Added return by setters of previous callback.

include/GL/glfw3.h

@@ -908,6 +908,8 @@ GLFWAPI const char* glfwGetVersionString(void);
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @remarks This function may be called before @ref glfwInit.
  *
  *  @note The error callback is called by the thread where the error was
@@ -921,7 +923,7 @@ GLFWAPI const char* glfwGetVersionString(void);
  *
  *  @ingroup error
  */
-GLFWAPI void glfwSetErrorCallback(GLFWerrorfun cbfun);
+GLFWAPI GLFWerrorfun glfwSetErrorCallback(GLFWerrorfun cbfun);
 
 /*! @brief Returns the currently connected monitors.
  *
@@ -1005,12 +1007,13 @@ GLFWAPI const char* glfwGetMonitorName(GLFWmonitor* monitor);
  *
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
+ *  @return The previously set callback, or `NULL` if an error occurred.
  *
  *  @bug This callback is not yet called on monitor configuration changes.
  *
  *  @ingroup monitor
  */
-GLFWAPI void glfwSetMonitorCallback(GLFWmonitorfun cbfun);
+GLFWAPI GLFWmonitorfun glfwSetMonitorCallback(GLFWmonitorfun cbfun);
 
 /*! @brief Returns the available video modes for the specified monitor.
  *
@@ -1502,9 +1505,11 @@ GLFWAPI void* glfwGetWindowUserPointer(GLFWwindow* window);
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup window
  */
-GLFWAPI void glfwSetWindowPosCallback(GLFWwindow* window, GLFWwindowposfun cbfun);
+GLFWAPI GLFWwindowposfun glfwSetWindowPosCallback(GLFWwindow* window, GLFWwindowposfun cbfun);
 
 /*! @brief Sets the size callback for the specified window.
  *
@@ -1516,9 +1521,11 @@ GLFWAPI void glfwSetWindowPosCallback(GLFWwindow* window, GLFWwindowposfun cbfun
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup window
  */
-GLFWAPI void glfwSetWindowSizeCallback(GLFWwindow* window, GLFWwindowsizefun cbfun);
+GLFWAPI GLFWwindowsizefun glfwSetWindowSizeCallback(GLFWwindow* window, GLFWwindowsizefun cbfun);
 
 /*! @brief Sets the close callback for the specified window.
  *
@@ -1536,12 +1543,14 @@ GLFWAPI void glfwSetWindowSizeCallback(GLFWwindow* window, GLFWwindowsizefun cbf
  *  @remarks Calling @ref glfwDestroyWindow does not cause this callback to be
  *  called.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @remarks **Mac OS X:** Selecting Quit from the application menu will
  *  trigger the close callback for all windows.
  *
  *  @ingroup window
  */
-GLFWAPI void glfwSetWindowCloseCallback(GLFWwindow* window, GLFWwindowclosefun cbfun);
+GLFWAPI GLFWwindowclosefun glfwSetWindowCloseCallback(GLFWwindow* window, GLFWwindowclosefun cbfun);
 
 /*! @brief Sets the refresh callback for the specified window.
  *
@@ -1556,10 +1565,15 @@ GLFWAPI void glfwSetWindowCloseCallback(GLFWwindow* window, GLFWwindowclosefun c
  *  @param[in] window The window whose callback to set.
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
+ *  @note On compositing window systems such as Aero, Compiz or Aqua, where the
+ *  window contents are saved off-screen, this callback may be called only very
+ *  infrequently or never at all.
  *
  *  @ingroup window
  */
-GLFWAPI void glfwSetWindowRefreshCallback(GLFWwindow* window, GLFWwindowrefreshfun cbfun);
+GLFWAPI GLFWwindowrefreshfun glfwSetWindowRefreshCallback(GLFWwindow* window, GLFWwindowrefreshfun cbfun);
 
 /*! @brief Sets the focus callback for the specified window.
  *
@@ -1570,9 +1584,11 @@ GLFWAPI void glfwSetWindowRefreshCallback(GLFWwindow* window, GLFWwindowrefreshf
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup window
  */
-GLFWAPI void glfwSetWindowFocusCallback(GLFWwindow* window, GLFWwindowfocusfun cbfun);
+GLFWAPI GLFWwindowfocusfun glfwSetWindowFocusCallback(GLFWwindow* window, GLFWwindowfocusfun cbfun);
 
 /*! @brief Sets the iconify callback for the specified window.
  *
@@ -1583,9 +1599,11 @@ GLFWAPI void glfwSetWindowFocusCallback(GLFWwindow* window, GLFWwindowfocusfun c
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup window
  */
-GLFWAPI void glfwSetWindowIconifyCallback(GLFWwindow* window, GLFWwindowiconifyfun cbfun);
+GLFWAPI GLFWwindowiconifyfun glfwSetWindowIconifyCallback(GLFWwindow* window, GLFWwindowiconifyfun cbfun);
 
 /*! @brief Processes all pending events.
  *
@@ -1786,9 +1804,11 @@ GLFWAPI void glfwSetCursorPos(GLFWwindow* window, double xpos, double ypos);
  *  @param[in] cbfun The new key callback, or `NULL` to remove the currently
  *  set callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup input
  */
-GLFWAPI void glfwSetKeyCallback(GLFWwindow* window, GLFWkeyfun cbfun);
+GLFWAPI GLFWkeyfun glfwSetKeyCallback(GLFWwindow* window, GLFWkeyfun cbfun);
 
 /*! @brief Sets the Unicode character callback.
  *
@@ -1803,9 +1823,11 @@ GLFWAPI void glfwSetKeyCallback(GLFWwindow* window, GLFWkeyfun cbfun);
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup input
  */
-GLFWAPI void glfwSetCharCallback(GLFWwindow* window, GLFWcharfun cbfun);
+GLFWAPI GLFWcharfun glfwSetCharCallback(GLFWwindow* window, GLFWcharfun cbfun);
 
 /*! @brief Sets the mouse button callback.
  *
@@ -1816,9 +1838,11 @@ GLFWAPI void glfwSetCharCallback(GLFWwindow* window, GLFWcharfun cbfun);
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup input
  */
-GLFWAPI void glfwSetMouseButtonCallback(GLFWwindow* window, GLFWmousebuttonfun cbfun);
+GLFWAPI GLFWmousebuttonfun glfwSetMouseButtonCallback(GLFWwindow* window, GLFWmousebuttonfun cbfun);
 
 /*! @brief Sets the cursor position callback.
  *
@@ -1830,9 +1854,11 @@ GLFWAPI void glfwSetMouseButtonCallback(GLFWwindow* window, GLFWmousebuttonfun c
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup input
  */
-GLFWAPI void glfwSetCursorPosCallback(GLFWwindow* window, GLFWcursorposfun cbfun);
+GLFWAPI GLFWcursorposfun glfwSetCursorPosCallback(GLFWwindow* window, GLFWcursorposfun cbfun);
 
 /*! @brief Sets the cursor enter/exit callback.
  *
@@ -1844,9 +1870,11 @@ GLFWAPI void glfwSetCursorPosCallback(GLFWwindow* window, GLFWcursorposfun cbfun
  *  @param[in] cbfun The new callback, or `NULL` to remove the currently set
  *  callback.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup input
  */
-GLFWAPI void glfwSetCursorEnterCallback(GLFWwindow* window, GLFWcursorenterfun cbfun);
+GLFWAPI GLFWcursorenterfun glfwSetCursorEnterCallback(GLFWwindow* window, GLFWcursorenterfun cbfun);
 
 /*! @brief Sets the scroll callback.
  *
@@ -1861,9 +1889,11 @@ GLFWAPI void glfwSetCursorEnterCallback(GLFWwindow* window, GLFWcursorenterfun c
  *  @remarks This receives all scrolling input, like that from a mouse wheel or
  *  a touchpad scrolling area.
  *
+ *  @return The previously set callback, or `NULL` if an error occurred.
+ *
  *  @ingroup input
  */
-GLFWAPI void glfwSetScrollCallback(GLFWwindow* window, GLFWscrollfun cbfun);
+GLFWAPI GLFWscrollfun glfwSetScrollCallback(GLFWwindow* window, GLFWscrollfun cbfun);
 
 /*! @brief Returns a parameter of the specified joystick.
  *

src/init.c

@@ -190,8 +190,10 @@ GLFWAPI const char* glfwGetVersionString(void)
     return _glfwPlatformGetVersionString();
 }
 
-GLFWAPI void glfwSetErrorCallback(GLFWerrorfun cbfun)
+GLFWAPI GLFWerrorfun glfwSetErrorCallback(GLFWerrorfun cbfun)
 {
+    GLFWerrorfun previous = _glfwErrorCallback;
     _glfwErrorCallback = cbfun;
+    return previous;
 }
 

src/input.c

@@ -337,45 +337,79 @@ GLFWAPI void glfwSetCursorPos(GLFWwindow* handle, double xpos, double ypos)
     _glfwPlatformSetCursorPos(window, xpos, ypos);
 }
 
-GLFWAPI void glfwSetKeyCallback(GLFWwindow* handle, GLFWkeyfun cbfun)
+GLFWAPI GLFWkeyfun glfwSetKeyCallback(GLFWwindow* handle, GLFWkeyfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWkeyfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.key;
     window->callbacks.key = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetCharCallback(GLFWwindow* handle, GLFWcharfun cbfun)
+GLFWAPI GLFWcharfun glfwSetCharCallback(GLFWwindow* handle, GLFWcharfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWcharfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.character;
     window->callbacks.character = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetMouseButtonCallback(GLFWwindow* handle, GLFWmousebuttonfun cbfun)
+GLFWAPI GLFWmousebuttonfun glfwSetMouseButtonCallback(GLFWwindow* handle,
+                                                      GLFWmousebuttonfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWmousebuttonfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.mouseButton;
     window->callbacks.mouseButton = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetCursorPosCallback(GLFWwindow* handle, GLFWcursorposfun cbfun)
+GLFWAPI GLFWcursorposfun glfwSetCursorPosCallback(GLFWwindow* handle,
+                                                  GLFWcursorposfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWcursorposfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.cursorPos;
     window->callbacks.cursorPos = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetCursorEnterCallback(GLFWwindow* handle, GLFWcursorenterfun cbfun)
+GLFWAPI GLFWcursorenterfun glfwSetCursorEnterCallback(GLFWwindow* handle,
+                                                      GLFWcursorenterfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWcursorenterfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.cursorEnter;
     window->callbacks.cursorEnter = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetScrollCallback(GLFWwindow* handle, GLFWscrollfun cbfun)
+GLFWAPI GLFWscrollfun glfwSetScrollCallback(GLFWwindow* handle,
+                                            GLFWscrollfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWscrollfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.scroll;
     window->callbacks.scroll = cbfun;
+    return previous;
 }
 

src/monitor.c

@@ -289,10 +289,14 @@ GLFWAPI const char* glfwGetMonitorName(GLFWmonitor* handle)
     return monitor->name;
 }
 
-GLFWAPI void glfwSetMonitorCallback(GLFWmonitorfun cbfun)
+GLFWAPI GLFWmonitorfun glfwSetMonitorCallback(GLFWmonitorfun cbfun)
 {
-    _GLFW_REQUIRE_INIT();
+    GLFWmonitorfun previous;
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = _glfw.monitorCallback;
     _glfw.monitorCallback = cbfun;
+    return previous;
 }
 
 GLFWAPI const GLFWvidmode* glfwGetVideoModes(GLFWmonitor* handle, int* count)

src/window.c

@@ -582,46 +582,82 @@ GLFWAPI void* glfwGetWindowUserPointer(GLFWwindow* handle)
     return window->userPointer;
 }
 
-GLFWAPI void glfwSetWindowPosCallback(GLFWwindow* handle, GLFWwindowposfun cbfun)
+GLFWAPI GLFWwindowposfun glfwSetWindowPosCallback(GLFWwindow* handle,
+                                                  GLFWwindowposfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWwindowposfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.pos;
     window->callbacks.pos = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetWindowSizeCallback(GLFWwindow* handle, GLFWwindowsizefun cbfun)
+GLFWAPI GLFWwindowsizefun glfwSetWindowSizeCallback(GLFWwindow* handle,
+                                                    GLFWwindowsizefun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWwindowsizefun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.size;
     window->callbacks.size = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetWindowCloseCallback(GLFWwindow* handle, GLFWwindowclosefun cbfun)
+GLFWAPI GLFWwindowclosefun glfwSetWindowCloseCallback(GLFWwindow* handle,
+                                                      GLFWwindowclosefun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWwindowclosefun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.close;
     window->callbacks.close = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetWindowRefreshCallback(GLFWwindow* handle, GLFWwindowrefreshfun cbfun)
+GLFWAPI GLFWwindowrefreshfun glfwSetWindowRefreshCallback(GLFWwindow* handle,
+                                                          GLFWwindowrefreshfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWwindowrefreshfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.refresh;
     window->callbacks.refresh = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetWindowFocusCallback(GLFWwindow* handle, GLFWwindowfocusfun cbfun)
+GLFWAPI GLFWwindowfocusfun glfwSetWindowFocusCallback(GLFWwindow* handle,
+                                                      GLFWwindowfocusfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWwindowfocusfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.focus;
     window->callbacks.focus = cbfun;
+    return previous;
 }
 
-GLFWAPI void glfwSetWindowIconifyCallback(GLFWwindow* handle, GLFWwindowiconifyfun cbfun)
+GLFWAPI GLFWwindowiconifyfun glfwSetWindowIconifyCallback(GLFWwindow* handle,
+                                                          GLFWwindowiconifyfun cbfun)
 {
     _GLFWwindow* window = (_GLFWwindow*) handle;
-    _GLFW_REQUIRE_INIT();
+    GLFWwindowiconifyfun previous;
+
+    _GLFW_REQUIRE_INIT_OR_RETURN(NULL);
+
+    previous = window->callbacks.iconify;
     window->callbacks.iconify = cbfun;
+    return previous;
 }
 
 GLFWAPI void glfwPollEvents(void)