macOS: Implement background blurring

Uses a private API that allows us to control the amount of blurring.
While using a private API is obviously not ideal, it is used by both
iTerm.app and Apple's own Terminal.app, so hopefully it should stick
around. Fixes #6135

glfw/cocoa_platform.h

@@ -139,6 +139,7 @@ typedef struct _GLFWwindowNS
     int             width, height;
     int             fbWidth, fbHeight;
     float           xscale, yscale;
+    int             blur_radius;
 
     // The total sum of the distances the cursor has been warped
     // since the last cursor motion event was processed

glfw/cocoa_window.m

@@ -36,6 +36,8 @@
 #include <string.h>
 
 
+GLFWAPI int glfwCocoaSetBackgroundBlur(GLFWwindow *w, int radius);
+
 static const char*
 polymorphic_string_as_utf8(id string) {
     if (string == nil) return "(nil)";
@@ -1835,6 +1837,7 @@ static bool createNativeWindow(_GLFWwindow* window,
 
     _glfwPlatformGetWindowSize(window, &window->ns.width, &window->ns.height);
     _glfwPlatformGetFramebufferSize(window, &window->ns.fbWidth, &window->ns.fbHeight);
+    if (wndconfig->ns.blur_radius > 0) glfwCocoaSetBackgroundBlur((GLFWwindow*)window, wndconfig->ns.blur_radius);
 
     return true;
 }
@@ -2969,6 +2972,18 @@ GLFWAPI void glfwCocoaRequestRenderFrame(GLFWwindow *w, GLFWcocoarenderframefun
     requestRenderFrame((_GLFWwindow*)w, callback);
 }
 
+GLFWAPI int glfwCocoaSetBackgroundBlur(GLFWwindow *w, int radius) {
+    _GLFWwindow* window = (_GLFWwindow*)w;
+    int orig = window->ns.blur_radius;
+    if (radius > -1 && radius != window->ns.blur_radius) {
+        extern OSStatus CGSSetWindowBackgroundBlurRadius(void* connection, NSInteger windowNumber, int radius);
+        extern void* CGSDefaultConnectionForThread(void);
+        CGSSetWindowBackgroundBlurRadius(CGSDefaultConnectionForThread(), [window->ns.object windowNumber], radius);
+        window->ns.blur_radius = radius;
+    }
+    return orig;
+}
+
 GLFWAPI int glfwGetCurrentSystemColorTheme(void) {
     int theme_type = 0;
     NSAppearance *changedAppearance = NSApp.effectiveAppearance;

glfw/glfw.py

@@ -249,6 +249,7 @@ def generate_wrappers(glfw_header: str) -> None:
     GLFWapplicationwillfinishlaunchingfun glfwSetApplicationWillFinishLaunching(GLFWapplicationwillfinishlaunchingfun callback)
     uint32_t glfwGetCocoaKeyEquivalent(uint32_t glfw_key, int glfw_mods, int* cocoa_mods)
     void glfwCocoaRequestRenderFrame(GLFWwindow *w, GLFWcocoarenderframefun callback)
+    int glfwCocoaSetBackgroundBlur(GLFWwindow *w, int blur_radius)
     void* glfwGetX11Display(void)
     int32_t glfwGetX11Window(GLFWwindow* window)
     void glfwSetPrimarySelectionString(GLFWwindow* window, const char* string)

glfw/glfw3.h

@@ -1034,6 +1034,10 @@ typedef enum {
     SRGB_COLORSPACE = 1,
     DISPLAY_P3_COLORSPACE = 2,
 } GlfwCocoaColorSpaces;
+/*! @brief macOS specific
+ *  [window hint](@ref GLFW_COCOA_BLUR_RADIUS_hint).
+ */
+#define GLFW_COCOA_BLUR_RADIUS 0x00023005
 
 /*! @brief X11 specific
  *  [window hint](@ref GLFW_X11_CLASS_NAME_hint).

glfw/internal.h

@@ -313,6 +313,7 @@ struct _GLFWwndconfig
     struct {
         bool      retina;
         int       color_space;
+        int       blur_radius;
         char      frameName[256];
     } ns;
     struct {

glfw/window.c

@@ -334,6 +334,8 @@ void glfwDefaultWindowHints(void)
     _glfw.hints.window.ns.retina = true;
     // use the default colorspace assigned by the system
     _glfw.hints.window.ns.color_space = 0;
+    // no blur
+    _glfw.hints.window.ns.blur_radius = 0;
 }
 
 GLFWAPI void glfwWindowHint(int hint, int value)
@@ -417,6 +419,9 @@ GLFWAPI void glfwWindowHint(int hint, int value)
         case GLFW_COCOA_COLOR_SPACE:
             _glfw.hints.window.ns.color_space = value;
             return;
+        case GLFW_COCOA_BLUR_RADIUS:
+            _glfw.hints.window.ns.blur_radius = value;
+            return;
         case GLFW_COCOA_GRAPHICS_SWITCHING:
             _glfw.hints.context.nsgl.offline = value ? true : false;
             return;

kitty/glfw-wrapper.c

@@ -443,6 +443,9 @@ load_glfw(const char* path) {
     *(void **) (&glfwCocoaRequestRenderFrame_impl) = dlsym(handle, "glfwCocoaRequestRenderFrame");
     if (glfwCocoaRequestRenderFrame_impl == NULL) dlerror(); // clear error indicator
 
+    *(void **) (&glfwCocoaSetBackgroundBlur_impl) = dlsym(handle, "glfwCocoaSetBackgroundBlur");
+    if (glfwCocoaSetBackgroundBlur_impl == NULL) dlerror(); // clear error indicator
+
     *(void **) (&glfwGetX11Display_impl) = dlsym(handle, "glfwGetX11Display");
     if (glfwGetX11Display_impl == NULL) dlerror(); // clear error indicator
 

kitty/glfw-wrapper.h

@@ -772,6 +772,10 @@ typedef enum {
     SRGB_COLORSPACE = 1,
     DISPLAY_P3_COLORSPACE = 2,
 } GlfwCocoaColorSpaces;
+/*! @brief macOS specific
+ *  [window hint](@ref GLFW_COCOA_BLUR_RADIUS_hint).
+ */
+#define GLFW_COCOA_BLUR_RADIUS 0x00023005
 
 /*! @brief X11 specific
  *  [window hint](@ref GLFW_X11_CLASS_NAME_hint).
@@ -2216,6 +2220,10 @@ typedef void (*glfwCocoaRequestRenderFrame_func)(GLFWwindow*, GLFWcocoarenderfra
 GFW_EXTERN glfwCocoaRequestRenderFrame_func glfwCocoaRequestRenderFrame_impl;
 #define glfwCocoaRequestRenderFrame glfwCocoaRequestRenderFrame_impl
 
+typedef int (*glfwCocoaSetBackgroundBlur_func)(GLFWwindow*, int);
+GFW_EXTERN glfwCocoaSetBackgroundBlur_func glfwCocoaSetBackgroundBlur_impl;
+#define glfwCocoaSetBackgroundBlur glfwCocoaSetBackgroundBlur_impl
+
 typedef void* (*glfwGetX11Display_func)(void);
 GFW_EXTERN glfwGetX11Display_func glfwGetX11Display_impl;
 #define glfwGetX11Display glfwGetX11Display_impl

kitty/glfw.c

@@ -902,6 +902,11 @@ create_os_window(PyObject UNUSED *self, PyObject *args, PyObject *kw) {
 
 #ifdef __APPLE__
     glfwWindowHint(GLFW_COCOA_COLOR_SPACE, OPT(macos_colorspace));
+    if (OPT(background_blur) > 0 && OPT(background_opacity) < 1.f) {
+        glfwWindowHint(GLFW_COCOA_BLUR_RADIUS, MIN(OPT(background_blur), 128));
+    } else {
+        glfwWindowHint(GLFW_COCOA_BLUR_RADIUS, 0);
+    }
 #else
     glfwWindowHintString(GLFW_X11_INSTANCE_NAME, wm_class_name);
     glfwWindowHintString(GLFW_X11_CLASS_NAME, wm_class_class);
@@ -1081,6 +1086,17 @@ os_window_update_size_increments(OSWindow *window) {
     }
 }
 
+void
+update_background_blur(OSWindow *os_window) {
+#ifdef __APPLE__
+    int new_blur_radius = 0;
+    if (os_window->background_opacity < 1.f && OPT(background_blur) > -1) new_blur_radius = OPT(background_blur);
+    glfwCocoaSetBackgroundBlur(os_window->handle, new_blur_radius);
+#else
+    (void)os_window;
+#endif
+}
+
 #ifdef __APPLE__
 static bool
 window_in_same_cocoa_workspace(void *w, size_t *source_workspaces, size_t source_workspace_count) {

kitty/options/definition.py

@@ -1371,6 +1371,17 @@ config.
 '''
     )
 
+opt('background_blur', '0', option_type='int', ctype='int',
+    long_text='''
+Set to a positive value to enable background blur (blurring of the visuals
+behind a transparent window) on platforms that support it. Only takes effect
+when :opt:`background_opacity` is less than one. On macOS, this will also
+control the :italic:`blur radius` (amount of blurring). Setting it to too high
+a value will cause severe performance issues and/or rendering artifacts.
+Usually, values up to 64 work well. Note that this might cause performance issues,
+depending on how the platform implements it, so use with care.
+''')
+
 opt('background_image', 'none',
     option_type='config_or_absolute_path', ctype='!background_image',
     long_text='Path to a background image. Must be in PNG format.'

kitty/options/parse.py

@@ -65,6 +65,9 @@ class Parser:
     def background(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['background'] = to_color(val)
 
+    def background_blur(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
+        ans['background_blur'] = int(val)
+
     def background_image(self, val: str, ans: typing.Dict[str, typing.Any]) -> None:
         ans['background_image'] = config_or_absolute_path(val)
 

kitty/options/to-c-generated.h

@@ -733,6 +733,19 @@ convert_from_opts_background_opacity(PyObject *py_opts, Options *opts) {
     Py_DECREF(ret);
 }
 
+static void
+convert_from_python_background_blur(PyObject *val, Options *opts) {
+    opts->background_blur = PyLong_AsLong(val);
+}
+
+static void
+convert_from_opts_background_blur(PyObject *py_opts, Options *opts) {
+    PyObject *ret = PyObject_GetAttrString(py_opts, "background_blur");
+    if (ret == NULL) return;
+    convert_from_python_background_blur(ret, opts);
+    Py_DECREF(ret);
+}
+
 static void
 convert_from_python_background_image(PyObject *val, Options *opts) {
     background_image(val, opts);
@@ -1159,6 +1172,8 @@ convert_opts_from_python_opts(PyObject *py_opts, Options *opts) {
     if (PyErr_Occurred()) return false;
     convert_from_opts_background_opacity(py_opts, opts);
     if (PyErr_Occurred()) return false;
+    convert_from_opts_background_blur(py_opts, opts);
+    if (PyErr_Occurred()) return false;
     convert_from_opts_background_image(py_opts, opts);
     if (PyErr_Occurred()) return false;
     convert_from_opts_background_image_layout(py_opts, opts);

kitty/options/types.py

@@ -61,6 +61,7 @@ option_names = (  # {{{
  'allow_hyperlinks',
  'allow_remote_control',
  'background',
+ 'background_blur',
  'background_image',
  'background_image_layout',
  'background_image_linear',
@@ -480,6 +481,7 @@ class Options:
     allow_hyperlinks: int = 1
     allow_remote_control: choices_for_allow_remote_control = 'no'
     background: Color = Color(0, 0, 0)
+    background_blur: int = 0
     background_image: typing.Optional[str] = None
     background_image_layout: choices_for_background_image_layout = 'tiled'
     background_image_linear: bool = False
@@ -511,7 +513,7 @@ class Options:
     cursor_underline_thickness: float = 2.0
     default_pointer_shape: choices_for_default_pointer_shape = 'beam'
     detect_urls: bool = True
-    dim_opacity: float = 0.75
+    dim_opacity: float = 0.4
     disable_ligatures: int = 0
     draw_minimal_borders: bool = True
     dynamic_background_opacity: bool = False

kitty/state.c

@@ -1093,6 +1093,7 @@ PYWRAP0(apply_options_update) {
         get_platform_dependent_config_values(os_window->handle);
         os_window->background_opacity = OPT(background_opacity);
         os_window->is_damaged = true;
+        update_background_blur(os_window);
         for (size_t t = 0; t < os_window->num_tabs; t++) {
             Tab *tab = os_window->tabs + t;
             for (size_t w = 0; w < tab->num_windows; w++) {

kitty/state.h

@@ -89,6 +89,7 @@ typedef struct {
         float val; AdjustmentUnit unit;
     } underline_position, underline_thickness, strikethrough_position, strikethrough_thickness, cell_width, cell_height, baseline;
     bool show_hyperlink_targets;
+    int background_blur;
 } Options;
 
 typedef struct WindowLogoRenderData {
@@ -365,3 +366,4 @@ void update_ime_position(Window* w, Screen *screen);
 bool update_ime_position_for_window(id_type window_id, bool force, int update_focus);
 void set_ignore_os_keyboard_processing(bool enabled);
 void update_menu_bar_title(PyObject *title UNUSED);
+void update_background_blur(OSWindow *);