X11:: Add native access to X11 visual and XCB connection

Exposed via glfwGetX11Visual and glfwGetXCBConnection, these are useful when doing custom Vulkan surface creation.

README.md

@@ -121,6 +121,8 @@ information on what to include when reporting a bug.
 
 ## Changelog
 
+ - Added `glfwGetX11Visual` and `glfwGetXCBConnection`
+   native functions for accessing X11 visual and XCB connection handle
  - Added `GLFW_PLATFORM` init hint for runtime platform selection (#1958)
  - Added `GLFW_ANY_PLATFORM`, `GLFW_PLATFORM_WIN32`, `GLFW_PLATFORM_COCOA`,
    `GLFW_PLATFORM_WAYLAND`, `GLFW_PLATFORM_X11` and `GLFW_PLATFORM_NULL` symbols to

docs/news.dox

@@ -9,6 +9,13 @@
 
 @subsection features_34 New features in version 3.4
 
+@subsection native_x11_visual_and_xcb_connection_34 X11 native Visual and XCB connection access
+
+GLFW now supports X11 platform specific native functions for accessing
+the X11 visual and XCB connection handle:
+@ref glfwGetX11Visual and @ref glfwGetXCBConnection.
+
+
 @subsubsection runtime_platform_34 Runtime platform selection
 
 GLFW now supports being compiled for multiple backends and selecting between

include/GLFW/glfw3native.h

@@ -117,6 +117,7 @@ extern "C" {
  #if defined(GLFW_EXPOSE_NATIVE_X11) || defined(GLFW_EXPOSE_NATIVE_GLX)
   #include <X11/Xlib.h>
   #include <X11/extensions/Xrandr.h>
+  typedef struct xcb_connection_t xcb_connection_t;
  #endif
 
  #if defined(GLFW_EXPOSE_NATIVE_WAYLAND)
@@ -416,6 +417,38 @@ GLFWAPI void glfwSetX11SelectionString(const char* string);
  *  @ingroup native
  */
 GLFWAPI const char* glfwGetX11SelectionString(void);
+
+/*! @brief Returns the default `VisualID` used by GLFW.
+ *
+ *  @return The `VisualID` used by GLFW, or `NULL` if an
+ *  [error](@ref error_handling) occurred.
+ *
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED.
+ *
+ *  @thread_safety This function may be called from any thread.  Access is not
+ *  synchronized.
+ *
+ *  @since Added in version 3.4.
+ *
+ *  @ingroup native
+ */
+GLFWAPI VisualID glfwGetX11Visual(void);
+
+/*! @brief Returns the XCB connection used by GLFW, if any.
+ *
+ *  @return The XCB connection used by GLFW, or `NULL` if XCB is not used, or an
+ *  [error](@ref error_handling) occurred.
+ *
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED.
+ *
+ *  @thread_safety This function may be called from any thread.  Access is not
+ *  synchronized.
+ *
+ *  @since Added in version 3.4.
+ *
+ *  @ingroup native
+ */
+GLFWAPI xcb_connection_t* glfwGetXCBConnection(void);
 #endif
 
 #if defined(GLFW_EXPOSE_NATIVE_GLX)

src/x11_window.c

@@ -3351,5 +3351,44 @@ GLFWAPI const char* glfwGetX11SelectionString(void)
     return getSelectionString(_glfw.x11.PRIMARY);
 }
 
+GLFWAPI VisualID glfwGetX11Visual(void)
+{
+    _GLFW_REQUIRE_INIT_OR_RETURN(0);
+
+    if (_glfw.platform.platformID != GLFW_PLATFORM_X11)
+    {
+        _glfwInputError(GLFW_PLATFORM_UNAVAILABLE, "X11: Platform not initialized");
+        return 0;
+    }
+
+    return XVisualIDFromVisual(DefaultVisual(_glfw.x11.display, _glfw.x11.screen));
+}
+
+GLFWAPI xcb_connection_t* glfwGetXCBConnection(void)
+{
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    if (_glfw.platform.platformID != GLFW_PLATFORM_X11)
+    {
+        _glfwInputError(GLFW_PLATFORM_UNAVAILABLE, "X11: Platform not initialized");
+        return NULL;
+    }
+
+    if (!_glfw.x11.x11xcb.handle)
+    {
+        return NULL;
+    }
+
+    xcb_connection_t* connection = XGetXCBConnection(_glfw.x11.display);
+    if (!connection)
+    {
+        _glfwInputError(GLFW_PLATFORM_ERROR,
+                        "X11: Failed to retrieve XCB connection");
+        return NULL;
+    }
+
+    return connection;
+}
+
 #endif // _GLFW_X11