Add EGL xcb platform

This enables GL applications to be written without any involvement of
Xlib.

EGL X11 platform is actually already xcb-only underneath, so this commit
just add the necessary interface changes so eglDisplay can be created
from a xcb_connection_t.

Reviewed-by: Adam Jackson <ajax@redhat.com>
Signed-off-by: Yuxuan Shui <yshuiv7@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6474>

src/egl/main/eglapi.c

@@ -388,6 +388,11 @@ _eglGetPlatformDisplayCommon(EGLenum platform, void *native_display,
       disp = _eglGetX11Display((Display*) native_display, attrib_list);
       break;
 #endif
+#ifdef HAVE_XCB_PLATFORM
+   case EGL_PLATFORM_XCB_EXT:
+      disp = _eglGetXcbDisplay((xcb_connection_t*) native_display, attrib_list);
+      break;
+#endif
 #ifdef HAVE_DRM_PLATFORM
    case EGL_PLATFORM_GBM_MESA:
       disp = _eglGetGbmDisplay((struct gbm_device*) native_display,

src/egl/main/egldisplay.c

@@ -70,6 +70,7 @@ static const struct {
    const char *name;
 } egl_platforms[] = {
    { _EGL_PLATFORM_X11, "x11" },
+   { _EGL_PLATFORM_XCB, "xcb" },
    { _EGL_PLATFORM_WAYLAND, "wayland" },
    { _EGL_PLATFORM_DRM, "drm" },
    { _EGL_PLATFORM_ANDROID, "android" },
@@ -506,6 +507,27 @@ _eglGetX11Display(Display *native_display,
 }
 #endif /* HAVE_X11_PLATFORM */
 
+#ifdef HAVE_XCB_PLATFORM
+_EGLDisplay*
+_eglGetXcbDisplay(xcb_connection_t *native_display,
+                  const EGLAttrib *attrib_list)
+{
+   /* EGL_EXT_platform_xcb recognizes exactly one attribute,
+    * EGL_PLATFORM_XCB_SCREEN_EXT, which is optional.
+    */
+   if (attrib_list != NULL) {
+      for (int i = 0; attrib_list[i] != EGL_NONE; i += 2) {
+         if (attrib_list[i] != EGL_PLATFORM_XCB_SCREEN_EXT) {
+            _eglError(EGL_BAD_ATTRIBUTE, "eglGetPlatformDisplay");
+            return NULL;
+         }
+      }
+   }
+
+   return _eglFindDisplay(_EGL_PLATFORM_XCB, native_display, attrib_list);
+}
+#endif /* HAVE_XCB_PLATFORM */
+
 #ifdef HAVE_DRM_PLATFORM
 _EGLDisplay*
 _eglGetGbmDisplay(struct gbm_device *native_display,

src/egl/main/egldisplay.h

@@ -45,6 +45,7 @@ extern "C" {
 
 enum _egl_platform_type {
    _EGL_PLATFORM_X11,
+   _EGL_PLATFORM_XCB,
    _EGL_PLATFORM_WAYLAND,
    _EGL_PLATFORM_DRM,
    _EGL_PLATFORM_ANDROID,
@@ -294,6 +295,12 @@ _EGLDisplay*
 _eglGetX11Display(Display *native_display, const EGLAttrib *attrib_list);
 #endif
 
+#ifdef HAVE_XCB_PLATFORM
+typedef struct xcb_connection_t xcb_connection_t;
+_EGLDisplay*
+_eglGetXcbDisplay(xcb_connection_t *native_display, const EGLAttrib *attrib_list);
+#endif
+
 #ifdef HAVE_DRM_PLATFORM
 struct gbm_device;
 

src/egl/main/eglglobals.c

@@ -89,6 +89,9 @@ struct _egl_global _eglGlobal =
    " EGL_EXT_platform_x11"
    " EGL_KHR_platform_x11"
 #endif
+#ifdef HAVE_XCB_PLATFORM
+   " EGL_MESA_platform_xcb"
+#endif
 #ifdef HAVE_DRM_PLATFORM
    " EGL_MESA_platform_gbm"
    " EGL_KHR_platform_gbm"