Re: problem with drawing 32bit image to 16bit screen (works with 32/24 bit screen)

[Owen Taylor <otaylor redhat com>]

Patrick Sung <phsung ualberta ca> writes:

> Havoc Pennington wrote:
>
> > Patrick Sung <phsung ualberta ca> writes:
> >
> > > I was trying to draw a 32bit color image to both a 24bit system and
> > > 16 bit systems.  I got the 24bit system works but not the 16 bit
> > > systems. It seems that gdk isn't reading my 32bit color image
> > > properly because I got an image displayed twice adjacent to each
> > > other (on the 16bit system).
> >
> > Can you send us a small test case? This should certainly work.
> I can do it, but for now I can give you more information.
>
> The data comes from an XImage object (which some library is
> providing). I read off the XImage.data to get to the real data.  I
> also read the other fields in the XImage struct.  The following is the
> printf of those fields:
>
> width:[640] height:[482]
> depth:[24] bytes per line:[2560], bits_per_pixel:[32]
> image format:[2] (That's XYPixmap, but I don't think it makes any
> difference, unless it say it is a bitmap)
> bitmap_unit:[32]
> bitmap_pad:[32]
>
> Both the system give me the same XImage data.

I'm a little confused here. An XImage is typically a way of 
representing data as stored on the screen. It sounds like this
library is reusing XImage in a rather peculiar way to store
it's own data. It's a little hard to say what exactly it is
putting in there and whether that corresponds to what
gdk_draw_rgb_32_image().

> btw, the screen output of the 16bit system has different color (they
> are not entirely black and white (yes, I am taking b/w image using
> 32bit of color ;) )
>
> The call I used to draw the RGB image is:
>
>       gdk_draw_rgb_32_image (draw_area->window,
>                  draw_area->style->bg_gc[GTK_STATE_NORMAL],
>                  0,0,640,482,
>                  GDK_RGB_DITHER_NONE,
>                  buffer,
>                  640*4);
>
> draw_area is the gtk_drawing_area.
>
> Is that the *right way* to provide the GDKDrawable and GC to the function?
 
They shouldn't matter much. This call looks reasonable, but I'm
guessing the buffer has data in a different format than what
gdk_draw_rgb_32_image() expects. What I'd try doing is writing
some code to make simple example image (say black and white stripes)
and trying drawing that with gdk_draw_rgb_32_image() and see
if that works.

Regards,
                                        Owen