Add resizable virtual display feature

Introduce `--flex-display` to continuously resize the virtual display
to match the window.

app/src/cli.c

@@ -791,7 +791,8 @@ static const struct sc_option options[] = {
                 "and bottom or at the sides if needed).\n"
                 "\"disabled\": render the display at the top-left corner, "
                 "without scaling.\n"
-                "Default is \"letterbox\".",
+                "Default is \"letterbox\", unless --flex-display is set, in "
+                "which case it is \"disabled\".",
     },
     {
         .longopt_id = OPT_REQUIRE_AUDIO,
@@ -1016,6 +1017,11 @@ static const struct sc_option options[] = {
         .text = "Set the initial window height.\n"
                 "Default is 0 (automatic).",
     },
+    {
+        .shortopt = 'x',
+        .longopt = "flex-display",
+        .text = "Continuously resize the virtual display to match the window.",
+    },
 };
 
 static const struct sc_shortcut shortcuts[] = {
@@ -2792,6 +2798,9 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
                     return false;
                 }
                 break;
+            case 'x':
+                opts->flex_display = true;
+                break;
             default:
                 // getopt prints the error message on stderr
                 return false;
@@ -2971,6 +2980,11 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
         }
     }
 
+    if (opts->render_fit == SC_RENDER_FIT_AUTO) {
+        opts->render_fit = opts->flex_display ? SC_RENDER_FIT_DISABLED
+                                              : SC_RENDER_FIT_LETTERBOX;
+    }
+
     if (otg) {
         if (!opts->control) {
             LOGE("--no-control is not allowed in OTG mode");
@@ -3090,6 +3104,28 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
         return false;
     }
 
+    if (opts->flex_display) {
+        if (opts->video_source != SC_VIDEO_SOURCE_DISPLAY
+                || !opts->new_display) {
+            LOGE("-x/--flex-display can only be applied to displays created "
+                 "with --new-display");
+            return false;
+        }
+
+        if (opts->max_size) {
+            LOGE("--max-size is not compatible with -x/--flex-display");
+            return false;
+        }
+
+        if (opts->crop) {
+            LOGE("--crop is not compatible with -x/--flex-display");
+            return false;
+        }
+
+        // Force free resizing
+        opts->window_aspect_ratio_lock = false;
+    }
+
     if (opts->display_ime_policy != SC_DISPLAY_IME_POLICY_UNDEFINED
             && opts->display_id == 0 && !opts->new_display) {
         LOGE("--display-ime-policy is only supported on a secondary display");

app/src/options.c

@@ -59,7 +59,7 @@ const struct scrcpy_options scrcpy_options_default = {
     .display_orientation = SC_ORIENTATION_0,
     .record_orientation = SC_ORIENTATION_0,
     .display_ime_policy = SC_DISPLAY_IME_POLICY_UNDEFINED,
-    .render_fit = SC_RENDER_FIT_LETTERBOX,
+    .render_fit = SC_RENDER_FIT_AUTO,
     .window_x = SC_WINDOW_POSITION_UNDEFINED,
     .window_y = SC_WINDOW_POSITION_UNDEFINED,
     .window_width = 0,
@@ -117,6 +117,7 @@ const struct scrcpy_options scrcpy_options_default = {
     .vd_destroy_content = true,
     .vd_system_decorations = true,
     .camera_torch = false,
+    .flex_display = false,
 };
 
 enum sc_orientation

app/src/options.h

@@ -221,6 +221,7 @@ enum sc_shortcut_mod {
 };
 
 enum sc_render_fit {
+    SC_RENDER_FIT_AUTO,
     SC_RENDER_FIT_LETTERBOX,
     SC_RENDER_FIT_DISABLED,
 };
@@ -336,6 +337,7 @@ struct scrcpy_options {
     bool vd_destroy_content;
     bool vd_system_decorations;
     bool camera_torch;
+    bool flex_display;
 };
 
 extern const struct scrcpy_options scrcpy_options_default;

app/src/scrcpy.c

@@ -465,6 +465,7 @@ scrcpy(struct scrcpy_options *options) {
         .camera_zoom = options->camera_zoom,
         .vd_destroy_content = options->vd_destroy_content,
         .vd_system_decorations = options->vd_system_decorations,
+        .flex_display = options->flex_display,
         .list = options->list,
     };
 
@@ -797,6 +798,7 @@ aoa_complete:
         struct sc_screen_params screen_params = {
             .video = options->video_playback,
             .camera = options->video_source == SC_VIDEO_SOURCE_CAMERA,
+            .flex_display = options->flex_display,
             .controller = controller,
             .fp = fp,
             .kp = kp,

app/src/screen.c

@@ -286,10 +286,27 @@ end:
 }
 
 static void
-sc_screen_on_resize(struct sc_screen *screen) {
+sc_screen_on_resize(struct sc_screen *screen, const SDL_WindowEvent *event) {
     // This event can be triggered before the window is shown
     if (screen->window_shown) {
         sc_screen_render(screen, true);
+
+        if (screen->flex_display) {
+            assert(!screen->camera);
+            assert(!(event->data1 & !0xFFFF));
+            assert(!(event->data2 & !0xFFFF));
+            uint16_t width = event->data1;
+            uint16_t height = event->data2;
+            if (sc_orientation_is_swap(screen->orientation)) {
+                uint16_t tmp = width;
+                width = height;
+                height = tmp;
+            }
+
+            LOGV("resize_display(%" PRIu16 ", %" PRIu16 ")", width, height);
+            sc_controller_resize_display(screen->controller, width,
+                                         height);
+        }
     }
 }
 
@@ -311,7 +328,7 @@ event_watcher(void *data, SDL_Event *event) {
     if (event->type == SDL_EVENT_WINDOW_PIXEL_SIZE_CHANGED) {
         // In practice, it seems to always be called from the same thread in
         // that specific case. Anyway, it's just a workaround.
-        sc_screen_on_resize(screen);
+        sc_screen_on_resize(screen, &event->window);
     }
 
     return true;
@@ -406,6 +423,8 @@ sc_screen_frame_sink_push_session(struct sc_frame_sink *sink,
 bool
 sc_screen_init(struct sc_screen *screen,
                const struct sc_screen_params *params) {
+    screen->controller = params->controller;
+
     screen->resize_pending = false;
     screen->window_shown = false;
     screen->paused = false;
@@ -418,6 +437,7 @@ sc_screen_init(struct sc_screen *screen,
     screen->camera = params->camera;
     screen->window_aspect_ratio_lock = params->window_aspect_ratio_lock;
     screen->render_fit = params->render_fit;
+    screen->flex_display = params->flex_display;
 
     screen->req.x = params->window_x;
     screen->req.y = params->window_y;
@@ -739,11 +759,13 @@ resize_for_content(struct sc_screen *screen, struct sc_size old_content_size,
     assert(screen->video);
 
     struct sc_size window_size = sc_sdl_get_window_size(screen->window);
-    struct sc_size target_size = {
-        .width = (uint32_t) window_size.width * new_content_size.width
-                / old_content_size.width,
-        .height = (uint32_t) window_size.height * new_content_size.height
-                / old_content_size.height,
+    struct sc_size target_size = new_content_size;
+    if (!screen->flex_display) {
+        // Scale proportionally
+        target_size.width = (uint32_t) window_size.width * target_size.width
+                          / old_content_size.width;
+        target_size.height = (uint32_t) window_size.height * target_size.height
+                           / old_content_size.height;
     };
     target_size = get_optimal_size(target_size, new_content_size, true);
     assert(is_windowed(screen));
@@ -999,7 +1021,7 @@ sc_screen_handle_event(struct sc_screen *screen, const SDL_Event *event) {
 // If defined, then the actions are already performed by the event watcher
 #ifndef CONTINUOUS_RESIZING_WORKAROUND
         case SDL_EVENT_WINDOW_PIXEL_SIZE_CHANGED:
-            sc_screen_on_resize(screen);
+            sc_screen_on_resize(screen, &event->window);
             return;
 #endif
         case SDL_EVENT_WINDOW_RESTORED:

app/src/screen.h

@@ -37,6 +37,9 @@ struct sc_screen {
     bool video;
     bool camera;
     bool window_aspect_ratio_lock;
+    bool flex_display;
+
+    struct sc_controller *controller;
 
     struct sc_texture tex;
     struct sc_input_manager im;
@@ -96,6 +99,7 @@ struct sc_screen {
 struct sc_screen_params {
     bool video;
     bool camera;
+    bool flex_display;
 
     struct sc_controller *controller;
     struct sc_file_pusher *fp;

app/src/server.c

@@ -413,6 +413,9 @@ execute_server(struct sc_server *server,
         VALIDATE_STRING(params->new_display);
         ADD_PARAM("new_display=%s", params->new_display);
     }
+    if (params->flex_display) {
+        ADD_PARAM("flex_display=true");
+    }
     if (params->display_ime_policy != SC_DISPLAY_IME_POLICY_UNDEFINED) {
         ADD_PARAM("display_ime_policy=%s",
             sc_server_get_display_ime_policy_name(params->display_ime_policy));

app/src/server.h

@@ -72,6 +72,7 @@ struct sc_server_params {
     bool camera_torch;
     bool vd_destroy_content;
     bool vd_system_decorations;
+    bool flex_display;
     uint8_t list;
 };