DRI interface changes

[<kr...@bi...>]

Hi,

I've been working on updating the DRI interface
(GL/internal/dri_interface.h) the last few days and I though I'd post
a heads up to the lists to get some feedback.  The work I've been
doing starts out with the patches in bug 5714, implements Ians
suggestions in comment #20, and quite a bit more.  I haven't added
Alans frontbuffer mapping patches yet; I wanted to get this work done
first before breaking DDX compatibility, but they're next.

The work is on the dri2 branch in git.freedesktop.org/~krh/mesa.git or
browsable here:

http://people.freedesktop.org/krh-cgi/cgit?r=_home_krh_mesa.git&p=log&h=dri2

The changes are mostly a series of cleanup as described below, but
there is a new concept in there: the DRI extension.  Much of the churn
in the DRI interface structs is from adding and removing functions
pertaining to GLX extensions, most recently GLX_MESA_copy_sub_buffer
and probably soon GLX_EXT_texture_from_pixmap.  The DRI extension
mechanism should allow us to add and remove support for extensions as
they come and go, in a way that doesn't break ABI or API.

The idea here is that only the core GLX 1.4 features should be part of
the __DRI{screen,context,drawable} structs and everything else must be
exposed as a __DRIextension.  The list of __DRIextensions is available
using __DRIscreen::getExtensions;

    const __DRIextension **(*getExtensions)(__DRIscreen *screen);

All extensions have a common "baseclass" that just is the name of the
extension  (just a string):

    struct __DRIextensionRec {
        const char *name;
    };

If the name matches that of an extension known to the loader, the
loader can cast the struct to a more specific extension struct that
has the function pointers that provide access to the functionality.
For example:

    #define __DRI_COPY_SUB_BUFFER "DRI_CopySubBuffer"
    struct __DRIcopySubBufferExtensionRec {
        __DRIextension base;
        void (*copySubBuffer)(__DRIdrawable *drawable,
                              int x, int y, int w, int h);
    };

The presence of an extension means that the driver can provide some
extra functionality.  Based of these extra hooks, the loader will be
able to implement and advertise a number of GLX extensions.  The DRI
extension name space is private to the DRI interface, and is
orthogonal to the GLX extension name space.  The logic here is that
one DRI extension can enable a number of GLX extensions, and the
loader, since it has to implement the entry points, will know exactly
which GLX extensions to enable.  For example, the DRI_SwapControl
extension:

#define __DRI_SWAP_CONTROL "DRI_SwapControl"
struct __DRIswapControlExtensionRec {
    __DRIextension base;
    void (*setSwapInterval)(__DRIdrawable *drawable, unsigned int inteval);
    unsigned int (*getSwapInterval)(__DRIdrawable *drawable);
};

enables the loader to implement both GLX_SGI_swap_control and
GLX_MESA_swap_control.

Aside from the new extension mechanism, the branch cleans up a number
of things in the DRI interface:

1) Move XIDs out of the interface and make libGL handle XID ->
__DRIdrawable etc mapping.  I've pulled the hashtable from libdrm into
mesa to do this, which should allow us to drop the hashtable and the
skip list from drm eventually.

2) Drop the display notion from the interface.  A DRI driver only
handles one screen and

3) Remove getProcAddress (only needed by the old extension mechanism),
create/destroyContext, create/destroyDrawable (instead of calling back
from the DRI driver, just have the loader create the context first and
pass the drm_context_t into the driver).

4) Remove variables from the __DRI* structs except the private
pointer.  We should never share state across the DRI driver boundary,
all access should go through functions.

5) Misc cleanups: pull the createNewScreen out of the driver backends
and into dri/common (more code sharing, simpler interface between
dri/common and drivers), always use the __DRI* types instead of
private void pointers (type safety, interface is more
self-documenting), generate entry point name using macros instead of
duplication the version number in a few places, drop now unused
__DRIid typedef.

cheers,
Kristian