make mouse movement and capture depend on window focus

src/twn_engine_context_c.h

@@ -82,6 +82,8 @@ typedef struct EngineContext {
     bool resync_flag;
     bool was_successful;
     bool render_double_buffered;
+    /* signals mouse focus, used to disable mouse capture */
+    bool window_mouse_resident;
 } EngineContext;
 
 /* TODO: does it need to be marked with TWN_API? */

src/twn_input.c

@@ -218,7 +218,7 @@ void input_state_deinit(InputState *input) {
 
 void input_state_update(InputState *input) {
     /* TODO: don't spam it if it happens */
-    if (SDL_SetRelativeMouseMode(ctx.game_copy.mouse_capture) != 0)
+    if (SDL_SetRelativeMouseMode(ctx.game_copy.mouse_capture && ctx.window_mouse_resident) != 0)
         log_warn("(%s) Mouse capture isn't supported.", __func__);
 
     int x, y;
@@ -231,6 +231,8 @@ void input_state_update(InputState *input) {
     input->mouse_relative_position = (Vec2){ (float)x, (float)y };
 
     ctx.game.mouse_position = input->mouse_window_position;
+
+    if (ctx.window_mouse_resident)
         ctx.game.mouse_movement = input->mouse_relative_position;
 
     for (size_t i = 0; i < shlenu(input->action_hash); ++i) {

src/twn_loop.c

@@ -42,6 +42,16 @@ static int event_callback(void *userdata, SDL_Event *event) {
             ctx.resync_flag = true;
             break;
 
+        case SDL_WINDOWEVENT_FOCUS_LOST: {
+            ctx.window_mouse_resident = false;
+            break;
+        }
+
+        case SDL_WINDOWEVENT_FOCUS_GAINED: {
+            ctx.window_mouse_resident = true;
+            break;
+        }
+
         default:
             break;
         }
@@ -706,6 +716,7 @@ static bool initialize(void) {
     */
 
     ctx.render_double_buffered = true;
+    ctx.window_mouse_resident = true;
 
     return true;