macOS: Respect the system setting for text insertion cursor blink time

This value can be changed with the following commands:

defaults write -g NSTextInsertionPointBlinkPeriodOff -float 500
defaults write -g NSTextInsertionPointBlinkPeriodOn -float 500

setup/extensions.json

@@ -186,6 +186,12 @@
         "sources": "calibre/devices/usbobserver/usbobserver.c",
         "ldflags": "-framework CoreServices -framework IOKit"
     },
+    {
+        "name": "cocoa",
+        "only": "osx",
+        "sources": "calibre/utils/cocoa.m calibre/utils/cocoa_wrapper.c",
+        "ldflags": "-framework Cocoa"
+    },
     {
         "name": "libusb",
         "only": "osx linux haiku",

src/calibre/constants.py

@@ -189,6 +189,7 @@ class Plugins(collections.Mapping):
             plugins.extend(['winutil', 'wpd', 'winfonts'])
         if isosx:
             plugins.append('usbobserver')
+            plugins.append('cocoa')
         if isfreebsd or ishaiku or islinux or isosx:
             plugins.append('libusb')
             plugins.append('libmtp')

src/calibre/gui2/__init__.py

@@ -894,6 +894,14 @@ class Application(QApplication):
             # Qt 5 bug: https://bugreports.qt-project.org/browse/QTBUG-41125
             self.aboutToQuit.connect(self.flush_clipboard)
 
+        if isosx:
+            cocoa, err = plugins['cocoa']
+            if err:
+                raise RuntimeError('Failed to load cocoa plugin with error: {}'.format(err))
+            cft = cocoa.cursor_blink_time()
+            if cft >= 0:
+                self.setCursorFlashTime(int(cft))
+
     def setup_ui_font(self):
         f = QFont(QApplication.font())
         q = (f.family(), f.pointSize())

src/calibre/utils/cocoa.m

@@ -0,0 +1,25 @@
+/*
+ * cocoa.m
+ * Copyright (C) 2019 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+
+#include <Cocoa/Cocoa.h>
+
+
+double
+cocoa_cursor_blink_time(void) {
+    NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
+    double on_period_ms = [defaults doubleForKey:@"NSTextInsertionPointBlinkPeriodOn"];
+    double off_period_ms = [defaults doubleForKey:@"NSTextInsertionPointBlinkPeriodOff"];
+    double period_ms = [defaults doubleForKey:@"NSTextInsertionPointBlinkPeriod"];
+    double max_value = 60 * 1000.0, ans = -1.0;
+    if (on_period_ms || off_period_ms) {
+        ans = on_period_ms + off_period_ms;
+    } else if (period_ms) {
+        ans = period_ms;
+    }
+    return ans > max_value ? 0.0 : ans;
+}

src/calibre/utils/cocoa_wrapper.c

@@ -0,0 +1,53 @@
+/*
+ * cocoa_wrapper.c
+ * Copyright (C) 2019 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+#include <Python.h>
+
+extern double cocoa_cursor_blink_time(void);
+
+static PyObject*
+cursor_blink_time(PyObject *self) {
+    (void)self;
+    double ans = cocoa_cursor_blink_time();
+    return PyFloat_FromDouble(ans);
+}
+
+static PyMethodDef module_methods[] = {
+    {"cursor_blink_time", (PyCFunction)cursor_blink_time, METH_NOARGS, ""},
+    {NULL, NULL, 0, NULL}        /* Sentinel */
+};
+
+
+#if PY_MAJOR_VERSION >= 3
+#define INITERROR return NULL
+#define INITMODULE PyModule_Create(&bzzdec_module)
+static struct PyModuleDef cocoa_module = {
+    /* m_base     */ PyModuleDef_HEAD_INIT,
+    /* m_name     */ "cocoa",
+    /* m_doc      */ "",
+    /* m_size     */ -1,
+    /* m_methods  */ module_methods,
+    /* m_slots    */ 0,
+    /* m_traverse */ 0,
+    /* m_clear    */ 0,
+    /* m_free     */ 0,
+};
+CALIBRE_MODINIT_FUNC PyInit_cocoa(void) {
+#else
+#define INITERROR return
+#define INITMODULE Py_InitModule3("cocoa", module_methods, "")
+CALIBRE_MODINIT_FUNC initcocoa(void) {
+#endif
+
+    PyObject *m = INITMODULE;
+    if (m == NULL) {
+        INITERROR;
+    }
+#if PY_MAJOR_VERSION >= 3
+    return m;
+#endif
+}