relative-mouse-mode

app/src/screen.c

@@ -156,6 +156,17 @@ get_initial_optimal_size(struct sc_size content_size, uint16_t req_width,
     return window_size;
 }
 
+static inline void
+screen_capture_mouse(struct screen *screen, bool capture) {
+    if (SDL_SetRelativeMouseMode(capture)) {
+        LOGE("Could not set relative mouse mode to %s: %s",
+             capture ? "true" : "false", SDL_GetError());
+        return;
+    }
+
+    screen->mouse_captured = capture;
+}
+
 static void
 screen_update_content_rect(struct screen *screen) {
     int dw;
@@ -354,6 +365,8 @@ screen_init(struct screen *screen, const struct screen_params *params) {
     screen->fullscreen = false;
     screen->maximized = false;
     screen->event_failed = false;
+    screen->mouse_captured = false;
+    screen->mouse_capture_key_pressed = 0;
 
     static const struct sc_video_buffer_callbacks cbs = {
         .on_new_frame = sc_video_buffer_on_new_frame,
@@ -741,6 +754,11 @@ screen_resize_to_pixel_perfect(struct screen *screen) {
                                             content_size.height);
 }
 
+static inline bool
+screen_is_mouse_capture_key(SDL_Keycode key) {
+    return key == SDLK_LALT || key == SDLK_LGUI || key == SDLK_RGUI;
+}
+
 bool
 screen_handle_event(struct screen *screen, SDL_Event *event) {
     switch (event->type) {
@@ -783,8 +801,68 @@ screen_handle_event(struct screen *screen, SDL_Event *event) {
                     apply_pending_resize(screen);
                     screen_render(screen, true);
                     break;
+                case SDL_WINDOWEVENT_FOCUS_LOST:
+                    if (screen->im.mp->relative_mode) {
+                        screen_capture_mouse(screen, false);
+                    }
+                    break;
             }
             return true;
+        case SDL_KEYDOWN:
+            if (screen->im.mp->relative_mode) {
+                SDL_Keycode key = event->key.keysym.sym;
+                if (screen_is_mouse_capture_key(key)) {
+                    if (!screen->mouse_capture_key_pressed) {
+                        screen->mouse_capture_key_pressed = key;
+                        return true;
+                    } else {
+                        // Another mouse capture key has been pressed, cancel
+                        // mouse (un)capture
+                        screen->mouse_capture_key_pressed = 0;
+                        // Do not return, the event must be forwarded to the
+                        // input manager
+                    }
+                }
+            }
+            break;
+        case SDL_KEYUP:
+            if (screen->im.mp->relative_mode) {
+                SDL_Keycode key = event->key.keysym.sym;
+                SDL_Keycode cap = screen->mouse_capture_key_pressed;
+                screen->mouse_capture_key_pressed = 0;
+                if (key == cap) {
+                    // A mouse capture key has been pressed then released:
+                    // toggle the capture mouse mode
+                    screen_capture_mouse(screen, !screen->mouse_captured);
+                    return true;
+                }
+                // Do not return, the event must be forwarded to the input
+                // manager
+            }
+            break;
+        case SDL_MOUSEWHEEL:
+        case SDL_MOUSEMOTION:
+        case SDL_MOUSEBUTTONDOWN:
+            if (screen->im.mp->relative_mode && !screen->mouse_captured) {
+                // Do not forward to input manager, the mouse will be captured
+                // on SDL_MOUSEBUTTONUP
+                return true;
+            }
+            break;
+        case SDL_FINGERMOTION:
+        case SDL_FINGERDOWN:
+        case SDL_FINGERUP:
+            if (screen->im.mp->relative_mode) {
+                // Touch events are not compatible with relative mode
+                // (coordinates are not relative)
+                return true;
+            }
+            break;
+        case SDL_MOUSEBUTTONUP:
+            if (screen->im.mp->relative_mode && !screen->mouse_captured) {
+                screen_capture_mouse(screen, true);
+                return true;
+            }
     }
 
     return input_manager_handle_event(&screen->im, event);

app/src/screen.h

@@ -51,6 +51,11 @@ struct screen {
 
     bool event_failed; // in case SDL_PushEvent() returned an error
 
+    bool mouse_captured; // only relevant in relative mouse mode
+    // To enable/disable mouse capture, a mouse capture key (LALT, LGUI or
+    // RGUI) must be pressed. This variable tracks the pressed capture key.
+    SDL_Keycode mouse_capture_key_pressed;
+
     AVFrame *frame;
 };