Keep one macOS cursor density snapshot and retry failed captures

src/platform/macos.rs

@@ -37,6 +37,9 @@ use std::{
 
 mod cursor;
 
+#[cfg(test)]
+mod cursor_poll_tests;
+
 // macOS boolean_t is defined as `int` in <mach/boolean.h>
 type BooleanT = hbb_common::libc::c_int;
 
@@ -567,10 +570,10 @@ fn unsafe_get_cursor() -> ResultType<Option<u64>> {
         if seed == LATEST_SEED {
             return Ok(None);
         }
+        let c = get_cursor_id(seed.1)?;
         LATEST_SEED = seed;
+        Ok(Some(c.1))
     }
-    let c = get_cursor_id()?;
-    Ok(Some(c.1))
 }
 
 pub fn reset_input_cache() {
@@ -579,7 +582,7 @@ pub fn reset_input_cache() {
     }
 }
 
-fn get_cursor_id() -> ResultType<(id, u64, f64)> {
+fn get_cursor_id(scale: f64) -> ResultType<(id, u64)> {
     unsafe {
         let c: id = msg_send![class!(NSCursor), currentSystemCursor];
         if c == nil {
@@ -622,19 +625,25 @@ fn get_cursor_id() -> ResultType<(id, u64, f64)> {
                 hcursor += (r + g + b + a) * (255 << i) as f64;
             }
         }
-        let scale = cursor::scale()?;
-        Ok((c, cursor::cache_id(hcursor as _, scale), scale))
+        Ok((c, cursor::cache_id(hcursor as _, scale)))
     }
 }
 
 pub fn get_cursor_data(hcursor: u64) -> ResultType<CursorData> {
-    autoreleasepool(|| unsafe_get_cursor_data(hcursor))
+    let result = autoreleasepool(|| unsafe_get_cursor_data(hcursor));
+    if result.is_err() {
+        // A failed capture must be retried even if the seed and density stay unchanged.
+        reset_input_cache();
+    }
+    result
 }
 
 // https://github.com/stweil/OSXvnc/blob/master/OSXvnc-server/mousecursor.c
 fn unsafe_get_cursor_data(hcursor: u64) -> ResultType<CursorData> {
     unsafe {
-        let (c, hcursor2, scale) = get_cursor_id()?;
+        // Keep the poll's density if the pointer crosses displays before capture.
+        let scale = LATEST_SEED.1;
+        let (c, hcursor2) = get_cursor_id(scale)?;
         if hcursor != hcursor2 {
             bail!("cursor changed");
         }

src/platform/macos/cursor_poll_tests.rs

@@ -0,0 +1,17 @@
+use super::*;
+
+#[test]
+fn capture_failure_invalidates_the_density_poll() {
+    let previous = unsafe { LATEST_SEED };
+    unsafe {
+        LATEST_SEED = (1, 2.0);
+    }
+    // Zero cannot be a macOS cursor ID, even if AppKit has no current cursor.
+    let result = get_cursor_data(0);
+    let after_failure = unsafe { LATEST_SEED };
+    unsafe {
+        LATEST_SEED = previous;
+    }
+    assert!(result.is_err());
+    assert_eq!(after_failure, (0, 0.0));
+}