Behavior has been changed by several macOS updates. Share the details in the following. All issues have not been clear yet on macOS 15.0 beta 6(24A5320a) though. macOS 14.0 - macOS 14.3 : The drawing mechanism of NSView has changed significantly, and there is a problem that even if a partial area is specified with setNeedsDisplayInRect in an app program, the full area is always passed in drawRect. macOS 14.3 - macOS 14.4: The issue with setNeedsDisplayInRect has been corrected, and the partial area is now passed in drawRect. However, another issue occurred that the number of NSView drawRect and mouseDragged events gradually decreased when continuously performing setNeedsDisplayInRect on a partial area. macOS 14.5: Even if a partial area is specified in setNeedsDisplayInRect in an app program and drawn continuously, the system will now periodically draw the entire area. This change has eased the problem of events-decreasing which are described above. macOS 15.0 beta (24A5289h) : The number of events such as drawRect and mouseDragged in NSView has been dramatically reduced, so the regular full-area drawing by the system described above is no longer useful and is worse than in macOS 14.4. macOS 15.0 beta 4 (24A5298h) : It is back to macOS 14.5 equivalent behavior. macOS 15.0 beta 6 (24A5320a) : No change. Even on the latest macOS 15.0 beta 6 (24A5320a), there is an issue that the system periodically draws the whole area even if a partial area is specified in setNeedsDisplayInRect and drawn continuously. macOS 13 did not have such an issue.