CURSORINFO.flags should be checked before capturing its bitmap

webrtc/modules/desktop_capture/mouse_cursor_monitor_win.cc

Index: webrtc/modules/desktop_capture/mouse_cursor_monitor_win.cc
diff --git a/webrtc/modules/desktop_capture/mouse_cursor_monitor_win.cc b/webrtc/modules/desktop_capture/mouse_cursor_monitor_win.cc
index 204bb00b1602f9d32344e7f0da6145244e1979ca..479a39a021726b351b2ead41924756baab39abe5 100644
--- a/webrtc/modules/desktop_capture/mouse_cursor_monitor_win.cc
+++ b/webrtc/modules/desktop_capture/mouse_cursor_monitor_win.cc
@@ -11,10 +11,12 @@
 #include "webrtc/modules/desktop_capture/mouse_cursor_monitor.h"
 
 #include <assert.h>
+#include <string.h>
 
 #include <memory>
 
 #include "webrtc/modules/desktop_capture/desktop_frame.h"
+#include "webrtc/modules/desktop_capture/desktop_geometry.h"
 #include "webrtc/modules/desktop_capture/mouse_cursor.h"
 #include "webrtc/modules/desktop_capture/win/cursor.h"
 #include "webrtc/modules/desktop_capture/win/window_capture_utils.h"
@@ -22,6 +24,17 @@
 
 namespace webrtc {
 
+namespace {
+
+bool IsSameCursorShape(const CURSORINFO& left, const CURSORINFO& right) {
+  // If the cursors are not showing, we do not care the hCursor handle.
+  return left.flags == right.flags &&
+         (left.flags != CURSOR_SHOWING ||
+          left.hCursor == right.hCursor);
+}
+
+}  // namespace
+
 class MouseCursorMonitorWin : public MouseCursorMonitor {
  public:
   explicit MouseCursorMonitorWin(HWND window);
@@ -45,7 +58,8 @@ class MouseCursorMonitorWin : public MouseCursorMonitor {
 
   HDC desktop_dc_;
 
-  HCURSOR last_cursor_;
+  // The last CURSORINFO (converted to MouseCursor) we have sent to the client.
+  CURSORINFO last_cursor_;
 };
 
 MouseCursorMonitorWin::MouseCursorMonitorWin(HWND window)
@@ -53,8 +67,8 @@ MouseCursorMonitorWin::MouseCursorMonitorWin(HWND window)
       screen_(kInvalidScreenId),
       callback_(NULL),
       mode_(SHAPE_AND_POSITION),
-      desktop_dc_(NULL),
-      last_cursor_(NULL) {
+      desktop_dc_(NULL) {
+  memset(&last_cursor_, 0, sizeof(CURSORINFO));
 }
 
 MouseCursorMonitorWin::MouseCursorMonitorWin(ScreenId screen)
@@ -62,9 +76,9 @@ MouseCursorMonitorWin::MouseCursorMonitorWin(ScreenId screen)
       screen_(screen),
       callback_(NULL),
       mode_(SHAPE_AND_POSITION),
-      desktop_dc_(NULL),
-      last_cursor_(NULL) {
+      desktop_dc_(NULL) {
   assert(screen >= kFullDesktopScreenId);
+  memset(&last_cursor_, 0, sizeof(CURSORINFO));
 }
 
 MouseCursorMonitorWin::~MouseCursorMonitorWin() {
@@ -92,13 +106,31 @@ void MouseCursorMonitorWin::Capture() {
     return;
   }
 
-  if (last_cursor_ != cursor_info.hCursor) {
-    last_cursor_ = cursor_info.hCursor;
-    // Note that |cursor_info.hCursor| does not need to be freed.
-    std::unique_ptr<MouseCursor> cursor(
-        CreateMouseCursorFromHCursor(desktop_dc_, cursor_info.hCursor));
-    if (cursor.get())
-      callback_->OnMouseCursor(cursor.release());
+  if (!IsSameCursorShape(cursor_info, last_cursor_)) {
+    if (cursor_info.flags == CURSOR_SUPPRESSED) {
+      // The cursor is intentionally hidden now, send an empty bitmap.
+      last_cursor_ = cursor_info;
+      callback_->OnMouseCursor(new MouseCursor(
+          new BasicDesktopFrame(DesktopSize()), DesktopVector()));
+    } else {
+      // According to MSDN https://goo.gl/u6gyuC, HCURSOR instances returned by
+      // functions other than CreateCursor do not need to be actively destroyed.
+      // And CloseHandle function (https://goo.gl/ja5ycW) does not close a
+      // cursor, so assume a HCURSOR does not need to be closed.
+      if (cursor_info.flags == 0) {
+        // Host machine does not have a hardware mouse attached, we will send a
+        // default one instead.
+        // Note, Windows automatically caches cursor resource, so we do not need
+        // to cache the result of LoadCursor.
+        cursor_info.hCursor = LoadCursor(nullptr, IDC_ARROW);
+      }
+      std::unique_ptr<MouseCursor> cursor(
+          CreateMouseCursorFromHCursor(desktop_dc_, cursor_info.hCursor));
+      if (cursor) {
+        last_cursor_ = cursor_info;
+        callback_->OnMouseCursor(cursor.release());
+      }
+    }
   }
 
   if (mode_ != SHAPE_AND_POSITION)