[Mesa-dev] [PATCH] egl: Introduce alternative native display types

[Kristian Høgsberg]

The EGL native platform API is determined at compile time and resolves
to Win32, X11 or Symbian at this point.   This means that if we want to
support XCB or a native DRM implementation, they have to be their platforms
and result in different libEGL.so's with identical ABI but different
entrypoint semantics.  From a distro point of view, and really, any point
of view, this is a mess, since the different libraries can't easily co-exist
without fiddling with linker paths.  And if you get it wrong, an application
requiring the X11 platform libEGL.so will happily link against any other
libEGL.so and segfault when eglGetDisplay() doesn't do what it expects.

We can get around this by overloading the X11 native entrypoints instead.
The X Display struct has as its first member a pointer to XExtData.  The
pointer will always have bits 0 and 1 set to 0, which we can use to
distinguish a struct that's not an X display.  This lets us pass in a
custom struct that can provide initialization data for other platforms
in the same libEGL.so.

The convention we're establishing is that the first field of such a struct
must be a pointer, so as to overlap with the layout of the X display
struct.  We can then enummerate the different display types using odd
numbers cast to a pointer (ensuring bit 0 is set).  This patch introduces
two new types of displays: EGL_DISPLAY_TYPE_DRM_MESA which lets us
initialize EGL directly on a DRM file descriptor or device filename and
EGL_DISPLAY_TYPE_XCB_MESA which lets us initialize EGL on X using an
xcb_connection_t instead of a classic Xlib Display.
---
 include/EGL/eglplatform.h       |   17 ++++++++++++++
 src/egl/drivers/dri2/egl_dri2.c |   45 ++++++++++++++++++++++++++++++--------
 2 files changed, 52 insertions(+), 10 deletions(-)

diff --git a/include/EGL/eglplatform.h b/include/EGL/eglplatform.h
index c625088..f9d0eb3 100644
--- a/include/EGL/eglplatform.h
+++ b/include/EGL/eglplatform.h
@@ -88,6 +88,23 @@ typedef Display *EGLNativeDisplayType;
 typedef Pixmap   EGLNativePixmapType;
 typedef Window   EGLNativeWindowType;
 
+typedef struct EGLDisplayTypeMESA EGLDisplayTypeMESA;
+
+#define EGL_DISPLAY_TYPE_DRM_MESA ((EGLDisplayTypeMESA *) 1)
+
+typedef struct EGLDisplayTypeDRMMESA {
+   const EGLDisplayTypeMESA *type;
+   const char *device;
+   int fd;
+} EGLDisplayTypeDRMMESA;
+
+#define EGL_DISPLAY_TYPE_XCB_MESA ((EGLDisplayTypeMESA *) 3)
+
+typedef struct EGLDisplayTypeXCBMESA {
+   const EGLDisplayTypeMESA *type;
+   struct xcb_connection_t *conn;
+} EGLDisplayTypeXCBMESA;
+
 #else
 #error "Platform not recognized"
 #endif
diff --git a/src/egl/drivers/dri2/egl_dri2.c b/src/egl/drivers/dri2/egl_dri2.c
index a7030f0..39c90b3 100644
--- a/src/egl/drivers/dri2/egl_dri2.c
+++ b/src/egl/drivers/dri2/egl_dri2.c
@@ -634,6 +634,10 @@ dri2_add_configs_for_visuals(struct dri2_egl_display *dri2_dpy,
    return EGL_TRUE;
 }
 
+struct generic_display {
+   void *pointer;
+};
+
 /**
  * Called via eglInitialize(), GLX_drv->API.Initialize().
  */
@@ -645,25 +649,42 @@ dri2_initialize(_EGLDriver *drv, _EGLDisplay *disp,
    struct dri2_egl_display *dri2_dpy;
    char path[PATH_MAX], *search_paths, *p, *next, *end;
    unsigned int api_mask;
+   struct generic_display *generic;
+   EGLDisplayTypeDRMMESA *drm_display;
+   EGLDisplayTypeXCBMESA *xcb_display;
 
    dri2_dpy = malloc(sizeof *dri2_dpy);
    if (!dri2_dpy)
       return _eglError(EGL_BAD_ALLOC, "eglInitialize");
 
+   memset(dri2_dpy, 0, sizeof *dri2_dpy);
    disp->DriverData = (void *) dri2_dpy;
+   generic = (struct generic_display *) disp->NativeDisplay;
+
    if (disp->NativeDisplay == NULL) {
       dri2_dpy->conn = xcb_connect(0, 0);
       if (!dri2_dpy->conn) {
 	 _eglLog(_EGL_WARNING, "DRI2: xcb_connect failed");
 	 goto cleanup_dpy;
       }
-   } else {
+   } else if (generic->pointer == EGL_DISPLAY_TYPE_DRM_MESA) {
+      drm_display = (EGLDisplayTypeDRMMESA *) disp->NativeDisplay;
+      if (drm_display->device) {
+	 dri2_dpy->device_name = strdup(drm_display->device);
+      } else {
+	 dri2_dpy->fd = drm_display->fd;
+      }
+      dri2_dpy->driver_name = strdup("i965");
+   } else if (generic->pointer == EGL_DISPLAY_TYPE_XCB_MESA) {
+      xcb_display = (EGLDisplayTypeXCBMESA *) disp->NativeDisplay;
+      dri2_dpy->conn = xcb_display->conn;
+   } else if (((long) generic->pointer & 1) == 0) {
       dri2_dpy->conn = XGetXCBConnection(disp->NativeDisplay);
+   } else {
+      _eglLog(_EGL_WARNING,
+	      "DRI2: unknown display type: %d", (long) generic->pointer);
    }
 
-   if (dri2_dpy->conn == NULL)
-      goto cleanup_conn;
-
    if (dri2_dpy->conn) {
       if (!dri2_connect(dri2_dpy))
 	 goto cleanup_conn;
@@ -709,12 +730,13 @@ dri2_initialize(_EGLDriver *drv, _EGLDisplay *disp,
    if (!dri2_bind_extensions(dri2_dpy, dri2_driver_extensions, extensions))
       goto cleanup_driver;
 
-   dri2_dpy->fd = open(dri2_dpy->device_name, O_RDWR);
-   if (dri2_dpy->fd == -1) {
-      _eglLog(_EGL_WARNING,
-	      "DRI2: could not open %s (%s)", dri2_dpy->device_name,
-              strerror(errno));
-      goto cleanup_driver;
+   if (dri2_dpy->device_name != NULL) {
+      dri2_dpy->fd = open(dri2_dpy->device_name, O_RDWR);
+      if (dri2_dpy->fd == -1) {
+	 _eglLog(_EGL_WARNING, "DRI2: could not open %s (%s)",
+		 dri2_dpy->device_name, strerror(errno));
+	 goto cleanup_driver;
+      }
    }
 
    if (dri2_dpy->conn) {
@@ -787,6 +809,9 @@ dri2_initialize(_EGLDriver *drv, _EGLDisplay *disp,
    *major = 1;
    *minor = 4;
 
+   if (generic->pointer == EGL_DISPLAY_TYPE_DRM_MESA)
+      drm_display->fd = dri2_dpy->fd;
+
    return EGL_TRUE;
 
  cleanup_configs:
-- 
1.7.0.1