Added glfwDragWindow function to latest platform structure

Based on work by Felipe da Silva (felselva) #987 ported to v3.4

Add a function glfwDragWindow that starts a drag operation for the
specified window. The implementation is done for X11, Windows, and
requires tests on Wayland. Patch is related with the issue #923.

README.md

@@ -121,6 +121,7 @@ information on what to include when reporting a bug.
 
 ## Changelog
 
+ - Added `glfwDragWindow` function for starting a drag operation on a window
  - 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

examples/windows.c

@@ -31,6 +31,12 @@
 #include <stdio.h>
 #include <stdlib.h>
 
+void mouse_button_callback(GLFWwindow* window, int button, int action, int mods){
+    if(button == GLFW_MOUSE_BUTTON_LEFT && action == GLFW_PRESS){
+        glfwDragWindow(window);
+    }
+}
+
 int main(int argc, char** argv)
 {
     int xpos, ypos, height;
@@ -79,6 +85,7 @@ int main(int argc, char** argv)
                          xpos + size * (1 + (i & 1)),
                          ypos + size * (1 + (i >> 1)));
         glfwSetInputMode(windows[i], GLFW_STICKY_KEYS, GLFW_TRUE);
+        glfwSetMouseButtonCallback(windows[i], mouse_button_callback);
 
         glfwMakeContextCurrent(windows[i]);
         gladLoadGL(glfwGetProcAddress);

include/GLFW/glfw3.h

@@ -3842,6 +3842,23 @@ GLFWAPI void glfwHideWindow(GLFWwindow* window);
  */
 GLFWAPI void glfwFocusWindow(GLFWwindow* window);
 
+/*! @brief Starts drag operation to the specified window.
+ *
+ *  This function starts the drag operation of the specified window.
+ *
+ *  @param[in] window The window to start the dragging operation.
+ *
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED and @ref
+ *  GLFW_PLATFORM_ERROR.
+ *
+ *  @thread_safety This function must only be called from the main thread.
+ *
+ *  @since Added in version 3.4.
+ *
+ *  @ingroup window
+ */
+GLFWAPI void glfwDragWindow(GLFWwindow* handle);
+
 /*! @brief Requests user attention to the specified window.
  *
  *  This function requests user attention to the specified window.  On

src/cocoa_init.m

@@ -541,6 +541,7 @@ GLFWbool _glfwConnectCocoa(int platformID, _GLFWplatform* platform)
         _glfwHideWindowCocoa,
         _glfwRequestWindowAttentionCocoa,
         _glfwFocusWindowCocoa,
+        _glfwDragWindowCocoa,
         _glfwSetWindowMonitorCocoa,
         _glfwWindowFocusedCocoa,
         _glfwWindowIconifiedCocoa,

src/cocoa_platform.h

@@ -234,6 +234,7 @@ void _glfwShowWindowCocoa(_GLFWwindow* window);
 void _glfwHideWindowCocoa(_GLFWwindow* window);
 void _glfwRequestWindowAttentionCocoa(_GLFWwindow* window);
 void _glfwFocusWindowCocoa(_GLFWwindow* window);
+void _glfwDragWindowCocoa(_GLFWwindow* window);
 void _glfwSetWindowMonitorCocoa(_GLFWwindow* window, _GLFWmonitor* monitor, int xpos, int ypos, int width, int height, int refreshRate);
 GLFWbool _glfwWindowFocusedCocoa(_GLFWwindow* window);
 GLFWbool _glfwWindowIconifiedCocoa(_GLFWwindow* window);

src/cocoa_window.m

@@ -1218,6 +1218,11 @@ void _glfwFocusWindowCocoa(_GLFWwindow* window)
     } // autoreleasepool
 }
 
+void _glfwDragWindowCocoa(_GLFWwindow* window)
+{
+    // TODO
+}
+
 void _glfwSetWindowMonitorCocoa(_GLFWwindow* window,
                                 _GLFWmonitor* monitor,
                                 int xpos, int ypos,

src/internal.h

@@ -724,6 +724,7 @@ struct _GLFWplatform
     void (*hideWindow)(_GLFWwindow*);
     void (*requestWindowAttention)(_GLFWwindow*);
     void (*focusWindow)(_GLFWwindow*);
+    void (*dragWindow)(_GLFWwindow*);
     void (*setWindowMonitor)(_GLFWwindow*,_GLFWmonitor*,int,int,int,int,int);
     GLFWbool (*windowFocused)(_GLFWwindow*);
     GLFWbool (*windowIconified)(_GLFWwindow*);

src/null_init.c

@@ -89,6 +89,7 @@ GLFWbool _glfwConnectNull(int platformID, _GLFWplatform* platform)
         _glfwHideWindowNull,
         _glfwRequestWindowAttentionNull,
         _glfwFocusWindowNull,
+        _glfwDragWindowNull,
         _glfwSetWindowMonitorNull,
         _glfwWindowFocusedNull,
         _glfwWindowIconifiedNull,

src/null_platform.h

@@ -118,6 +118,7 @@ void _glfwRequestWindowAttentionNull(_GLFWwindow* window);
 void _glfwRequestWindowAttentionNull(_GLFWwindow* window);
 void _glfwHideWindowNull(_GLFWwindow* window);
 void _glfwFocusWindowNull(_GLFWwindow* window);
+void _glfwDragWindowNull(_GLFWwindow* window);
 GLFWbool _glfwWindowFocusedNull(_GLFWwindow* window);
 GLFWbool _glfwWindowIconifiedNull(_GLFWwindow* window);
 GLFWbool _glfwWindowVisibleNull(_GLFWwindow* window);

src/null_window.c

@@ -461,6 +461,11 @@ void _glfwFocusWindowNull(_GLFWwindow* window)
     _glfwInputWindowFocus(window, GLFW_TRUE);
 }
 
+void _glfwDragWindowNull(_GLFWwindow* window)
+{
+    // TODO
+}
+
 GLFWbool _glfwWindowFocusedNull(_GLFWwindow* window)
 {
     return _glfw.null.focusedWindow == window;

src/win32_init.c

@@ -652,6 +652,7 @@ GLFWbool _glfwConnectWin32(int platformID, _GLFWplatform* platform)
         _glfwHideWindowWin32,
         _glfwRequestWindowAttentionWin32,
         _glfwFocusWindowWin32,
+        _glfwDragWindowWin32,
         _glfwSetWindowMonitorWin32,
         _glfwWindowFocusedWin32,
         _glfwWindowIconifiedWin32,

src/win32_platform.h

@@ -557,6 +557,7 @@ void _glfwShowWindowWin32(_GLFWwindow* window);
 void _glfwHideWindowWin32(_GLFWwindow* window);
 void _glfwRequestWindowAttentionWin32(_GLFWwindow* window);
 void _glfwFocusWindowWin32(_GLFWwindow* window);
+void _glfwDragWindowWin32(_GLFWwindow* window);
 void _glfwSetWindowMonitorWin32(_GLFWwindow* window, _GLFWmonitor* monitor, int xpos, int ypos, int width, int height, int refreshRate);
 GLFWbool _glfwWindowFocusedWin32(_GLFWwindow* window);
 GLFWbool _glfwWindowIconifiedWin32(_GLFWwindow* window);

src/win32_window.c

@@ -1751,6 +1751,12 @@ void _glfwFocusWindowWin32(_GLFWwindow* window)
     SetFocus(window->win32.handle);
 }
 
+void _glfwDragWindowWin32(_GLFWwindow* window)
+{
+    ReleaseCapture();
+    SendMessage(window->win32.handle, WM_NCLBUTTONDOWN, HTCAPTION, 0);
+}
+
 void _glfwSetWindowMonitorWin32(_GLFWwindow* window,
                                 _GLFWmonitor* monitor,
                                 int xpos, int ypos,

src/window.c

@@ -833,6 +833,16 @@ GLFWAPI void glfwFocusWindow(GLFWwindow* handle)
     _glfw.platform.focusWindow(window);
 }
 
+GLFWAPI void glfwDragWindow(GLFWwindow* handle)
+{
+    _GLFWwindow* window = (_GLFWwindow*) handle;
+    assert(window != NULL);
+
+    _GLFW_REQUIRE_INIT();
+
+    _glfw.platform.dragWindow(window);
+}
+
 GLFWAPI int glfwGetWindowAttrib(GLFWwindow* handle, int attrib)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;

src/wl_init.c

@@ -401,6 +401,7 @@ GLFWbool _glfwConnectWayland(int platformID, _GLFWplatform* platform)
         _glfwHideWindowWayland,
         _glfwRequestWindowAttentionWayland,
         _glfwFocusWindowWayland,
+        _glfwDragWindowWayland,
         _glfwSetWindowMonitorWayland,
         _glfwWindowFocusedWayland,
         _glfwWindowIconifiedWayland,

src/wl_platform.h

@@ -462,6 +462,7 @@ void _glfwShowWindowWayland(_GLFWwindow* window);
 void _glfwHideWindowWayland(_GLFWwindow* window);
 void _glfwRequestWindowAttentionWayland(_GLFWwindow* window);
 void _glfwFocusWindowWayland(_GLFWwindow* window);
+void _glfwDragWindowWayland(_GLFWwindow* window);
 void _glfwSetWindowMonitorWayland(_GLFWwindow* window, _GLFWmonitor* monitor, int xpos, int ypos, int width, int height, int refreshRate);
 GLFWbool _glfwWindowFocusedWayland(_GLFWwindow* window);
 GLFWbool _glfwWindowIconifiedWayland(_GLFWwindow* window);

src/wl_window.c

@@ -2087,6 +2087,11 @@ void _glfwFocusWindowWayland(_GLFWwindow* window)
                     "Wayland: The platform does not support setting the input focus");
 }
 
+void _glfwDragWindowWayland(_GLFWwindow* window)
+{
+    wl_shell_surface_move(window->wl.shellSurface, _glfw.wl.seat, _glfw.wl.pointerSerial);
+}
+
 void _glfwSetWindowMonitorWayland(_GLFWwindow* window,
                                   _GLFWmonitor* monitor,
                                   int xpos, int ypos,

src/x11_init.c

@@ -1223,6 +1223,7 @@ GLFWbool _glfwConnectX11(int platformID, _GLFWplatform* platform)
         _glfwHideWindowX11,
         _glfwRequestWindowAttentionX11,
         _glfwFocusWindowX11,
+        _glfwDragWindowX11,
         _glfwSetWindowMonitorX11,
         _glfwWindowFocusedX11,
         _glfwWindowIconifiedX11,

src/x11_platform.h

@@ -922,6 +922,7 @@ void _glfwShowWindowX11(_GLFWwindow* window);
 void _glfwHideWindowX11(_GLFWwindow* window);
 void _glfwRequestWindowAttentionX11(_GLFWwindow* window);
 void _glfwFocusWindowX11(_GLFWwindow* window);
+void _glfwDragWindowX11(_GLFWwindow* window);
 void _glfwSetWindowMonitorX11(_GLFWwindow* window, _GLFWmonitor* monitor, int xpos, int ypos, int width, int height, int refreshRate);
 GLFWbool _glfwWindowFocusedX11(_GLFWwindow* window);
 GLFWbool _glfwWindowIconifiedX11(_GLFWwindow* window);

src/x11_window.c

@@ -45,6 +45,7 @@
 #define _NET_WM_STATE_REMOVE        0
 #define _NET_WM_STATE_ADD           1
 #define _NET_WM_STATE_TOGGLE        2
+#define _NET_WM_MOVERESIZE_MOVE     8
 
 // Additional mouse button names for XButtonEvent
 #define Button6            6
@@ -2405,6 +2406,28 @@ void _glfwFocusWindowX11(_GLFWwindow* window)
     XFlush(_glfw.x11.display);
 }
 
+void _glfwDragWindowX11(_GLFWwindow* window)
+{
+    int winXpos, winYpos;
+    double curXpos, curYpos;
+    XClientMessageEvent xclient;
+    memset(&xclient, 0, sizeof(XClientMessageEvent));
+    XUngrabPointer(_glfw.x11.display, 0);
+    XFlush(_glfw.x11.display);
+    _glfwGetCursorPosX11(window, &curXpos, &curYpos);
+    _glfwGetWindowPosX11(window, &winXpos, &winYpos);
+    xclient.type = ClientMessage;
+    xclient.window = window->x11.handle;
+    xclient.message_type = XInternAtom(_glfw.x11.display, "_NET_WM_MOVERESIZE", False);
+    xclient.format = 32;
+    xclient.data.l[0] = winXpos + curXpos;
+    xclient.data.l[1] = winYpos + curYpos;
+    xclient.data.l[2] = _NET_WM_MOVERESIZE_MOVE;
+    xclient.data.l[3] = 0;
+    xclient.data.l[4] = 0;
+    XSendEvent(_glfw.x11.display, _glfw.x11.root, False, SubstructureRedirectMask | SubstructureNotifyMask, (XEvent *)&xclient);
+}
+
 void _glfwSetWindowMonitorX11(_GLFWwindow* window,
                               _GLFWmonitor* monitor,
                               int xpos, int ypos,