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

[Patrick Sung <phsung ualberta ca>]

Owen Taylor wrote:

> 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().
The library is written for a video capture card, and they primarily 
provide Windows API but they have ported some  (important but low level) 
part of the library to Linux, and this is the only way I can get the 
image without screwing up the screen (the direct video memory write). 
It looks peculiar to me either, I will try to look into the buffer 
using GDB and if there is no clue at all I will try a test buffer.

> > 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,
Patrick