Reverted change for bug 4152 - restrict the win10 mouse bug workaround to win10 v1709 only

Daniel Gibson

Sorry, but it seems like Microsoft didn't fix the issue properly.

I just updated my Win10 machine, it now is Version 1803, Build 17134.1

I tested with SDL2 2.0.7 (my workaround was released with 2.0.8) and still got
lots of events that directly undid the prior "real" events - just like before.
(See simple testcase in attachement)
By default it sets SDL_HINT_MOUSE_RELATIVE_MODE_WARP - which triggered (and on my machine still triggers) the buggy behavior. You can start it with -raw, then it'll not set that hint and the events will be as expected.
The easiest way to see the difference is looking at the window title, which shows accumulated X and Y values: If you just move your mouse to the right, in -raw mode the number just increases. In non-raw mode (using mouse warping) it stays around 0.

I also had a WinAPI-only testcase: https://gist.github.com/DanielGibson/b5b033c67b9137f0280af9fc53352c68
It just calls SetCursorPos(320,240); on each WM_MOUSEMOVE event, and it also
logs all those events to a mouseevents.log textfile.
This log indeed looks a bit different since the latest Win10 update: It seems like all those events with x=320 y=240 do arrive - but only after I stopped moving the mouse - even though the cursor seems to be moved back every frame (or so).
So moving the mouse to the right gives X coordinates like
330, 325, 333, 340, 330, ...
and then when stopping movement I get lots of events with X coordinate 320

src/video/windows/SDL_windowsevents.c

@@ -359,6 +359,11 @@ ShouldGenerateWindowCloseOnAltF4(void)
     return !SDL_GetHintBoolean(SDL_HINT_WINDOWS_NO_CLOSE_ON_ALT_F4, SDL_FALSE);
 }
 
+/* Win10 "Fall Creators Update" introduced the bug that SetCursorPos() (as used by SDL_WarpMouseInWindow())
+   doesn't reliably generate WM_MOUSEMOVE events anymore (see #3931) which breaks relative mouse mode via warping.
+   This is used to implement a workaround.. */
+static SDL_bool isWin10FCUorNewer = SDL_FALSE;
+
 LRESULT CALLBACK
 WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
 {
@@ -481,6 +486,17 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
             if (!mouse->relative_mode || mouse->relative_mode_warp) {
                 SDL_MouseID mouseID = (((GetMessageExtraInfo() & MOUSEEVENTF_FROMTOUCH) == MOUSEEVENTF_FROMTOUCH) ? SDL_TOUCH_MOUSEID : 0);
                 SDL_SendMouseMotion(data->window, mouseID, 0, GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam));
+                if (isWin10FCUorNewer && mouseID != SDL_TOUCH_MOUSEID && mouse->relative_mode_warp) {
+                    /* To work around #3931, Win10 bug introduced in Fall Creators Update, where
+                       SetCursorPos() (SDL_WarpMouseInWindow()) doesn't reliably generate mouse events anymore,
+                       after each windows mouse event generate a fake event for the middle of the window
+                       if relative_mode_warp is used */
+                    int center_x = 0, center_y = 0;
+                    SDL_GetWindowSize(data->window, &center_x, &center_y);
+                    center_x /= 2;
+                    center_y /= 2;
+                    SDL_SendMouseMotion(data->window, mouseID, 0, center_x, center_y);
+                }
             }
         }
         /* don't break here, fall through to check the wParam like the button presses */
@@ -1058,6 +1074,43 @@ WIN_PumpEvents(_THIS)
     }
 }
 
+/* to work around #3931, a bug introduced in Win10 Fall Creators Update (build nr. 16299)
+   we need to detect the windows version. this struct and the function below does that.
+   usually this struct and the corresponding function (RtlGetVersion) are in <Ntddk.h>
+   but here we just load it dynamically */
+struct SDL_WIN_OSVERSIONINFOW {
+    ULONG dwOSVersionInfoSize;
+    ULONG dwMajorVersion;
+    ULONG dwMinorVersion;
+    ULONG dwBuildNumber;
+    ULONG dwPlatformId;
+    WCHAR szCSDVersion[128];
+};
+
+static SDL_bool
+IsWin10FCUorNewer(void)
+{
+    HMODULE handle = GetModuleHandleW(L"ntdll.dll");
+    if (handle) {
+        typedef LONG(WINAPI* RtlGetVersionPtr)(struct SDL_WIN_OSVERSIONINFOW*);
+        RtlGetVersionPtr getVersionPtr = (RtlGetVersionPtr)GetProcAddress(handle, "RtlGetVersion");
+        if (getVersionPtr != NULL) {
+            struct SDL_WIN_OSVERSIONINFOW info;
+            SDL_zero(info);
+            info.dwOSVersionInfoSize = sizeof(info);
+            if (getVersionPtr(&info) == 0) { /* STATUS_SUCCESS == 0 */
+                if (   (info.dwMajorVersion == 10 && info.dwMinorVersion == 0 && info.dwBuildNumber >= 16299)
+                    || (info.dwMajorVersion == 10 && info.dwMinorVersion > 0)
+                    || (info.dwMajorVersion > 10) )
+                {
+                    return SDL_TRUE;
+                }
+            }
+        }
+    }
+    return SDL_FALSE;
+}
+
 static int app_registered = 0;
 LPTSTR SDL_Appname = NULL;
 Uint32 SDL_Appstyle = 0;
@@ -1122,6 +1175,8 @@ SDL_RegisterApp(char *name, Uint32 style, void *hInst)
         return SDL_SetError("Couldn't register application class");
     }
 
+    isWin10FCUorNewer = IsWin10FCUorNewer();
+
     app_registered = 1;
     return 0;
 }