Re: Get & Set pixel from a pixmap.

[Ian Britten <britten caris com>]

On Tue, 05 Mar 2002 09:07:20 -0500
Paul Davis <pbd Op Net> wrote:

> >I want to get & then set a pixel value from a GdkPixmap, but can't seem to
> >find where to start.  I see that pixels can be manipulated in a GdkImage
> >using gdk_image_get_pixel() & gdk_image_put_pixel(), however I need to
> >manipulate an off-screen pixmap rather than a copy of the window.
> 
> you can't manipulate a GdkPixmap this way. its a server side resource,
> and doesn't exist in the memory space of the client (modulo the MIT
> SHM extension for X). the only way to manipulate it are through the
> existing functions calls, and they do not (AFAIK) include any
> pixel-level manipulation (though if you were insistent on this
> approach, you could probably paint a single pixel line over and over :)
> 
> a GdkImage is a client side resource, and hence can be accessed on a
> pixel-by-pixel basis. however, it has to be drawn en-masse to a window
> in order to see it (same as a GdkPixmap, but requiring more data
> transfer between the client and server.

Ya, that's what we're looking to do...  (Pull an image from a background
pixmap (or, a subset of it), manipulate a bunch of the pixels, then put
the image back onto the screen)

We actually found the problem, and it appears to be solved in v2...
In v1.2, the function gdk_image_get() takes in a GdkWindow.  (Ack!)
In v2, gdk_image_get() seems to have been fixed to only require a
GdkDrawable (which is what we have...)
[ This is consistent with the underlying XGetImage(), which only needs a
Drawable... ]

(sigh)  Now all we have to do is try to upgrade to v2 (earlier than I had
planned)... :-/  Hopefully it's straightforward, but the Windows version
has me a little worried...
Thanks all!
Ian