Added a relative mouse mode that uses mouse warping instead of raw input.

To enable this, set the environment variable SDL_MOUSE_RELATIVE_MODE_WARP to "1"

When mouse relative mode is disabled, put the cursor back where the application expects it to be, instead of where it was when relative mode was enabled.

include/SDL_hints.h

@@ -173,7 +173,18 @@ extern "C" {
 #define SDL_HINT_GRAB_KEYBOARD              "SDL_GRAB_KEYBOARD"
 
 /**
- *  \brief Minimize your SDL_Window if it loses key focus when in Fullscreen mode. Defaults to true.
+*  \brief  A variable controlling whether relative mouse mode is implemented using mouse warping
+*
+*  This variable can be set to the following values:
+*    "0"       - Relative mouse mode uses raw input
+*    "1"       - Relative mouse mode uses mouse warping
+*
+*  By default SDL will use raw input for relative mouse mode
+*/
+#define SDL_HINT_MOUSE_RELATIVE_MODE_WARP    "SDL_MOUSE_RELATIVE_MODE_WARP"
+
+/**
+ *  \brief Minimize your SDL_Window if it loses key focus when in fullscreen mode. Defaults to true.
  *
  */
 #define SDL_HINT_VIDEO_MINIMIZE_ON_FOCUS_LOSS   "SDL_VIDEO_MINIMIZE_ON_FOCUS_LOSS"

src/events/SDL_mouse.c

@@ -23,6 +23,7 @@
 /* General mouse handling code for SDL */
 
 #include "SDL_assert.h"
+#include "SDL_hints.h"
 #include "SDL_timer.h"
 #include "SDL_events.h"
 #include "SDL_events_c.h"
@@ -205,12 +206,24 @@ SDL_PrivateSendMouseMotion(SDL_Window * window, SDL_MouseID mouseID, int relativ
     int yrel;
     int x_max = 0, y_max = 0;
 
-    /* relative motion is calculated regarding the system cursor last position */
+    if (mouse->relative_mode_warp) {
+        int center_x = 0, center_y = 0;
+        SDL_GetWindowSize(window, &center_x, &center_y);
+        center_x /= 2;
+        center_y /= 2;
+        if (x == center_x && y == center_y) {
+            mouse->last_x = center_x;
+            mouse->last_y = center_y;
+            return 0;
+        }
+        SDL_WarpMouseInWindow(window, center_x, center_y);
+    }
+
     if (relative) {
         xrel = x;
         yrel = y;
-        x = (mouse->last_x + x);
-        y = (mouse->last_y + y);
+        x = (mouse->last_x + xrel);
+        y = (mouse->last_y + yrel);
     } else {
         xrel = x - mouse->last_x;
         yrel = y - mouse->last_y;
@@ -225,7 +238,7 @@ SDL_PrivateSendMouseMotion(SDL_Window * window, SDL_MouseID mouseID, int relativ
     }
 
     /* Update internal mouse coordinates */
-    if (mouse->relative_mode == SDL_FALSE) {
+    if (!mouse->relative_mode) {
         mouse->x = x;
         mouse->y = y;
     } else {
@@ -481,21 +494,36 @@ SDL_WarpMouseInWindow(SDL_Window * window, int x, int y)
     }
 }
 
+static SDL_bool
+ShouldUseRelativeModeWarp(SDL_Mouse *mouse)
+{
+    const char *hint;
+
+    if (!mouse->SetRelativeMouseMode) {
+        return SDL_TRUE;
+    }
+
+    hint = SDL_GetHint(SDL_HINT_MOUSE_RELATIVE_MODE_WARP);
+    if (hint) {
+        if (*hint == '0') {
+            return SDL_FALSE;
+        } else {
+            return SDL_TRUE;
+        }
+    }
+    return SDL_FALSE;
+}
+
 int
 SDL_SetRelativeMouseMode(SDL_bool enabled)
 {
     SDL_Mouse *mouse = SDL_GetMouse();
     SDL_Window *focusWindow = SDL_GetKeyboardFocus();
-    int original_x = mouse->x, original_y = mouse->y;
 
     if (enabled == mouse->relative_mode) {
         return 0;
     }
 
-    if (!mouse->SetRelativeMouseMode) {
-        return SDL_Unsupported();
-    }
-
     if (enabled && focusWindow) {
         /* Center it in the focused window to prevent clicks from going through
          * to background windows.
@@ -504,23 +532,26 @@ SDL_SetRelativeMouseMode(SDL_bool enabled)
         SDL_WarpMouseInWindow(focusWindow, focusWindow->w/2, focusWindow->h/2);
     }
 
-    if (mouse->SetRelativeMouseMode(enabled) < 0) {
+    /* Set the relative mode */
+    if (!enabled && mouse->relative_mode_warp) {
+        mouse->relative_mode_warp = SDL_FALSE;
+    } else if (enabled && ShouldUseRelativeModeWarp(mouse)) {
+        mouse->relative_mode_warp = SDL_TRUE;
+    } else if (mouse->SetRelativeMouseMode(enabled) < 0) {
         return -1;
     }
-
-    /* Set the relative mode */
     mouse->relative_mode = enabled;
 
-    if (enabled) {
-        /* Save the expected mouse position */
-        mouse->original_x = original_x;
-        mouse->original_y = original_y;
-    } else if (mouse->focus) {
-        /* Restore the expected mouse position */
-        SDL_WarpMouseInWindow(mouse->focus, mouse->original_x, mouse->original_y);
+    if (mouse->focus) {
+        SDL_UpdateWindowGrab(mouse->focus);
+
+        /* Put the cursor back to where the application expects it */
+        if (!enabled) {
+            SDL_WarpMouseInWindow(mouse->focus, mouse->x, mouse->y);
+        }
     }
 
-    /* Flush pending mouse motion */
+    /* Flush pending mouse motion - ideally we would pump events, but that's not always safe */
     SDL_FlushEvent(SDL_MOUSEMOTION);
 
     /* Update cursor visibility */

src/events/SDL_mouse_c.h

@@ -73,8 +73,7 @@ typedef struct
     int last_x, last_y;         /* the last reported x and y coordinates */
     Uint32 buttonstate;
     SDL_bool relative_mode;
-    /* the x and y coordinates when relative mode was activated */
-    int original_x, original_y;
+    SDL_bool relative_mode_warp;
 
     /* Data for double-click tracking */
     int num_clickstates;

src/video/SDL_video.c

@@ -2055,8 +2055,9 @@ SDL_UpdateWindowGrab(SDL_Window * window)
 {
     if (_this->SetWindowGrab) {
         SDL_bool grabbed;
-        if ((window->flags & SDL_WINDOW_INPUT_GRABBED) &&
-            (window->flags & SDL_WINDOW_INPUT_FOCUS)) {
+        if (SDL_GetMouse()->relative_mode_warp ||
+            ((window->flags & SDL_WINDOW_INPUT_GRABBED) &&
+             (window->flags & SDL_WINDOW_INPUT_FOCUS))) {
             grabbed = SDL_TRUE;
         } else {
             grabbed = SDL_FALSE;

src/video/windows/SDL_windowsevents.c

@@ -290,6 +290,7 @@ static void
 WIN_UpdateClipCursor(SDL_Window *window)
 {
     SDL_WindowData *data = (SDL_WindowData *) window->driverdata;
+    SDL_Mouse *mouse = SDL_GetMouse();
 
     /* Don't clip the cursor while we're in the modal resize or move loop */
     if (data->in_modal_loop) {
@@ -297,7 +298,7 @@ WIN_UpdateClipCursor(SDL_Window *window)
         return;
     }
         
-    if (SDL_GetMouse()->relative_mode) {
+    if (mouse->relative_mode && !mouse->relative_mode_warp) {
         LONG cx, cy;
         RECT rect;
         GetWindowRect(data->hwnd, &rect);
@@ -312,8 +313,9 @@ WIN_UpdateClipCursor(SDL_Window *window)
         rect.bottom = cy+1;
 
         ClipCursor(&rect);
-    } else if ((window->flags & SDL_WINDOW_INPUT_GRABBED) &&
-               (window->flags & SDL_WINDOW_INPUT_FOCUS)) {
+    } else if (mouse->relative_mode_warp ||
+               ((window->flags & SDL_WINDOW_INPUT_GRABBED) &&
+                (window->flags & SDL_WINDOW_INPUT_FOCUS))) {
         RECT rect;
         if (GetClientRect(data->hwnd, &rect) && !IsRectEmpty(&rect)) {
             ClientToScreen(data->hwnd, (LPPOINT) & rect);
@@ -426,8 +428,12 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
         break;
 
     case WM_MOUSEMOVE:
-        if( !SDL_GetMouse()->relative_mode )
-            SDL_SendMouseMotion(data->window, 0, 0, GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam));
+        {
+            SDL_Mouse *mouse = SDL_GetMouse();
+            if (!mouse->relative_mode || mouse->relative_mode_warp) {
+                SDL_SendMouseMotion(data->window, 0, 0, GET_X_LPARAM(lParam), GET_Y_LPARAM(lParam));
+            }
+        }
         /* don't break here, fall through to check the wParam like the button presses */
     case WM_LBUTTONUP:
     case WM_RBUTTONUP:
@@ -437,49 +443,50 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
     case WM_RBUTTONDOWN:
     case WM_MBUTTONDOWN:
     case WM_XBUTTONDOWN:
-        if( !SDL_GetMouse()->relative_mode )
-            WIN_CheckWParamMouseButtons( wParam, data );
+        {
+            SDL_Mouse *mouse = SDL_GetMouse();
+            if (!mouse->relative_mode || mouse->relative_mode_warp) {
+                WIN_CheckWParamMouseButtons(wParam, data);
+            }
+        }
         break;
 
     case WM_INPUT:
-    {
-        HRAWINPUT hRawInput = (HRAWINPUT)lParam;
-        RAWINPUT inp;
-        UINT size = sizeof(inp);
+        {
+            SDL_Mouse *mouse = SDL_GetMouse();
+            HRAWINPUT hRawInput = (HRAWINPUT)lParam;
+            RAWINPUT inp;
+            UINT size = sizeof(inp);
 
-        if(!SDL_GetMouse()->relative_mode)
-            break;
+            if (!mouse->relative_mode || mouse->relative_mode_warp) {
+                break;
+            }
 
-        GetRawInputData(hRawInput, RID_INPUT, &inp, &size, sizeof(RAWINPUTHEADER));
+            GetRawInputData(hRawInput, RID_INPUT, &inp, &size, sizeof(RAWINPUTHEADER));
 
-        /* Mouse data */
-        if(inp.header.dwType == RIM_TYPEMOUSE)
-        {
-            RAWMOUSE* mouse = &inp.data.mouse;
+            /* Mouse data */
+            if (inp.header.dwType == RIM_TYPEMOUSE) {
+                RAWMOUSE* mouse = &inp.data.mouse;
+
+                if ((mouse->usFlags & 0x01) == MOUSE_MOVE_RELATIVE) {
+                    SDL_SendMouseMotion(data->window, 0, 1, (int)mouse->lLastX, (int)mouse->lLastY);
+                } else {
+                    /* synthesize relative moves from the abs position */
+                    static SDL_Point initialMousePoint;
+                    if (initialMousePoint.x == 0 && initialMousePoint.y == 0) {
+                        initialMousePoint.x = mouse->lLastX;
+                        initialMousePoint.y = mouse->lLastY;
+                    }
+
+                    SDL_SendMouseMotion(data->window, 0, 1, (int)(mouse->lLastX-initialMousePoint.x), (int)(mouse->lLastY-initialMousePoint.y) );
 
-            if((mouse->usFlags & 0x01) == MOUSE_MOVE_RELATIVE)
-            {
-                SDL_SendMouseMotion(data->window, 0, 1, (int)mouse->lLastX, (int)mouse->lLastY);
-            }
-            else
-            {
-                /* synthesize relative moves from the abs position */
-                static SDL_Point initialMousePoint;
-                if ( initialMousePoint.x == 0 && initialMousePoint.y == 0 )
-                {
                     initialMousePoint.x = mouse->lLastX;
                     initialMousePoint.y = mouse->lLastY;
                 }
-
-                SDL_SendMouseMotion(data->window, 0, 1, (int)(mouse->lLastX-initialMousePoint.x), (int)(mouse->lLastY-initialMousePoint.y) );
-
-                initialMousePoint.x = mouse->lLastX;
-                initialMousePoint.y = mouse->lLastY;
+                WIN_CheckRawMouseButtons( mouse->usButtonFlags, data );
             }
-            WIN_CheckRawMouseButtons( mouse->usButtonFlags, data );
         }
         break;
-    }
 
     case WM_MOUSEWHEEL:
         {
@@ -497,8 +504,8 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
                     s_AccumulatedMotion += WHEEL_DELTA;
                 }
             }
-            break;
         }
+        break;
 
     case WM_MOUSEHWHEEL:
         {
@@ -516,8 +523,8 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
                     s_AccumulatedMotion += WHEEL_DELTA;
                 }
             }
-            break;
         }
+        break;
 
 #ifdef WM_MOUSELEAVE
     case WM_MOUSELEAVE:
@@ -549,8 +556,8 @@ WIN_WindowProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam)
 
             GetKeyboardState(keyboardState);
             if (ToUnicode(wParam, (lParam >> 16) & 0xff, keyboardState, (LPWSTR)&utf32, 1, 0) > 0) {
-                WORD repitition;
-                for (repitition = lParam & 0xffff; repitition > 0; repitition--) {
+                WORD repetition;
+                for (repetition = lParam & 0xffff; repetition > 0; repetition--) {
                     WIN_ConvertUTF32toUTF8(utf32, text);
                     SDL_SendKeyboardText(text);
                 }

src/video/x11/SDL_x11events.c

@@ -698,7 +698,7 @@ X11_DispatchEvent(_THIS)
 
     case MotionNotify:{
             SDL_Mouse *mouse = SDL_GetMouse();
-            if(!mouse->relative_mode) {
+            if(!mouse->relative_mode || mouse->relative_mode_warp) {
 #ifdef DEBUG_MOTION
                 printf("window %p: X11 motion: %d,%d\n", xevent.xmotion.x, xevent.xmotion.y);
 #endif

src/video/x11/SDL_x11xinput2.c

@@ -134,7 +134,7 @@ X11_HandleXinput2Event(SDL_VideoData *videodata,XGenericEventCookie *cookie)
             SDL_Mouse *mouse = SDL_GetMouse();
             double relative_cords[2];
 
-            if (!mouse->relative_mode) {
+            if (!mouse->relative_mode || mouse->relative_mode_warp) {
                 return 0;
             }