Re: Colours...

[Peter Zelezny <pzel dodo com au>]

On Mon, 3 Jun 2002 00:52:47 +0100
Ian Molton <spyro armlinux org> wrote:

> 2) Can someone explain the horrible mess that seems to obscure choosing
> a simple colour?
>
> I want to modify the (gtk2) scribble example so that I can draw a chart
> on the backing pixmap. to do this, I thought I would create my own GC
> with its own foreground colour, and simply draw a line.
>
> well, I thought I'd start simple and simply change the colour of the
> 'foreground' (the rectangle used to clear the pixmap). here is my
> attempt, which does not work:
>
> ----------------------------------------------------------------
> static GdkPixmap *pixmap = NULL;
>
> /* Create a new backing pixmap of the appropriate size */
> static gint configure_event( GtkWidget         *widget,
>                              GdkEventConfigure *event )
> {
>   GdkGC *backgroundgc;
>         GdkColor colour;
>         GdkVisual *visual;
>         GdkColormap *colourmap;
>
>   if (pixmap)
>     g_object_unref (pixmap);
>
>   pixmap = gdk_pixmap_new (widget->window,
>                            widget->allocation.width,
>                            widget->allocation.height,
>                            -1);
>
>         backgroundgc = gdk_gc_new(pixmap);
>         gdk_color_parse("004400", &colour);
>         visual = gdk_visual_get_system();
>         colourmap = gdk_colormap_new(visual, TRUE);
>         gdk_colormap_alloc_color(colourmap, &colour, FALSE, TRUE);
>         gdk_gc_set_foreground(backgroundgc, &colour);
>
>
>   gdk_draw_rectangle (pixmap,
>                       /*widget->style->white_gc,*/
>                         backgroundgc,
>                       TRUE,
>                       0, 0,
>                       widget->allocation.width,
>                       widget->allocation.height);
>
>   return TRUE;
> }

You probably need to copy your pixmap onto the screen (i.e. widget->window).
Otherwise all your drawing is in memory only.

I think you can also use the colormap of your widget when allocating
the color, rather than creating a new one.

colormap = gtk_widget_get_colormap (widget);
gdk_colormap_alloc_color (colormap, &colour, TRUE, TRUE);

-- 
Peter Zelezny.