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>

docs/relnotes/new_features.txt

@@ -0,0 +1 @@
+EGL_MESA_platform_xcb

include/EGL/eglext.h

@@ -883,6 +883,12 @@ EGLAPI EGLSurface EGLAPIENTRY eglCreatePlatformPixmapSurfaceEXT (EGLDisplay dpy,
 #define EGL_PLATFORM_X11_SCREEN_EXT       0x31D6
 #endif /* EGL_EXT_platform_x11 */
 
+#ifndef EGL_MESA_platform_xcb
+#define EGL_MESA_platform_xcb 1
+#define EGL_PLATFORM_XCB_EXT              0x31DC
+#define EGL_PLATFORM_XCB_SCREEN_EXT       0x31DE
+#endif /* EGL_MESA_platform_xcb */
+
 #ifndef EGL_EXT_protected_content
 #define EGL_EXT_protected_content 1
 #define EGL_PROTECTED_CONTENT_EXT         0x32C0

meson.build

@@ -827,6 +827,7 @@ gl_pkgconfig_c_flags = []
 if with_platform_x11
   if with_any_vk or with_egl or (with_glx == 'dri' and with_dri_platform == 'drm')
     pre_args += '-DHAVE_X11_PLATFORM'
+    pre_args += '-DHAVE_XCB_PLATFORM'
   endif
   if with_glx == 'xlib' or with_glx == 'gallium-xlib'
     pre_args += '-DUSE_XSHM'

src/egl/drivers/dri2/egl_dri2.c

@@ -183,6 +183,11 @@ dri_is_thread_safe(void *loaderPrivate)
       return false;
 #endif
 
+#ifdef HAVE_XCB_PLATFORM
+   if (display->Platform == _EGL_PLATFORM_XCB)
+      return true;
+#endif
+
 #ifdef HAVE_WAYLAND_PLATFORM
    if (display->Platform == _EGL_PLATFORM_WAYLAND)
       return true;
@@ -1178,6 +1183,7 @@ dri2_initialize(_EGLDisplay *disp)
       ret = dri2_initialize_device(disp);
       break;
    case _EGL_PLATFORM_X11:
+   case _EGL_PLATFORM_XCB:
       ret = dri2_initialize_x11(disp);
       break;
    case _EGL_PLATFORM_DRM:

src/egl/drivers/dri2/platform_x11.c

@@ -1212,7 +1212,8 @@ dri2_find_screen_for_display(const _EGLDisplay *disp, int fallback_screen)
    const EGLAttrib *attr;
 
    for (attr = disp->Options.Attribs; attr; attr += 2) {
-      if (attr[0] == EGL_PLATFORM_X11_SCREEN_EXT)
+      if (attr[0] == EGL_PLATFORM_X11_SCREEN_EXT ||
+          attr[0] == EGL_PLATFORM_XCB_SCREEN_EXT)
          return attr[1];
    }
 
@@ -1232,10 +1233,14 @@ dri2_get_xcb_connection(_EGLDisplay *disp,
       dri2_dpy->conn = xcb_connect(NULL, &screen);
       dri2_dpy->own_device = true;
       screen = dri2_find_screen_for_display(disp, screen);
-   } else {
+   } else if (disp->Platform == _EGL_PLATFORM_X11) {
       Display *dpy = disp->PlatformDisplay;
       dri2_dpy->conn = XGetXCBConnection(dpy);
       screen = DefaultScreen(dpy);
+   } else {
+      /*   _EGL_PLATFORM_XCB   */
+      dri2_dpy->conn = disp->PlatformDisplay;
+      screen = dri2_find_screen_for_display(disp, 0);
    }
 
    if (!dri2_dpy->conn || xcb_connection_has_error(dri2_dpy->conn)) {

src/egl/generate/egl.xml

@@ -590,9 +590,10 @@
         <enum value="0x31D7" name="EGL_PLATFORM_GBM_MESA" alias="EGL_PLATFORM_GBM_KHR"/>
         <enum value="0x31D8" name="EGL_PLATFORM_WAYLAND_KHR"/>
         <enum value="0x31D8" name="EGL_PLATFORM_WAYLAND_EXT" alias="EGL_PLATFORM_WAYLAND_KHR"/>
-            <unused start="0x31DC" end="0x31DC"/>
+        <enum value="0x31DC" name="EGL_PLATFORM_XCB_EXT"/>
         <enum value="0x31DD" name="EGL_PLATFORM_SURFACELESS_MESA"/>
-            <unused start="0x31DE" end="0x31DF"/>
+        <enum value="0x31DE" name="EGL_PLATFORM_XCB_SCREEN_EXT"/>
+            <unused start="0x31DF" end="0x31DF"/>
     </enums>
 
     <!-- Due to an oversight in development, these enums alias the above MESA
@@ -2546,6 +2547,12 @@
                 <enum name="EGL_PLATFORM_X11_SCREEN_EXT"/>
             </require>
         </extension>
+        <extension name="EGL_EXT_platform_xcb" supported="egl">
+            <require>
+                <enum name="EGL_PLATFORM_XCB_EXT"/>
+                <enum name="EGL_PLATFORM_XCB_SCREEN_EXT"/>
+            </require>
+        </extension>
         <extension name="EGL_EXT_protected_content" supported="egl">
             <require>
                 <enum name="EGL_PROTECTED_CONTENT_EXT"/>

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"