[Mesa-dev] [RFC] New EGL extension: EGL_EXT_platform_display

[Chad Versace]

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

I'm seeking feedback on an EGL extension that I'm drafting. The ideas have
already been discussed at Khronos meetings to a good reception, but I want
feedback from Mesa developers too.

Summary
- -------
The extension, tentatively named EGL_EXT_platform_display, enables EGL clients
to specify to which platform (X11, Wayland, gbm, etc) an EGL resource
(EGLDisplay, EGLSurface, etc) belongs when the resource is derived from
a platform-native type. As a corollary, the extension enables the creation of
EGL resources from different platforms within a single process.


Feedback
- --------
I'd like to hear feeback about the details below. Do you see any potential
problems? Is it lacking a feature that you believe should be present?


Details
- -------
The draft extension defines the following new functions:

    // This is the extenion's key function.
    //
    EGLDisplay
    eglGetPlatformDisplayEXT(EGLenum platform, void *native_display);

    // The two eglCreate functions below differ from their core counterparts
    // only in their signature. The EGLNative types are replaced with void*.
    // This makes the signature agnostic to which platform the native resource
    // belongs.

    EGLSurface
    eglCreatePlatformWindowSurfaceEXT(EGLDisplay dpy,
                                      EGLConfig config,
                                      void *native_window,
                                      const EGLint *attrib_list);

    EGLSurface
    eglCreatePlatformPixmapSurface(EGLDisplay dpy,
                                   EGLConfig config,
                                   void *native_pixmap,
                                   const EGLint *attrib_list);

Valid values for `platform` are defined by layered extensions.  For
example, EGL_EXT_platform_x11 defines EGL_PLATFORM_X11, and
EGL_EXT_platform_wayland defines EGL_PLATFORM_WAYLAND.

Also, the layered extensions specify which native types should be passed as
the native parameters. For example, EGL_EXT_platform_wayland specifies that,
when calling eglCreatePlatformWindowSurfaceEXT with a display that was derived
from a Wayland display, then the native_window parameter must be `struct
wl_egl_window*`. Analogously, EGL_EXT_platform_x11 specifies that
native_window must be `Window*`.


Example Code for X11
- --------------------
// The internal representation of the egl_dpy, created below, remembers that
// it was derived from an Xlib display.

Display *xlib_dpy = XOpenDisplay(NULL);
EGLDisplay *egl_dpy = eglGetPlatformDisplayEXT(EGL_PLATFORM_X11, xlib_dpy);

EGLConfig config;
eglChooseConfig(egl_dpy, &config, ...);

// Since egl_dpy remembers that it was derived from an Xlib display, when
// creating the EGLSurface below libEGL internally casts the
// `(void*) &xlib_win` to `Window*`.

Window xlib_win = XCreateWindow(xlib_dpy, ...);
EGLSurface egl_surface = eglCreatePlatformWindowSurfaceEXT(egl_dpy, config,
                                                           (void*) &xlib_win,
                                                           NULL);

Example Code for Wayland
- ------------------------
// The internal representation of the egl_dpy, created below, remembers that
// it was derived from a Wayland display.

struct wl_display *wl_dpy = wl_display_connect(NULL);
EGLDisplay *egl_dpy = eglGetPlatformDisplay(EGL_PLATFORM_WAYLAND, wl_dpy);


EGLConfig config;
eglChooseConfig(egl_dpy, &config, ...);

// Since egl_dpy remembers that it was derived from an Wayland display, when
// creating the EGLSurface below libEGL internally casts the
// `(void*) wl_win` to `struct wl_egl_window*`.

struct wl_egl_window *wl_win = wl_egl_window_create(...);
EGLSurface egl_surface = eglCreateWindowSurface(egl_dpy, config,
                                               (void*) wl_win, NULL);
-----BEGIN PGP SIGNATURE-----
Version: GnuPG v2.0.19 (GNU/Linux)
Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/
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=MP7i
-----END PGP SIGNATURE-----