[Xcb] To do

[Vincent Torri]

On Sun, 6 Feb 2005, Jamey Sharp wrote:

> On Sat, Feb 05, 2005 at 06:29:37PM +0100, Vincent Torri wrote:
> > > Ooh, that's cool. If you've implemented everything that XImage supports,
> > > then you've figured out possibly the most confusing part of the core X
> > > protocol. Congratulations! You'll have to explain it to me sometime. :-)
> >
> > I've not implemented all the functions. I've only create a similar
> > structure, and implemented:
> >
> > xcb_image_create
> > xcb_image_init
> > xcb_image_destroy
> > xcb_image_get
> > xcb_image_put
> > xcb_image_put_pixel
> > xcb_image_get_pixel
> >
> > for now, only xcb_image_put does not work (from one test). I don't
> > understand why. Is there a known reason why XCBPutImage would do nothing ?
>
> Are you checking for X errors in response to your PutImage? It's hard,
> in my opinion, to get the parameters right, and the X server will at
> least tell you if you get them wrong.

nope, for only one reason: there's no doc about how handling errors with
xcb, and it's something that i want to add to my tuto (how to interpret
the errors)

>
> The only time I've successfully coded a call to XCBPutImage was when I
> carefully copied code from XImage and then Keith Packard fixed my bugs.
> (So I guess you could say I've never successfully used PutImage.) That
> code is in
> 	http://cvs.cairographics.org/cairo/src/cairo_xcb_surface.c?rev=HEAD&view=auto
> in the _cairo_xcb_surface_set_image function.
>
> The only other correct use of XCBPutImage that I'm aware of is in David
> Reveman's rendertest program, in
> 	http://cvs.cairographics.org/rendertest/src/xcb.c?rev=HEAD&view=auto
> in the _xcb_render_set_pixels function. (That program turned out to be
> the first test case for XCB's support for the BIG-REQUESTS extension,
> for whatever that's worth.)
>

thank you, i'll look at them.

> > What should i use for the graphic context to pass to it ?
>
> You could create a new GC and use it once for your PutImage request,
> like David's code does. There are some GC parameters that I imagine do
> interesting things to PutImage requests, but that interaction is poorly
> documented, as far as I can tell.
>

that's also what i thought.

> > > Unfortunately, if your code does everything XImage does, that means that
> > > it's more complicated than the piece I want to put in XCB, which I think
> > > shouldn't do any format conversion -- just image splitting for core X,
> > > and SHM where possible. Fortunately, I think that's probably easy
> > > functionality to separate, so we can put the little stuff in libXCB and
> > > make the rest available as a separate library or something.
> > >
> > > I look forward to seeing your code, anyway.
> >
> > Well, it's almost all the code from Xorg (all the difficult part). I don't
> > think it's very interesting. And even if i understand lots of the code,
> > some parts are mysterious for me :)
>
> One of the high-priority tasks on the XCB to-do list for a long time has
> been to "Understand and document X image formats, as per GetImage and
> PutImage..." That's because when I was trying to write the original XCL,
> I discovered that both the code and the documentation are mostly
> incomprehensible in this area.
>
> I've just Googled for image format documentation again, but still can't
> find anything very useful.

hehe, i've searched several days with google before writing the XCBImage
stuff. And i've never found an explicit explanation of the Zpixmap and
XYPixmap.
Now, I know how Zpixmap works. But for XYPixmap, it's more difficult to
understand, as i have no doc... (and in France, i can't get O'Reilly
books, which should explain that)

Vincent