Fixed bug 4255 - SDL_GetGlobalMouseState() returns incorrect Y on secondary display

Julian Raschke

I use an open Mac laptop with an additional external monitor. The coordinate spaces from SDL_GetGlobalMouseState() and SDL_GetWindowPosition() match on the primary display, but not on the secondary display.

Cocoa window coordinates are vertically flipped in relation to the primary display:

https://github.com/spurious/SDL-mirror/blob/release-2.0.8/src/video/cocoa/SDL_cocoawindow.m#L219-L222

However, Cocoa_GetGlobalMouseState inverts the cursor Y coordinate per-display:

https://github.com/spurious/SDL-mirror/blob/release-2.0.8/src/video/cocoa/SDL_cocoamouse.m#L320-L323

Suggested fix: Replace the for-loop with this simpler calculation:

    *x = (int) cocoaLocation.x;
    *y = (int) (CGDisplayPixelsHigh(kCGDirectMainDisplay) - cocoaLocation.y);

src/video/cocoa/SDL_cocoamouse.m

@@ -315,14 +315,8 @@ Cocoa_GetGlobalMouseState(int *x, int *y)
     const NSPoint cocoaLocation = [NSEvent mouseLocation];
     Uint32 retval = 0;
 
-    for (NSScreen *screen in [NSScreen screens]) {
-        NSRect frame = [screen frame];
-        if (NSMouseInRect(cocoaLocation, frame, NO)) {
-            *x = (int) cocoaLocation.x;
-            *y = (int) ((frame.origin.y + frame.size.height) - cocoaLocation.y);
-            break;
-        }
-    }
+    *x = (int) cocoaLocation.x;
+    *y = (int) (CGDisplayPixelsHigh(kCGDirectMainDisplay) - cocoaLocation.y);
 
     retval |= (cocoaButtons & (1 << 0)) ? SDL_BUTTON_LMASK : 0;
     retval |= (cocoaButtons & (1 << 1)) ? SDL_BUTTON_RMASK : 0;