integrate _glfwGetWindowIsFullscreenX11 with platform idiom

src/internal.h

@@ -747,7 +747,7 @@ struct _GLFWplatform
     void (*setWindowFloating)(_GLFWwindow*,GLFWbool);
     void (*setWindowOpacity)(_GLFWwindow*,float);
     void (*setWindowMousePassthrough)(_GLFWwindow*,GLFWbool);
-    void (*getWindowIsFullscreen) (_GLFWwindow*);
+    GLFWbool (*getWindowIsFullscreen) (_GLFWwindow*);
     void (*pollEvents)(void);
     void (*waitEvents)(void);
     void (*waitEventsTimeout)(double);

src/window.c

@@ -173,10 +173,6 @@ void _glfwInputWindowMonitor(_GLFWwindow* window, _GLFWmonitor* monitor)
     window->monitor = monitor;
 }
 
-GLFWbool _glfwWindowGetIsFullscreen(_GLFWwindow* window) {
-    return _glfwGetIsWindowFullscreenX11(window);
-}
-
 //////////////////////////////////////////////////////////////////////////
 //////                        GLFW public API                       //////
 //////////////////////////////////////////////////////////////////////////
@@ -905,7 +901,7 @@ GLFWAPI int glfwGetWindowAttrib(GLFWwindow* handle, int attrib)
         case GLFW_MOUSE_PASSTHROUGH:
             return window->mousePassthrough;
         case GLFW_FULLSCREEN:
-            return _glfwWindowGetIsFullscreen(window);
+            return _glfw.platform.getWindowIsFullscreen(window);
         case GLFW_TRANSPARENT_FRAMEBUFFER:
             return _glfw.platform.framebufferTransparent(window);
         case GLFW_RESIZABLE:

src/x11_init.c

@@ -1237,6 +1237,7 @@ GLFWbool _glfwConnectX11(int platformID, _GLFWplatform* platform)
         .setWindowFloating = _glfwSetWindowFloatingX11,
         .setWindowOpacity = _glfwSetWindowOpacityX11,
         .setWindowMousePassthrough = _glfwSetWindowMousePassthroughX11,
+        .getWindowIsFullscreen = _glfwGetWindowIsFullscreenX11,
         .pollEvents = _glfwPollEventsX11,
         .waitEvents = _glfwWaitEventsX11,
         .waitEventsTimeout = _glfwWaitEventsTimeoutX11,

src/x11_platform.h

@@ -934,7 +934,7 @@ void _glfwSetWindowFloatingX11(_GLFWwindow* window, GLFWbool enabled);
 float _glfwGetWindowOpacityX11(_GLFWwindow* window);
 void _glfwSetWindowOpacityX11(_GLFWwindow* window, float opacity);
 void _glfwSetWindowMousePassthroughX11(_GLFWwindow* window, GLFWbool enabled);
-GLFWbool _glfwGetIsWindowFullscreenX11(_GLFWwindow* window);
+GLFWbool _glfwGetWindowIsFullscreenX11(_GLFWwindow* window);
 
 void _glfwSetRawMouseMotionX11(_GLFWwindow *window, GLFWbool enabled);
 GLFWbool _glfwRawMouseMotionSupportedX11(void);

src/x11_window.c

@@ -26,7 +26,9 @@
 //========================================================================
 
 #include "internal.h"
+#include <X11/X.h>
 #include <X11/Xlib.h>
+#include <X11/Xutil.h>
 
 #if defined(_GLFW_X11)
 
@@ -2730,25 +2732,44 @@ void _glfwSetWindowMousePassthroughX11(_GLFWwindow* window, GLFWbool enabled)
     }
 }
 
-GLFWbool _glfwGetIsWindowFullscreenX11(_GLFWwindow* window)
+GLFWbool _glfwGetWindowIsFullscreenX11(_GLFWwindow* window)
 {
-    Atom atom = XInternAtom(_glfw.x11.display, "_NET_WM_STATE_FULLSCREEN", 0);
+    Atom wm_state = XInternAtom(_glfw.x11.display, "_NET_WM_STATE", True);
+    Atom wm_state_fullscreen = XInternAtom(_glfw.x11.display, "_NET_WM_STATE_FULLSCREEN", True);
 
-    unsigned char prop[32] = {};
-    XGetWindowProperty(
+    Atom type = XA_ATOM;
+    int format;
+    size_t nItems;
+    size_t bytesAfterReturn;
+    Atom* prop;
+    
+    int result = XGetWindowProperty(
         _glfw.x11.display,
         window->x11.handle,
-        atom, 
+        wm_state, 
         0,
-        1, // 32 bits
-        0,
-        NULL,
-        NULL,
-        NULL,
-        NULL,
-        NULL,
-        (unsigned char**)&prop
+        ~0L,
+        False,
+        AnyPropertyType,
+        &type,
+        &format,
+        &nItems,
+        &bytesAfterReturn,
+        (unsigned char**)&prop 
     );
+
+    assert(result == Success);
+
+    GLFWbool isFullscreen = 0;
+    for (int i = 0; i < nItems; i++) {
+        if (prop[i] == wm_state_fullscreen) {
+            isFullscreen = 1;
+        }
+    }
+
+    XFree(prop);
+    
+    return isFullscreen;
 }
 
 float _glfwGetWindowOpacityX11(_GLFWwindow* window)

tests/window.c

@@ -190,6 +190,15 @@ int main(int argc, char** argv)
                     glfwSetWindowAttrib(window, GLFW_MOUSE_PASSTHROUGH, false);
             }
 
+            if (nk_button_label(nk, "Is window fullscreen?")) {
+                int fullscreen = glfwGetWindowAttrib(window, GLFW_FULLSCREEN);
+                if (fullscreen) {
+                    nk_label(nk, "Yes", NK_TEXT_CENTERED); 
+                } else {
+                    nk_label(nk, "No", NK_TEXT_CENTERED); 
+                }
+            }
+
             nk_label(nk, "Press Enter in a text field to set value", NK_TEXT_CENTERED);
 
             nk_flags events;