Add glfwGetEGLConfig native access function

This adds the glfwGetEGLConfig function for querying the EGLConfig of
the EGLSurface of a window.

This is a re-implementation of the PR #2045 by knokko, slightly
redesigned to handle EGLConfig being an opaque type in core EGL.

Closes #2045

CONTRIBUTORS.md

@@ -124,6 +124,7 @@ video tutorials.
  - Josh Kilmer
  - Byunghoon Kim
  - Cameron King
+ - knokko
  - Peter Knut
  - Christoph Kubisch
  - Yuri Kunde Schlesner

README.md

@@ -122,6 +122,7 @@ information on what to include when reporting a bug.
 
  - Added `GLFW_UNLIMITED_MOUSE_BUTTONS` input mode that allows mouse buttons beyond
    the limit of the mouse button tokens to be reported (#2423)
+ - Added `glfwGetEGLConfig` function to query the `EGLConfig` of a window (#2045)
  - Updated minimum CMake version to 3.16 (#2541)
  - Removed support for building with original MinGW (#2540)
  - [Win32] Removed support for Windows XP and Vista (#2505)

docs/news.md

@@ -14,6 +14,13 @@ values over 8. For compatibility with older versions, the
 @ref GLFW_UNLIMITED_MOUSE_BUTTONS input mode needs to be set to make use of
 this.
 
+
+### EGL config native access function {#eglconfig}
+
+GLFW now provides the @ref glfwGetEGLConfig native access function for querying
+the `EGLConfig` of a window that has a `EGLSurface`.
+
+
 ## Caveats {#caveats}
 
 ## Deprecations {#deprecations}
@@ -39,6 +46,9 @@ actively maintained and available on many platforms.
 
 ### New functions {#new_functions}
 
+ - @ref glfwGetEGLConfig
+
+
 ### New types {#new_types}
 
 ### New constants {#new_constants}

include/GLFW/glfw3native.h

@@ -586,6 +586,29 @@ GLFWAPI EGLContext glfwGetEGLContext(GLFWwindow* window);
  *  @ingroup native
  */
 GLFWAPI EGLSurface glfwGetEGLSurface(GLFWwindow* window);
+
+/*! @brief Retrieves the `EGLConfig` of the specified window's `EGLSurface`.
+ *
+ *  @param[in] window The window whose `EGLSurface` to query.
+ *  @param[out] config The `EGLConfig` of the window `EGLSurface`, if available.
+ *  @return `GLFW_TRUE` if successful, or `GLFW_FALSE` if an
+ *  [error](@ref error_handling) occurred.
+ *
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED and @ref
+ *  GLFW_NO_WINDOW_CONTEXT.
+ *
+ *  @remark `EGLConfig` is an opaque type.  Unlike other GLFW functions, the @p
+ *  config out parameter is not cleared on error, as core EGL does not define
+ *  any invalid value.
+ *
+ *  @thread_safety This function may be called from any thread.  Access is not
+ *  synchronized.
+ *
+ *  @since Added in version 3.5.
+ *
+ *  @ingroup native
+ */
+GLFWAPI int glfwGetEGLConfig(GLFWwindow* window, EGLConfig* config);
 #endif
 
 #if defined(GLFW_EXPOSE_NATIVE_OSMESA)

src/egl_context.c

@@ -946,3 +946,25 @@ GLFWAPI EGLSurface glfwGetEGLSurface(GLFWwindow* handle)
     return window->context.egl.surface;
 }
 
+GLFWAPI int glfwGetEGLConfig(GLFWwindow* handle, EGLConfig* config)
+{
+    _GLFW_REQUIRE_INIT_OR_RETURN(GLFW_FALSE);
+
+    _GLFWwindow* window = (_GLFWwindow*) handle;
+    assert(window != NULL);
+    assert(config != NULL);
+
+    if (window->context.source != GLFW_EGL_CONTEXT_API)
+    {
+        if (_glfw.platform.platformID != GLFW_PLATFORM_WAYLAND ||
+            window->context.source != GLFW_NATIVE_CONTEXT_API)
+        {
+            _glfwInputError(GLFW_NO_WINDOW_CONTEXT, NULL);
+            return GLFW_FALSE;
+        }
+    }
+
+    *config = window->context.egl.config;
+    return GLFW_TRUE;
+}
+