SDL2: drain event queue every frame + relative mouse mode during gameplay (#49)

src/core/Pad.cpp

@@ -890,6 +890,11 @@ CMouseControllerState CMousePointerStateHelper::GetMouseSetUp()
 	return state;
 }
 
+#ifdef LIBRW_SDL2
+bool _InputMouseIsRelative(void);
+void _InputConsumeMouseRelative(int *dx, int *dy);
+#endif
+
 void CPad::UpdateMouse()
 {
 #if defined RW_D3D9 || defined RWLIBS
@@ -942,8 +947,13 @@ void CPad::UpdateMouse()
         double xpos = 1.0f, ypos;
 		glfwGetCursorPos(PSGLOBAL(window), &xpos, &ypos);
 #endif
+		#ifdef LIBRW_SDL2
+		        if (!_InputMouseIsRelative() && xpos == 0)
+		            return;
+		#else
 		        if (xpos == 0.f)
 		            return;
+		#endif
 
 		int32 signX = 1;
 		int32 signy = 1;
@@ -958,8 +968,20 @@ void CPad::UpdateMouse()
 
 		PCTempMouseControllerState.Clear();
 
+		#ifdef LIBRW_SDL2
+		        if (_InputMouseIsRelative()) {
+		            // true relative deltas from the motion events; polled positions are
+		            // confined and stall at window/monitor edges
+		            int dx, dy;
+		            _InputConsumeMouseRelative(&dx, &dy);
+		            PCTempMouseControllerState.x = (float)(signX * dx);
+		            PCTempMouseControllerState.y = (float)(signy * dy);
+		        } else
+		#endif
+		        {
 		            PCTempMouseControllerState.x = (float)(signX * (xpos - PSGLOBAL(lastMousePos.x)));
 		            PCTempMouseControllerState.y = (float)(signy * (ypos - PSGLOBAL(lastMousePos.y)));
+		        }
 #ifdef LIBRW_SDL2
         PCTempMouseControllerState.LMB = !!(mouseState & SDL_BUTTON(1));
         PCTempMouseControllerState.RMB = !!(mouseState & SDL_BUTTON(3));

src/skel/sdl2/sdl2.cpp

@@ -784,6 +784,24 @@ bool _InputMouseNeedsExclusive()
     return false;
 }
 
+// Relative mouse support: the game derives deltas from polled positions,
+// but confined positions stall at window/monitor edges. Accumulate the true
+// deltas from the motion events instead; the game consumes them once per frame.
+static bool mouseRelativeMode = false;
+static int mouseRelX = 0, mouseRelY = 0;
+
+bool _InputMouseIsRelative(void)
+{
+    return mouseRelativeMode;
+}
+
+void _InputConsumeMouseRelative(int *dx, int *dy)
+{
+    *dx = mouseRelX;
+    *dy = mouseRelY;
+    mouseRelX = mouseRelY = 0;
+}
+
 void psPostRWinit(void)
 {
     RwVideoMode vm;
@@ -1268,9 +1286,12 @@ cursorEnterCB(int entered) {
     PSGLOBAL(cursorIsInWindow) = !!entered;
 }
 
-void
-windowFocusCB(int focused) {
+void windowFocusCB(int focused) {
     WindowFocused = !!focused;
+    if (!focused) {
+        // deltas accumulated while unfocused must not fire on refocus
+        mouseRelX = mouseRelY = 0;
+    }
 }
 
 void
@@ -1281,14 +1302,18 @@ windowIconifyCB(int iconified) {
 void inputEventHandler() {
     SDL_Event event;
 
-    if (SDL_PollEvent(&event)) {
+    while (SDL_PollEvent(&event)) {
         switch (event.type) {
             case SDL_KEYDOWN:	/* fall-through */
             case SDL_KEYUP:
                 keypressCB(event.key.keysym.sym, event.type, 0);
                 break;
 
-            case SDL_MOUSEMOTION: cursorCB(event.motion.x, event.motion.y); break;
+            case SDL_MOUSEMOTION:
+                cursorCB(event.motion.x, event.motion.y);
+                mouseRelX += event.motion.xrel;
+                mouseRelY += event.motion.yrel;
+                break;
             case SDL_MOUSEWHEEL: scrollCB(event.wheel.x, event.wheel.y); break;
 
             // note that SDL_CONTROLLERDEVICEADDED/REMOVED exists, but it did not work for me
@@ -1313,6 +1338,34 @@ void inputEventHandler() {
                 break;
         }
     }
+
+    // Grab the mouse during gameplay (GLFW_CURSOR_DISABLED equivalent):
+    // relative motion + pointer confinement, so the hidden cursor can't
+    // wander off to another monitor or stall at the window edge.
+    // The frontend needs absolute positions, so keep it free there.
+    bool wantRelative = gGameState == GS_PLAYING_GAME &&
+                        !FrontEndMenuManager.m_bMenuActive && !WindowIconified;
+    if (wantRelative != mouseRelativeMode) {
+        if (SDL_SetRelativeMouseMode(wantRelative ? SDL_TRUE : SDL_FALSE) == 0) {
+            mouseRelativeMode = wantRelative;
+            mouseRelX = mouseRelY = 0;
+            if (wantRelative) {
+                PSGLOBAL(cursorIsInWindow) = true;
+            } else {
+                int x, y;
+                SDL_GetMouseState(&x, &y);
+                PSGLOBAL(lastMousePos.x) = x;
+                PSGLOBAL(lastMousePos.y) = y;
+            }
+        } else {
+            // switch failed: never leave the menu with a grabbed pointer and
+            // garbage coordinates — release the grab and fall back to polling
+            SDL_SetWindowGrab(PSGLOBAL(window), SDL_FALSE);
+            SDL_ShowCursor(SDL_DISABLE);
+            mouseRelativeMode = false;
+        }
+    }
+    
 }
 
 /*