Function, Foreground, Background,  
> LineStyle, LineWidth, DashOffset, DashList, and Stipple.  I'm not  
> sure what the best combination is for this kind of interactive  
> bounding box.
>
> (BTW, you want to use XCBCoordModeOrigin below.)
>
> Ian
>
> On May 18, 2006, at 2:04 AM, Osmo Maatta wrote:
>
> > Hello,
> >
> > I try to create a GC (graphic context) to draw some rubber lines  
> > using the XOR pen.
> >
> > I do this:
> >
> >  XCBGCONTEXT    sel_rect;
> >  ....
> >
> >  sel_rect = XCBGCONTEXTNew (c);
> >  mask =   XCBGCFunction | XCBGCForeground | XCBGCLineStyle |  
> > XCBGCGraphicsExposures;
> >  values[0] = XCBGXxor;  values[1] = screen->black_pixel;
> >  values[2] = XCBLineStyleOnOffDash;
> >  values[3] = 0;
> >  XCBCreateGC (c, sel_rect,  win, mask, values);
> >
> >
> > and later in
> >
> > case XCBExpose:
> > {
> >     printf("Debug expose\n");
> >
> >     XCBPolyRectangle (c, win, sel_rect, 2, rectangles);
> >           XCBPolyLine (c, CoordModeOrigin, win, sel_rect, 4,  
> > polyline);
> >
> >     break;
> > }
> > ---------------------------------
> >   But it does not draw anything. Only the debug line appears on  
> > the console.
> > -------------------
> >
> > I have even tried with  XCBGXcopy  value as XCBGCFunction.
> >
> > values[0] = XCBGXcopy;
> > Xlib manual says that GXcopy is the default GCFunction. I suppose  
> > it's the same in XCB.
> > But it does not work.
> >
> > It works (draws lines in a window) if I remove XCBGCFunction from  
> > the mask and remove the value[0]= line.
> > How to use the values for XCBGCFunction mask ?
> > -------------------------------------------------------------------
> >
> > I follow this tutorial
> > http://www.iecn.u-nancy.fr/~torri/files/xcb/doc/
> >
> > Many TIA.
> >  Osmo
> >
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