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["Jorge Gaete" <jgaete informat cl>]

----- Original Message -----
From: Sven LUTHER <luther@dpt-info.u-strasbg.fr>
To: <gtk-list@redhat.com>
Cc: Sven LUTHER <luther@dpt-info.u-strasbg.fr>
Sent: Monday, November 08, 1999 9:10 AM
Subject: [gtk-list] colormap on TRUECOLOR visual.


> Hello, ...
>
> i did a small graphical toolkit using gtk+, and wrapping the gdk_draw
stuff.
>
> I had a function that get the color associated with a pixel of an image.
>
> i do a :
>
> cmap = gdk_colormap_get_system ();
>
> and later, i allocate a color to the colormap with :
>
> GdkColor *col;
> col = malloc(GdkColor);
> col->red=65535;
> col->green=col->blue=0;
> gdk_colormap_alloc_color (cmap, col, FALSE, TRUE)
> gdk_gc_set_foreground (gc, col);
>
>
> and draw with it onto a pixmap with :
>
> gdk_draw_point (pixmap, gc, x, y);
>
> When i want to get the color of a given pixel of the pixmap, i do the
> following :
>
> GdkColor *getted_col;
> img = gdk_image_get (pixmap, 0, 0, x+1, y+1);
> pixel = gdk_image_get_pixel (img, x, y);
> getted_col = cmap->colors[pixel];
>
> This worked fine on my sun ultra1 under solaris, who had pseudo color
visuals,
> but now that i have a linux box with a G400, i have truecolor visuals (at
> least that is what fbset tells me) and the colors field of the colormap is
> null, and thus i get a nice segfault when accesing  cmap->colors[pixel].
>
> This is very disturbing.
>
> I understand that in a truecolor visual, the color is written directly to
the
> pixmap, and thus i think that the pixel returned is directly the color
wanted,
> or something similar (a white pixel gives me 16777215 and a red one gives
me
> 16711680).
>
> Did i understand things correctly, and is this normal behavior (since
> truecolor visual don't have colormaps) and in this case should there not
be
> some kind of function for getting the color associated with a given pixel
?
> something like :
>
> GdkColor *gdk_colormap_get_color (GdkColormap *colormap, guint pixel);
>
> Or am i supposed to check in which kind of visual i am and handle this
stuff
> myself ? I don't think this would be correct to do.
>
> or maybe did i understand all wrong what is going on here ? In which case,
> what is the correct way of doing things ?
>
> Friendly,
>
> Sven LUTHER
>
> --
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