Add support for mouse input transparency

This adds the GLFW_MOUSE_PASSTHROUGH window hint and attribute for
controlling whether mouse input passes through the window to whatever
window is behind it.

Fixes #1236.
Closes #1568.

include/GLFW/glfw3.h

@@ -895,6 +895,13 @@ extern "C" {
  */
 #define GLFW_FOCUS_ON_SHOW          0x0002000C
 
+/*! @brief Forward mouse input to window behind.
+ *
+ *  Mouse input forwarding[window hint](@ref GLFW_MOUSE_PASSTHROUGH_hint) or
+ *  [window attribute](@ref GLFW_MOUSE_PASSTHROUGH_attrib).
+ */
+#define GLFW_MOUSE_PASSTHROUGH      0x0002000D
+
 /*! @brief Framebuffer bit depth hint.
  *
  *  Framebuffer bit depth [hint](@ref GLFW_RED_BITS).
@@ -3656,6 +3663,7 @@ GLFWAPI int glfwGetWindowAttrib(GLFWwindow* window, int attrib);
  *  [GLFW_FLOATING](@ref GLFW_FLOATING_attrib),
  *  [GLFW_AUTO_ICONIFY](@ref GLFW_AUTO_ICONIFY_attrib) and
  *  [GLFW_FOCUS_ON_SHOW](@ref GLFW_FOCUS_ON_SHOW_attrib).
+ *  [GLFW_MOUSE_PASSTHROUGH](@ref GLFW_MOUSE_PASSTHROUGH_attrib)
  *
  *  Some of these attributes are ignored for full screen windows.  The new
  *  value will take effect if the window is later made windowed.

src/cocoa_window.m

@@ -1371,6 +1371,14 @@ void _glfwPlatformSetWindowFloating(_GLFWwindow* window, GLFWbool enabled)
     } // autoreleasepool
 }
 
+void _glfwPlatformSetWindowMousePassthrough(_GLFWwindow* window, GLFWbool enabled)
+{
+    window->mousePassthrough = enabled;
+    @autoreleasepool {
+    [window->ns.object setIgnoresMouseEvents:enabled];
+    }
+}
+
 float _glfwPlatformGetWindowOpacity(_GLFWwindow* window)
 {
     @autoreleasepool {

src/internal.h

@@ -270,6 +270,7 @@ struct _GLFWwndconfig
     GLFWbool      maximized;
     GLFWbool      centerCursor;
     GLFWbool      focusOnShow;
+    GLFWbool      mousePassthrough;
     GLFWbool      scaleToMonitor;
     struct {
         GLFWbool  retina;
@@ -380,6 +381,7 @@ struct _GLFWwindow
     GLFWbool            autoIconify;
     GLFWbool            floating;
     GLFWbool            focusOnShow;
+    GLFWbool            mousePassthrough;
     GLFWbool            shouldClose;
     void*               userPointer;
     GLFWvidmode         videoMode;
@@ -678,6 +680,7 @@ float _glfwPlatformGetWindowOpacity(_GLFWwindow* window);
 void _glfwPlatformSetWindowResizable(_GLFWwindow* window, GLFWbool enabled);
 void _glfwPlatformSetWindowDecorated(_GLFWwindow* window, GLFWbool enabled);
 void _glfwPlatformSetWindowFloating(_GLFWwindow* window, GLFWbool enabled);
+void _glfwPlatformSetWindowMousePassthrough(_GLFWwindow* window, GLFWbool enabled);
 void _glfwPlatformSetWindowOpacity(_GLFWwindow* window, float opacity);
 
 void _glfwPlatformPollEvents(void);

src/null_window.c

@@ -362,6 +362,10 @@ void _glfwPlatformSetWindowFloating(_GLFWwindow* window, GLFWbool enabled)
     window->null.floating = enabled;
 }
 
+void _glfwPlatformSetWindowMousePassthrough(_GLFWwindow* window, GLFWbool enabled)
+{
+}
+
 float _glfwPlatformGetWindowOpacity(_GLFWwindow* window)
 {
     return window->null.opacity;

src/win32_window.c

@@ -1201,6 +1201,13 @@ static LRESULT CALLBACK windowProc(HWND hWnd, UINT uMsg,
             DragFinish(drop);
             return 0;
         }
+
+        case WM_NCHITTEST:
+        {
+            if (window->mousePassthrough)
+                return HTTRANSPARENT;
+            break;
+        }
     }
 
     return DefWindowProcW(hWnd, uMsg, wParam, lParam);
@@ -1854,6 +1861,11 @@ void _glfwPlatformSetWindowFloating(_GLFWwindow* window, GLFWbool enabled)
                  SWP_NOACTIVATE | SWP_NOMOVE | SWP_NOSIZE);
 }
 
+void _glfwPlatformSetWindowMousePassthrough(_GLFWwindow* window, GLFWbool enabled)
+{
+    window->mousePassthrough = enabled;
+}
+
 float _glfwPlatformGetWindowOpacity(_GLFWwindow* window)
 {
     BYTE alpha;

src/window.c

@@ -243,6 +243,8 @@ GLFWAPI GLFWwindow* glfwCreateWindow(int width, int height,
         }
     }
 
+    _glfwPlatformSetWindowMousePassthrough(window, wndconfig.mousePassthrough);
+
     return (GLFWwindow*) window;
 }
 
@@ -378,6 +380,9 @@ GLFWAPI void glfwWindowHint(int hint, int value)
         case GLFW_FOCUS_ON_SHOW:
             _glfw.hints.window.focusOnShow = value ? GLFW_TRUE : GLFW_FALSE;
             return;
+        case GLFW_MOUSE_PASSTHROUGH:
+            _glfw.hints.window.mousePassthrough = value ? GLFW_TRUE : GLFW_FALSE;
+            return;
         case GLFW_CLIENT_API:
             _glfw.hints.context.client = value;
             return;
@@ -822,6 +827,8 @@ GLFWAPI int glfwGetWindowAttrib(GLFWwindow* handle, int attrib)
             return _glfwPlatformWindowHovered(window);
         case GLFW_FOCUS_ON_SHOW:
             return window->focusOnShow;
+        case GLFW_MOUSE_PASSTHROUGH:
+            return window->mousePassthrough;
         case GLFW_TRANSPARENT_FRAMEBUFFER:
             return _glfwPlatformFramebufferTransparent(window);
         case GLFW_RESIZABLE:
@@ -900,6 +907,8 @@ GLFWAPI void glfwSetWindowAttrib(GLFWwindow* handle, int attrib, int value)
     }
     else if (attrib == GLFW_FOCUS_ON_SHOW)
         window->focusOnShow = value;
+    else if (attrib == GLFW_MOUSE_PASSTHROUGH)
+        _glfwPlatformSetWindowMousePassthrough(window, value);
     else
         _glfwInputError(GLFW_INVALID_ENUM, "Invalid window attribute 0x%08X", attrib);
 }

src/wl_window.c

@@ -1127,6 +1127,23 @@ void _glfwPlatformSetWindowFloating(_GLFWwindow* window, GLFWbool enabled)
                     "Wayland: Window attribute setting not implemented yet");
 }
 
+void _glfwPlatformSetWindowMousePassthrough(_GLFWwindow* window, GLFWbool enabled)
+{
+    if (enabled == window->mousePassthrough)
+        return;
+
+    if (enabled)
+    {
+        struct wl_region* region = wl_compositor_create_region(_glfw.wl.compositor);
+        wl_surface_set_input_region(window->wl.surface, region);
+        wl_region_destroy(region);
+    }
+    else
+        wl_surface_set_input_region(window->wl.surface, 0);
+    wl_surface_commit(window->wl.surface);
+    window->mousePassthrough = enabled;
+}
+
 float _glfwPlatformGetWindowOpacity(_GLFWwindow* window)
 {
     return 1.f;

src/x11_init.c

@@ -851,6 +851,33 @@ static GLFWbool initExtensions(void)
         }
     }
 
+#if defined(__CYGWIN__)
+    _glfw.x11.xshape.handle = _glfw_dlopen("libXext-6.so");
+#else
+    _glfw.x11.xshape.handle = _glfw_dlopen("libXext.so.6");
+#endif
+    if (_glfw.x11.xshape.handle)
+    {
+        _glfw.x11.xshape.QueryExtension = (PFN_XShapeQueryExtension)
+            _glfw_dlsym(_glfw.x11.xshape.handle, "XShapeQueryExtension");
+        _glfw.x11.xshape.ShapeCombineRegion = (PFN_XShapeCombineRegion)
+            _glfw_dlsym(_glfw.x11.xshape.handle, "XShapeCombineRegion");
+        _glfw.x11.xshape.QueryVersion = (PFN_XShapeQueryVersion)
+            _glfw_dlsym(_glfw.x11.xshape.handle, "XShapeQueryVersion");
+
+        if (XShapeQueryExtension(_glfw.x11.display,
+            &_glfw.x11.xshape.errorBase,
+            &_glfw.x11.xshape.eventBase))
+        {
+            if (XShapeQueryVersion(_glfw.x11.display,
+                &_glfw.x11.xshape.major,
+                &_glfw.x11.xshape.minor))
+            {
+                _glfw.x11.xshape.available = GLFW_TRUE;
+            }
+        }
+    }
+
     // Update the key code LUT
     // FIXME: We should listen to XkbMapNotify events to track changes to
     // the keyboard mapping.
@@ -1122,6 +1149,8 @@ int _glfwPlatformInit(void)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XCreateFontCursor");
     _glfw.x11.xlib.CreateIC = (PFN_XCreateIC)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XCreateIC");
+    _glfw.x11.xlib.CreateRegion = (PFN_XCreateRegion)
+        _glfw_dlsym(_glfw.x11.xlib.handle, "XCreateRegion");
     _glfw.x11.xlib.CreateWindow = (PFN_XCreateWindow)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XCreateWindow");
     _glfw.x11.xlib.DefineCursor = (PFN_XDefineCursor)
@@ -1132,6 +1161,8 @@ int _glfwPlatformInit(void)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XDeleteProperty");
     _glfw.x11.xlib.DestroyIC = (PFN_XDestroyIC)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XDestroyIC");
+    _glfw.x11.xlib.DestroyRegion = (PFN_XDestroyRegion)
+        _glfw_dlsym(_glfw.x11.xlib.handle, "XDestroyRegion");
     _glfw.x11.xlib.DestroyWindow = (PFN_XDestroyWindow)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XDestroyWindow");
     _glfw.x11.xlib.DisplayKeycodes = (PFN_XDisplayKeycodes)
@@ -1254,6 +1285,8 @@ int _glfwPlatformInit(void)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XUndefineCursor");
     _glfw.x11.xlib.UngrabPointer = (PFN_XUngrabPointer)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XUngrabPointer");
+    _glfw.x11.xlib.UnionRectWithRegion = (PFN_XUnionRectWithRegion)
+        _glfw_dlsym(_glfw.x11.xlib.handle, "XUnionRectWithRegion");
     _glfw.x11.xlib.UnmapWindow = (PFN_XUnmapWindow)
         _glfw_dlsym(_glfw.x11.xlib.handle, "XUnmapWindow");
     _glfw.x11.xlib.UnsetICFocus = (PFN_XUnsetICFocus)

src/x11_platform.h

@@ -61,11 +61,13 @@ typedef int (* PFN_XConvertSelection)(Display*,Atom,Atom,Atom,Window,Time);
 typedef Colormap (* PFN_XCreateColormap)(Display*,Window,Visual*,int);
 typedef Cursor (* PFN_XCreateFontCursor)(Display*,unsigned int);
 typedef XIC (* PFN_XCreateIC)(XIM,...);
+typedef Region (* PFN_XCreateRegion)(void);
 typedef Window (* PFN_XCreateWindow)(Display*,Window,int,int,unsigned int,unsigned int,unsigned int,int,unsigned int,Visual*,unsigned long,XSetWindowAttributes*);
 typedef int (* PFN_XDefineCursor)(Display*,Window,Cursor);
 typedef int (* PFN_XDeleteContext)(Display*,XID,XContext);
 typedef int (* PFN_XDeleteProperty)(Display*,Window,Atom);
 typedef void (* PFN_XDestroyIC)(XIC);
+typedef int (* PFN_XDestroyRegion)(Region);
 typedef int (* PFN_XDestroyWindow)(Display*,Window);
 typedef int (* PFN_XDisplayKeycodes)(Display*,int*,int*);
 typedef int (* PFN_XEventsQueued)(Display*,int);
@@ -127,6 +129,7 @@ typedef int (* PFN_XSync)(Display*,Bool);
 typedef Bool (* PFN_XTranslateCoordinates)(Display*,Window,Window,int,int,int*,int*,Window*);
 typedef int (* PFN_XUndefineCursor)(Display*,Window);
 typedef int (* PFN_XUngrabPointer)(Display*,Time);
+typedef int (* PFN_XUnionRectWithRegion)(XRectangle*,Region,Region);
 typedef int (* PFN_XUnmapWindow)(Display*,Window);
 typedef void (* PFN_XUnsetICFocus)(XIC);
 typedef VisualID (* PFN_XVisualIDFromVisual)(Visual*);
@@ -161,11 +164,13 @@ typedef void (* PFN_Xutf8SetWMProperties)(Display*,Window,const char*,const char
 #define XCreateColormap _glfw.x11.xlib.CreateColormap
 #define XCreateFontCursor _glfw.x11.xlib.CreateFontCursor
 #define XCreateIC _glfw.x11.xlib.CreateIC
+#define XCreateRegion _glfw.x11.xlib.CreateRegion
 #define XCreateWindow _glfw.x11.xlib.CreateWindow
 #define XDefineCursor _glfw.x11.xlib.DefineCursor
 #define XDeleteContext _glfw.x11.xlib.DeleteContext
 #define XDeleteProperty _glfw.x11.xlib.DeleteProperty
 #define XDestroyIC _glfw.x11.xlib.DestroyIC
+#define XDestroyRegion _glfw.x11.xlib.DestroyRegion
 #define XDestroyWindow _glfw.x11.xlib.DestroyWindow
 #define XDisplayKeycodes _glfw.x11.xlib.DisplayKeycodes
 #define XEventsQueued _glfw.x11.xlib.EventsQueued
@@ -227,6 +232,7 @@ typedef void (* PFN_Xutf8SetWMProperties)(Display*,Window,const char*,const char
 #define XTranslateCoordinates _glfw.x11.xlib.TranslateCoordinates
 #define XUndefineCursor _glfw.x11.xlib.UndefineCursor
 #define XUngrabPointer _glfw.x11.xlib.UngrabPointer
+#define XUnionRectWithRegion _glfw.x11.xlib.UnionRectWithRegion
 #define XUnmapWindow _glfw.x11.xlib.UnmapWindow
 #define XUnsetICFocus _glfw.x11.xlib.UnsetICFocus
 #define XVisualIDFromVisual _glfw.x11.xlib.VisualIDFromVisual
@@ -331,6 +337,13 @@ typedef XRenderPictFormat* (* PFN_XRenderFindVisualFormat)(Display*,Visual const
 #define XRenderQueryVersion _glfw.x11.xrender.QueryVersion
 #define XRenderFindVisualFormat _glfw.x11.xrender.FindVisualFormat
 
+typedef Bool (* PFN_XShapeQueryExtension)(Display*,int*,int*);
+typedef Status (* PFN_XShapeQueryVersion)(Display*dpy,int*,int*);
+typedef void (* PFN_XShapeCombineRegion)(Display*,Window,int,int,int,Region,int);
+#define XShapeQueryExtension _glfw.x11.xshape.QueryExtension
+#define XShapeQueryVersion _glfw.x11.xshape.QueryVersion
+#define XShapeCombineRegion _glfw.x11.xshape.ShapeCombineRegion
+
 typedef VkFlags VkXlibSurfaceCreateFlagsKHR;
 typedef VkFlags VkXcbSurfaceCreateFlagsKHR;
 
@@ -515,11 +528,13 @@ typedef struct _GLFWlibraryX11
         PFN_XCreateColormap CreateColormap;
         PFN_XCreateFontCursor CreateFontCursor;
         PFN_XCreateIC CreateIC;
+        PFN_XCreateRegion CreateRegion;
         PFN_XCreateWindow CreateWindow;
         PFN_XDefineCursor DefineCursor;
         PFN_XDeleteContext DeleteContext;
         PFN_XDeleteProperty DeleteProperty;
         PFN_XDestroyIC DestroyIC;
+        PFN_XDestroyRegion DestroyRegion;
         PFN_XDestroyWindow DestroyWindow;
         PFN_XDisplayKeycodes DisplayKeycodes;
         PFN_XEventsQueued EventsQueued;
@@ -581,6 +596,7 @@ typedef struct _GLFWlibraryX11
         PFN_XTranslateCoordinates TranslateCoordinates;
         PFN_XUndefineCursor UndefineCursor;
         PFN_XUngrabPointer UngrabPointer;
+        PFN_XUnionRectWithRegion UnionRectWithRegion;
         PFN_XUnmapWindow UnmapWindow;
         PFN_XUnsetICFocus UnsetICFocus;
         PFN_XVisualIDFromVisual VisualIDFromVisual;
@@ -720,6 +736,18 @@ typedef struct _GLFWlibraryX11
         PFN_XRenderFindVisualFormat FindVisualFormat;
     } xrender;
 
+    struct {
+        GLFWbool    available;
+        void*       handle;
+        int         major;
+        int         minor;
+        int         eventBase;
+        int         errorBase;
+        PFN_XShapeQueryExtension QueryExtension;
+        PFN_XShapeCombineRegion ShapeCombineRegion;
+        PFN_XShapeQueryVersion QueryVersion;
+    } xshape;
+
 } _GLFWlibraryX11;
 
 // X11-specific per-monitor data

src/x11_window.c

@@ -2702,6 +2702,32 @@ void _glfwPlatformSetWindowFloating(_GLFWwindow* window, GLFWbool enabled)
     XFlush(_glfw.x11.display);
 }
 
+void _glfwPlatformSetWindowMousePassthrough(_GLFWwindow* window, GLFWbool enabled)
+{
+    if (!_glfw.x11.xshape.available)
+        return;
+
+    if (enabled == window->mousePassthrough)
+        return;
+
+    int width = 0;
+    int height = 0;
+    if (!enabled)
+        _glfwPlatformGetWindowSize(window, &width, &height);
+
+    XRectangle rect;
+    rect.x = 0;
+    rect.y = 0;
+    rect.width = (unsigned short)width;
+    rect.height = (unsigned short)height;
+
+    Region region = XCreateRegion();
+    XUnionRectWithRegion(&rect, region, region);
+    XShapeCombineRegion(_glfw.x11.display, window->x11.handle, 2/*ShapeInput*/, 0, 0, region, 0/*ShapeSet*/);
+    XDestroyRegion(region);
+    window->mousePassthrough = enabled;
+}
+
 float _glfwPlatformGetWindowOpacity(_GLFWwindow* window)
 {
     float opacity = 1.f;