Add GLFW_COCOA_GRAPHICS_SWICTHING

This provides control over whether the context should participate in
macOS Automatic Graphics Switching.

Closes #377.
Closes #935.

src/cocoa_window.m

@@ -340,6 +340,14 @@ static const NSRange kEmptyRange = { NSNotFound, 0 };
 
 - (void)applicationDidChangeScreenParameters:(NSNotification *) notification
 {
+    _GLFWwindow* window;
+
+    for (window = _glfw.windowListHead;  window;  window = window->next)
+    {
+        if (window->context.client != GLFW_NO_API)
+            [window->context.nsgl.object update];
+    }
+
     _glfwPollMonitorsNS();
 }
 

src/internal.h

@@ -303,6 +303,9 @@ struct _GLFWctxconfig
     int           robustness;
     int           release;
     _GLFWwindow*  share;
+    struct {
+        GLFWbool  offline;
+    } nsgl;
 };
 
 /*! @brief Framebuffer configuration.

src/nsgl_context.m

@@ -160,6 +160,18 @@ GLFWbool _glfwCreateContextNSGL(_GLFWwindow* window,
     ADD_ATTR(NSOpenGLPFAAccelerated);
     ADD_ATTR(NSOpenGLPFAClosestPolicy);
 
+    if (ctxconfig->nsgl.offline)
+    {
+        ADD_ATTR(NSOpenGLPFAAllowOfflineRenderers);
+        // NOTE: This replaces the NSSupportsAutomaticGraphicsSwitching key in
+        //       Info.plist for unbundled applications
+        // HACK: This assumes that NSOpenGLPixelFormat will remain
+        //       a straightforward wrapper of its CGL counterpart
+#if MAC_OS_X_VERSION_MAX_ALLOWED >= 100800
+        ADD_ATTR(kCGLPFASupportsAutomaticGraphicsSwitching);
+#endif /*MAC_OS_X_VERSION_MAX_ALLOWED*/
+    }
+
 #if MAC_OS_X_VERSION_MAX_ALLOWED >= 101000
     if (ctxconfig->major >= 4)
     {

src/window.c

@@ -345,6 +345,9 @@ GLFWAPI void glfwWindowHint(int hint, int value)
         case GLFW_COCOA_FRAME_AUTOSAVE:
             _glfw.hints.window.ns.frame = value ? GLFW_TRUE : GLFW_FALSE;
             break;
+        case GLFW_COCOA_GRAPHICS_SWITCHING:
+            _glfw.hints.context.nsgl.offline = value ? GLFW_TRUE : GLFW_FALSE;
+            break;
         case GLFW_CENTER_CURSOR:
             _glfw.hints.window.centerCursor = value ? GLFW_TRUE : GLFW_FALSE;
             break;