Add window blur hint/attribute

This adds very basic support for a new GLFW_BLURRED window
hint/attribute, and support in the X11 and null platforms. It is
intended to get feedback on whether this is the right API for this
feature, before diving into the other per-platform
implementations/stubs.

include/GLFW/glfw3.h

@@ -927,6 +927,13 @@ extern "C" {
  */
 #define GLFW_MOUSE_PASSTHROUGH      0x0002000D
 
+/*! @brief Blur behind window hint and attribute
+ *
+ *  Blur behind [window hint](@ref GLFW_BLURRED_hint) or
+ *  [window attribute](@ref GLFW_BLURRED_attrib).
+ */
+#define GLFW_BLURRED                 0x0002000E
+
 /*! @brief Framebuffer bit depth hint.
  *
  *  Framebuffer bit depth [hint](@ref GLFW_RED_BITS).

src/internal.h

@@ -410,6 +410,7 @@ struct _GLFWwndconfig
     GLFWbool      focusOnShow;
     GLFWbool      mousePassthrough;
     GLFWbool      scaleToMonitor;
+    GLFWbool      blurred;
     struct {
         GLFWbool  retina;
         char      frameName[256];
@@ -531,6 +532,7 @@ struct _GLFWwindow
     GLFWbool            focusOnShow;
     GLFWbool            mousePassthrough;
     GLFWbool            shouldClose;
+    GLFWbool            blurred;
     void*               userPointer;
     GLFWbool            doublebuffer;
     GLFWvidmode         videoMode;
@@ -748,6 +750,7 @@ struct _GLFWplatform
     void (*getRequiredInstanceExtensions)(char**);
     int (*getPhysicalDevicePresentationSupport)(VkInstance,VkPhysicalDevice,uint32_t);
     VkResult (*createWindowSurface)(VkInstance,_GLFWwindow*,const VkAllocationCallbacks*,VkSurfaceKHR*);
+    void (*setWindowBlur)(_GLFWwindow*,GLFWbool);
 };
 
 // Library global data

src/null_init.c

@@ -112,6 +112,7 @@ GLFWbool _glfwConnectNull(int platformID, _GLFWplatform* platform)
         _glfwGetRequiredInstanceExtensionsNull,
         _glfwGetPhysicalDevicePresentationSupportNull,
         _glfwCreateWindowSurfaceNull,
+        _glfwSetWindowBlurNull,
     };
 
     *platform = null;

src/null_platform.h

@@ -51,6 +51,7 @@ typedef struct _GLFWwindowNull
     GLFWbool        floating;
     GLFWbool        transparent;
     float           opacity;
+    GLFWbool        blurred;
 } _GLFWwindowNull;
 
 // Null-specific per-monitor data
@@ -111,6 +112,7 @@ void _glfwSetWindowFloatingNull(_GLFWwindow* window, GLFWbool enabled);
 void _glfwSetWindowMousePassthroughNull(_GLFWwindow* window, GLFWbool enabled);
 float _glfwGetWindowOpacityNull(_GLFWwindow* window);
 void _glfwSetWindowOpacityNull(_GLFWwindow* window, float opacity);
+void _glfwSetWindowBlurNull(_GLFWwindow* window, GLFWbool enabled);
 void _glfwSetRawMouseMotionNull(_GLFWwindow *window, GLFWbool enabled);
 GLFWbool _glfwRawMouseMotionSupportedNull(void);
 void _glfwShowWindowNull(_GLFWwindow* window);

src/null_window.c

@@ -409,6 +409,11 @@ void _glfwSetWindowOpacityNull(_GLFWwindow* window, float opacity)
     window->null.opacity = opacity;
 }
 
+void _glfwSetWindowBlurNull(_GLFWwindow* window, GLFWbool enable)
+{
+    window->null.blurred = enable;
+}
+
 void _glfwSetRawMouseMotionNull(_GLFWwindow *window, GLFWbool enabled)
 {
 }

src/window.c

@@ -359,6 +359,9 @@ GLFWAPI void glfwWindowHint(int hint, int value)
         case GLFW_MOUSE_PASSTHROUGH:
             _glfw.hints.window.mousePassthrough = value ? GLFW_TRUE : GLFW_FALSE;
             return;
+        case GLFW_BLURRED:
+            _glfw.hints.window.blurred = value ? GLFW_TRUE : GLFW_FALSE;
+            return;
         case GLFW_CLIENT_API:
             _glfw.hints.context.client = value;
             return;
@@ -826,6 +829,8 @@ GLFWAPI int glfwGetWindowAttrib(GLFWwindow* handle, int attrib)
             return window->focusOnShow;
         case GLFW_MOUSE_PASSTHROUGH:
             return window->mousePassthrough;
+        case GLFW_BLURRED:
+            return window->blurred;
         case GLFW_TRANSPARENT_FRAMEBUFFER:
             return _glfw.platform.framebufferTransparent(window);
         case GLFW_RESIZABLE:
@@ -907,6 +912,11 @@ GLFWAPI void glfwSetWindowAttrib(GLFWwindow* handle, int attrib, int value)
             window->mousePassthrough = value;
             _glfw.platform.setWindowMousePassthrough(window, value);
             return;
+
+        case GLFW_BLURRED:
+            window->blurred = value;
+            _glfw.platform.setWindowBlur(window, value);
+            return;
     }
 
     _glfwInputError(GLFW_INVALID_ENUM, "Invalid window attribute 0x%08X", attrib);

src/x11_init.c

@@ -972,6 +972,8 @@ static GLFWbool initExtensions(void)
         XInternAtom(_glfw.x11.display, "_NET_WM_WINDOW_OPACITY", False);
     _glfw.x11.MOTIF_WM_HINTS =
         XInternAtom(_glfw.x11.display, "_MOTIF_WM_HINTS", False);
+    _glfw.x11.KDE_NET_WM_BLUR_BEHIND_REGION =
+        XInternAtom(_glfw.x11.display, "_KDE_NET_WM_BLUR_BEHIND_REGION", False);
 
     // The compositing manager selection name contains the screen number
     {
@@ -1243,6 +1245,7 @@ GLFWbool _glfwConnectX11(int platformID, _GLFWplatform* platform)
         _glfwGetRequiredInstanceExtensionsX11,
         _glfwGetPhysicalDevicePresentationSupportX11,
         _glfwCreateWindowSurfaceX11,
+        _glfwSetWindowBlurX11,
     };
 
     // HACK: If the application has left the locale as "C" then both wide

src/x11_platform.h

@@ -614,6 +614,7 @@ typedef struct _GLFWlibraryX11
     Atom            NET_FRAME_EXTENTS;
     Atom            NET_REQUEST_FRAME_EXTENTS;
     Atom            MOTIF_WM_HINTS;
+    Atom            KDE_NET_WM_BLUR_BEHIND_REGION;
 
     // Xdnd (drag and drop) atoms
     Atom            XdndAware;
@@ -933,6 +934,7 @@ void _glfwSetWindowFloatingX11(_GLFWwindow* window, GLFWbool enabled);
 float _glfwGetWindowOpacityX11(_GLFWwindow* window);
 void _glfwSetWindowOpacityX11(_GLFWwindow* window, float opacity);
 void _glfwSetWindowMousePassthroughX11(_GLFWwindow* window, GLFWbool enabled);
+void _glfwSetWindowBlurX11(_GLFWwindow* window, GLFWbool enabled);
 
 void _glfwSetRawMouseMotionX11(_GLFWwindow *window, GLFWbool enabled);
 GLFWbool _glfwRawMouseMotionSupportedX11(void);

src/x11_window.c

@@ -604,6 +604,9 @@ static GLFWbool createNativeWindow(_GLFWwindow* window,
     if (!wndconfig->decorated)
         _glfwSetWindowDecoratedX11(window, GLFW_FALSE);
 
+    if (wndconfig->blurred)
+        _glfwSetWindowBlurX11(window, GLFW_TRUE);
+
     if (_glfw.x11.NET_WM_STATE && !window->monitor)
     {
         Atom states[3];
@@ -2699,6 +2702,17 @@ void _glfwSetWindowOpacityX11(_GLFWwindow* window, float opacity)
                     PropModeReplace, (unsigned char*) &value, 1);
 }
 
+void _glfwSetWindowBlurX11(_GLFWwindow* window, GLFWbool enable)
+{
+    if (enable)
+        XChangeProperty(_glfw.x11.display, window->x11.handle,
+                        _glfw.x11.KDE_NET_WM_BLUR_BEHIND_REGION, XA_CARDINAL, 32,
+                        PropModeReplace, NULL, 0);
+    else
+        XDeleteProperty(_glfw.x11.display, window->x11.handle,
+                        _glfw.x11.KDE_NET_WM_BLUR_BEHIND_REGION);
+}
+
 void _glfwSetRawMouseMotionX11(_GLFWwindow *window, GLFWbool enabled)
 {
     if (!_glfw.x11.xi.available)

tests/window.c

@@ -406,6 +406,10 @@ int main(int argc, char** argv)
             if (nk_checkbox_label(nk, "Auto Iconify", &auto_iconify))
                 glfwSetWindowAttrib(window, GLFW_AUTO_ICONIFY, auto_iconify);
 
+            int blurred = glfwGetWindowAttrib(window, GLFW_BLURRED);
+            if (nk_checkbox_label(nk, "Blur", &blurred))
+                glfwSetWindowAttrib(window, GLFW_BLURRED, blurred);
+
             nk_value_bool(nk, "Focused", glfwGetWindowAttrib(window, GLFW_FOCUSED));
             nk_value_bool(nk, "Hovered", glfwGetWindowAttrib(window, GLFW_HOVERED));
             nk_value_bool(nk, "Visible", glfwGetWindowAttrib(window, GLFW_VISIBLE));