Observe changes in accessibility access continuously

Author: emreyolcu

DiscreteScroll.xcodeproj/project.pbxproj

@@ -249,14 +249,14 @@
 			buildSettings = {
 				CODE_SIGN_STYLE = Automatic;
 				COMBINE_HIDPI_IMAGES = YES;
-				CURRENT_PROJECT_VERSION = 2;
+				CURRENT_PROJECT_VERSION = 3;
 				INFOPLIST_FILE = DiscreteScroll/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/../Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 10.9;
-				MARKETING_VERSION = 1.0.1;
+				MARKETING_VERSION = 1.1.0;
 				PRODUCT_BUNDLE_IDENTIFIER = com.emreyolcu.DiscreteScroll;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 			};
@@ -267,14 +267,14 @@
 			buildSettings = {
 				CODE_SIGN_STYLE = Automatic;
 				COMBINE_HIDPI_IMAGES = YES;
-				CURRENT_PROJECT_VERSION = 2;
+				CURRENT_PROJECT_VERSION = 3;
 				INFOPLIST_FILE = DiscreteScroll/Info.plist;
 				LD_RUNPATH_SEARCH_PATHS = (
 					"$(inherited)",
 					"@executable_path/../Frameworks",
 				);
 				MACOSX_DEPLOYMENT_TARGET = 10.9;
-				MARKETING_VERSION = 1.0.1;
+				MARKETING_VERSION = 1.1.0;
 				PRODUCT_BUNDLE_IDENTIFIER = com.emreyolcu.DiscreteScroll;
 				PRODUCT_NAME = "$(TARGET_NAME)";
 			};

DiscreteScroll/main.c

@@ -3,9 +3,16 @@
 #define DEFAULT_LINES 3
 #define SIGN(x) (((x) > 0) - ((x) < 0))
 
+static const CFStringRef AX_NOTIFICATION = CFSTR("com.apple.accessibility.api");
+static bool TRUSTED;
+
+static CFMachPortRef TAP;
+static CFRunLoopSourceRef SOURCE;
+
 static int LINES;
 
-CGEventRef callback(CGEventTapProxy proxy, CGEventType type, CGEventRef event, void *userInfo)
+static CGEventRef tapCallback(CGEventTapProxy proxy,
+                              CGEventType type, CGEventRef event, void *userInfo)
 {
     if (CGEventGetIntegerValueField(event, kCGScrollWheelEventIsContinuous) == 0) {
         int delta = (int)CGEventGetIntegerValueField(event, kCGScrollWheelEventPointDeltaAxis1);
@@ -15,7 +22,7 @@ CGEventRef callback(CGEventTapProxy proxy, CGEventType type, CGEventRef event, v
     return event;
 }
 
-void displayNoticeAndExit(CFStringRef alertHeader)
+static void displayNoticeAndExit(CFStringRef alertHeader)
 {
     CFUserNotificationDisplayNotice(
         0, kCFUserNotificationCautionAlertLevel,
@@ -26,44 +33,74 @@ void displayNoticeAndExit(CFStringRef alertHeader)
     exit(EXIT_FAILURE);
 }
 
+static void notificationCallback(CFNotificationCenterRef center, void *observer,
+                                 CFNotificationName name, const void *object,
+                                 CFDictionaryRef userInfo)
+{
+    if (CFStringCompare(name, AX_NOTIFICATION, 0) == kCFCompareEqualTo) {
+        CFRunLoopRef runLoop = CFRunLoopGetCurrent();
+        CFRunLoopPerformBlock(
+            runLoop, kCFRunLoopDefaultMode, ^{
+                bool previouslyTrusted = TRUSTED;
+                if ((TRUSTED = AXIsProcessTrusted()) != previouslyTrusted) {
+                    CFRunLoopStop(runLoop);
+                    if (SOURCE && CFRunLoopContainsSource(runLoop, SOURCE, kCFRunLoopDefaultMode)) {
+                        CGEventTapEnable(TAP, TRUSTED);
+                        CFRunLoopRun();
+                    } else if (!TRUSTED) {
+                        CFRunLoopRun();
+                    }
+                }
+            }
+        );
+    }
+}
+
+static bool getIntPreference(CFStringRef key, int *valuePtr)
+{
+    CFNumberRef number = (CFNumberRef)CFPreferencesCopyAppValue(
+        key, kCFPreferencesCurrentApplication
+    );
+    bool got = false;
+    if (number) {
+        if (CFGetTypeID(number) == CFNumberGetTypeID())
+            got = CFNumberGetValue(number, kCFNumberIntType, valuePtr);
+        CFRelease(number);
+    }
+
+    return got;
+}
+
 int main(void)
 {
+    CFNotificationCenterAddObserver(
+        CFNotificationCenterGetDistributedCenter(), NULL,
+        notificationCallback, AX_NOTIFICATION, NULL,
+        CFNotificationSuspensionBehaviorDeliverImmediately
+    );
     CFDictionaryRef options = CFDictionaryCreate(
         kCFAllocatorDefault,
         (const void **)&kAXTrustedCheckOptionPrompt, (const void **)&kCFBooleanTrue, 1,
         &kCFTypeDictionaryKeyCallBacks, &kCFTypeDictionaryValueCallBacks
     );
-    bool trusted = AXIsProcessTrustedWithOptions(options);
+    TRUSTED = AXIsProcessTrustedWithOptions(options);
     CFRelease(options);
-    if (!trusted)
-        displayNoticeAndExit(
-            CFSTR("Restart DiscreteScroll after granting it access to accessibility features.")
-        );
+    if (!TRUSTED)
+        CFRunLoopRun();
 
-    CFNumberRef value = (CFNumberRef)CFPreferencesCopyAppValue(
-        CFSTR("lines"), kCFPreferencesCurrentApplication
-    );
-    bool got = false;
-    if (value) {
-        if (CFGetTypeID(value) == CFNumberGetTypeID())
-            got = CFNumberGetValue(value, kCFNumberIntType, &LINES);
-        CFRelease(value);
-    }
-    if (!got)
+    if (!getIntPreference(CFSTR("lines"), &LINES))
         LINES = DEFAULT_LINES;
 
-    CFMachPortRef tap = CGEventTapCreate(
+    TAP = CGEventTapCreate(
         kCGSessionEventTap, kCGHeadInsertEventTap, kCGEventTapOptionDefault,
-        CGEventMaskBit(kCGEventScrollWheel), callback, NULL
+        CGEventMaskBit(kCGEventScrollWheel), tapCallback, NULL
     );
-    if (!tap)
+    if (!TAP)
         displayNoticeAndExit(CFSTR("DiscreteScroll could not create an event tap."));
-    CFRunLoopSourceRef source = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, tap, 0);
-    if (!source)
+    SOURCE = CFMachPortCreateRunLoopSource(kCFAllocatorDefault, TAP, 0);
+    if (!SOURCE)
         displayNoticeAndExit(CFSTR("DiscreteScroll could not create a run loop source."));
-    CFRunLoopAddSource(CFRunLoopGetCurrent(), source, kCFRunLoopDefaultMode);
-    CFRelease(tap);
-    CFRelease(source);
+    CFRunLoopAddSource(CFRunLoopGetCurrent(), SOURCE, kCFRunLoopDefaultMode);
     CFRunLoopRun();
 
     return EXIT_SUCCESS;

README.md

@@ -14,16 +14,28 @@ As of May 2024, this application works on macOS versions 10.9–14.0.
 
 ### Installation
 
-You may download the binary [here](https://github.com/emreyolcu/discrete-scroll/releases/download/v1.0.1/DiscreteScroll.zip).
-
-It needs to be run each time you boot.
-If you want this to be automatic, do the following:
+You may download the binary [here](https://github.com/emreyolcu/discrete-scroll/releases/download/v1.1.0/DiscreteScroll.zip).
+DiscreteScroll requires access to accessibility features.
+Upon startup, if it does not have access, it will prompt you and wait.
+You do not need to restart the application
+after you grant it access to accessibility features.
+
+> [!CAUTION]
+> You may safely toggle accessibility access
+> for DiscreteScroll while it is running.
+> *However, you should not remove it from the list of trusted applications
+> while it is running without first unchecking the box next to its name.
+> Otherwise, your mouse might become unresponsive.*
+
+If you want the application to run automatically when you log in,
+do the following:
 
 1. On macOS 13.0 and later, go to `System Settings > General > Login Items`;
    otherwise, go to `System Preferences > Users & Groups > Login Items`.
 2. Add `DiscreteScroll` to the list.
 
-If you want to quit the application, do the following:
+If you want to quit the application, either run `killall DiscreteScroll`
+or do the following:
 
 1. Launch `Activity Monitor`.
 2. Search for `DiscreteScroll` and select it.
@@ -40,11 +52,22 @@ This number may even be negative, which inverts scrolling direction.
 defaults write com.emreyolcu.DiscreteScroll lines -int LINES
 ```
 
-If you set the key `lines` to some value other than an integer,
-the default value of 3 is used as a fallback.
+> [!WARNING]
+> If you set `lines` to some value other than an integer,
+> then the default value of 3 is used as a fallback.
 
 You should restart the application for the setting to take effect.
 
+### Uninstallation
+
+To uninstall DiscreteScroll, quit the application, move it to trash,
+and remove it from the lists for accessibility access and login items.
+You can remove any stored preferences by running the following:
+
+```
+defaults delete com.emreyolcu.DiscreteScroll
+```
+
 ### Potential problems
 
 Recent versions of macOS have made it difficult to run unsigned binaries.