Query work area for X11

The function ```glfwGetMonitorWorkarea``` retrieves the rectangle work
area of the specified monitor.

examples/simple.c

@@ -79,6 +79,7 @@ int main(void)
     GLFWwindow* window;
     GLuint vertex_buffer, vertex_shader, fragment_shader, program;
     GLint mvp_location, vpos_location, vcol_location;
+    int workarea_x, workarea_y, workarea_width, workarea_height;
 
     glfwSetErrorCallback(error_callback);
 
@@ -131,6 +132,8 @@ int main(void)
     glVertexAttribPointer(vcol_location, 3, GL_FLOAT, GL_FALSE,
                           sizeof(vertices[0]), (void*) (sizeof(float) * 2));
 
+    glfwGetMonitorWorkarea(glfwGetPrimaryMonitor(), &workarea_x, &workarea_y, &workarea_width, &workarea_height);
+    printf("Monitor work area: %d, %d, %d, %d\n", workarea_x, workarea_y, workarea_width, workarea_height);
     while (!glfwWindowShouldClose(window))
     {
         float ratio;

include/GLFW/glfw3.h

@@ -1719,6 +1719,31 @@ GLFWAPI GLFWmonitor* glfwGetPrimaryMonitor(void);
  */
 GLFWAPI void glfwGetMonitorPos(GLFWmonitor* monitor, int* xpos, int* ypos);
 
+/*! @brief Returns the work area of the monitor.
+ *
+ *  This function returns the position, in screen coordinates, of the upper-left
+ *  corner of the specified monitor.
+ *
+ *  Any or all of the position arguments may be `NULL`.  If an error occurs, all
+ *  non-`NULL` position arguments will be set to zero.
+ *
+ *  @param[in] monitor The monitor to query.
+ *  @param[out] xpos Where to store the monitor x-coordinate, or `NULL`.
+ *  @param[out] ypos Where to store the monitor y-coordinate, or `NULL`.
+ *
+ *  @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.
+ *
+ *  @sa @ref monitor_properties
+ *
+ *  @since Added in version 3.0.
+ *
+ *  @ingroup monitor
+ */
+GLFWAPI void glfwGetMonitorWorkarea(GLFWmonitor* monitor, int* xpos, int* ypos, int *width, int *height);
+
 /*! @brief Returns the physical size of the monitor.
  *
  *  This function returns the size, in millimetres, of the display area of the

src/internal.h

@@ -597,6 +597,7 @@ const char* _glfwPlatformGetKeyName(int key, int scancode);
 int _glfwPlatformGetKeyScancode(int key);
 
 void _glfwPlatformGetMonitorPos(_GLFWmonitor* monitor, int* xpos, int* ypos);
+void _glfwPlatformGetMonitorWorkarea(_GLFWmonitor* monitor, int* xpos, int* ypos, int *width, int *height);
 GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* count);
 void _glfwPlatformGetVideoMode(_GLFWmonitor* monitor, GLFWvidmode* mode);
 void _glfwPlatformGetGammaRamp(_GLFWmonitor* monitor, GLFWgammaramp* ramp);

src/monitor.c

@@ -296,6 +296,25 @@ GLFWAPI void glfwGetMonitorPos(GLFWmonitor* handle, int* xpos, int* ypos)
     _glfwPlatformGetMonitorPos(monitor, xpos, ypos);
 }
 
+GLFWAPI void glfwGetMonitorWorkarea(GLFWmonitor* handle, int* xpos, int* ypos, int* width, int* height)
+{
+    _GLFWmonitor* monitor = (_GLFWmonitor*) handle;
+    assert(monitor != NULL);
+
+    if (xpos)
+        *xpos = 0;
+    if (ypos)
+        *ypos = 0;
+    if (width)
+        *width = 0;
+    if (width)
+        *width = 0;
+
+    _GLFW_REQUIRE_INIT();
+
+    _glfwPlatformGetMonitorWorkarea(monitor, xpos, ypos, width, height);
+}
+
 GLFWAPI void glfwGetMonitorPhysicalSize(GLFWmonitor* handle, int* widthMM, int* heightMM)
 {
     _GLFWmonitor* monitor = (_GLFWmonitor*) handle;

src/null_monitor.c

@@ -36,6 +36,10 @@ void _glfwPlatformGetMonitorPos(_GLFWmonitor* monitor, int* xpos, int* ypos)
 {
 }
 
+void _glfwPlatformGetMonitorWorkarea(_GLFWmonitor* monitor, int* xpos, int* ypos, int *width, int *height)
+{
+}
+
 GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* found)
 {
     return NULL;

src/x11_monitor.c

@@ -338,6 +338,38 @@ void _glfwPlatformGetMonitorPos(_GLFWmonitor* monitor, int* xpos, int* ypos)
     }
 }
 
+void _glfwPlatformGetMonitorWorkarea(_GLFWmonitor* monitor, int* xpos, int* ypos, int *width, int *height)
+{
+    if (_glfw.x11.randr.available && !_glfw.x11.randr.monitorBroken)
+    {
+        Atom workarea = XInternAtom(_glfw.x11.display, "_NET_WORKAREA", True);
+        Atom type;
+        int format;
+        unsigned long num;
+        unsigned long bytesLeft;
+        unsigned long *workareaValues;
+        unsigned char *data = NULL;
+
+        if(workarea == None)
+            return;
+
+        if (XGetWindowProperty(_glfw.x11.display, _glfw.x11.root, workarea, 0,
+                               4 * 32, False, AnyPropertyType, &type, &format,
+                               &num, &bytesLeft, &data) != Success) {
+            return;
+        }
+
+        if(type == None || format == 0 || bytesLeft || num % 4)
+            return;
+
+        workareaValues = (unsigned long*)data;
+        *xpos = workareaValues[0];
+        *ypos = workareaValues[1];
+        *width = workareaValues[2];
+        *height = workareaValues[3];
+    }
+}
+
 GLFWvidmode* _glfwPlatformGetVideoModes(_GLFWmonitor* monitor, int* count)
 {
     GLFWvidmode* result;