Add multitouch simulation

While the Ctrl key is held, the first left-click adds an immobile
"virtual finger" at this position.

Moving the mouse moves another cursor. The left click may be released
and pressed as necessary to control the second finger.

Releasing Ctrl releases the virtual finger.

app/src/control_msg.h

@@ -16,6 +16,7 @@
     (3 + CONTROL_MSG_CLIPBOARD_TEXT_MAX_LENGTH)
 
 #define POINTER_ID_MOUSE UINT64_C(-1);
+#define POINTER_ID_VIRTUAL_FINGER UINT64_C(-2);
 
 enum control_msg_type {
     CONTROL_MSG_TYPE_INJECT_KEYCODE,

app/src/input_manager.c

@@ -7,6 +7,19 @@
 #include "lock_util.h"
 #include "log.h"
 
+void
+input_manager_init(struct input_manager *input_manager,
+                   struct controller *controller,
+                   struct video_buffer *video_buffer,
+                   struct screen *screen) {
+    input_manager->controller = controller;
+    input_manager->video_buffer = video_buffer;
+    input_manager->screen = screen;
+
+    input_manager->ctrl_down = false;
+    input_manager->vfinger.down = false;
+}
+
 // Convert window coordinates (as provided by SDL_GetMouseState() to renderer
 // coordinates (as provided in SDL mouse events)
 //
@@ -211,6 +224,26 @@ clipboard_paste(struct controller *controller) {
     }
 }
 
+static void
+simulate_virtual_finger(struct input_manager *input_manager, bool down,
+                        struct position *position) {
+    SDL_assert(input_manager->vfinger.down != down);
+    input_manager->vfinger.down = down;
+
+    struct control_msg msg;
+    msg.type = CONTROL_MSG_TYPE_INJECT_TOUCH_EVENT;
+    msg.inject_touch_event.action = down ? AMOTION_EVENT_ACTION_DOWN
+                                         : AMOTION_EVENT_ACTION_UP;
+    msg.inject_touch_event.pointer_id = POINTER_ID_VIRTUAL_FINGER;
+    msg.inject_touch_event.position = *position;
+    msg.inject_touch_event.pressure = 1.f;
+    msg.inject_touch_event.buttons = 0;
+
+    if (!controller_push_msg(input_manager->controller, &msg)) {
+        LOGW("Could not request 'inject virtual finger event'");
+    }
+}
+
 void
 input_manager_process_text_input(struct input_manager *input_manager,
                                  const SDL_TextInputEvent *event) {
@@ -244,6 +277,14 @@ input_manager_process_key(struct input_manager *input_manager,
     bool alt = event->keysym.mod & (KMOD_LALT | KMOD_RALT);
     bool meta = event->keysym.mod & (KMOD_LGUI | KMOD_RGUI);
 
+    // store the Ctrl state to modify mouse events
+    input_manager->ctrl_down = ctrl;
+
+    if (input_manager->vfinger.down && !ctrl) {
+        simulate_virtual_finger(input_manager, false,
+                                &input_manager->vfinger.position);
+    }
+
     // use Cmd on macOS, Ctrl on other platforms
 #ifdef __APPLE__
     bool cmd = !ctrl && meta;
@@ -427,6 +468,7 @@ input_manager_process_mouse_button(struct input_manager *input_manager,
         // simulated from touch events, so it's a duplicate
         return;
     }
+
     if (event->type == SDL_MOUSEBUTTONDOWN) {
         if (control && event->button == SDL_BUTTON_RIGHT) {
             press_back_or_turn_screen_on(input_manager->controller);
@@ -437,12 +479,24 @@ input_manager_process_mouse_button(struct input_manager *input_manager,
             return;
         }
         // double-click on black borders resize to fit the device screen
-        if (event->button == SDL_BUTTON_LEFT && event->clicks == 2) {
-            bool outside =
-                is_outside_device_screen(input_manager, event->x, event->y);
-            if (outside) {
-                screen_resize_to_fit(input_manager->screen);
-                return;
+        if (event->button == SDL_BUTTON_LEFT) {
+            if (event->clicks >= 2) {
+                bool outside =
+                    is_outside_device_screen(input_manager, event->x, event->y);
+                if (outside) {
+                    screen_resize_to_fit(input_manager->screen);
+                    return;
+                }
+            }
+
+            struct virtual_finger *vfinger = &input_manager->vfinger;
+            if (input_manager->ctrl_down && !vfinger->down) {
+                vfinger->position.point.x = event->x;
+                vfinger->position.point.y = event->y;
+                vfinger->position.screen_size =
+                    input_manager->screen->frame_size,
+                simulate_virtual_finger(input_manager, true,
+                                        &vfinger->position);
             }
         }
         // otherwise, send the click event to the device

app/src/input_manager.h

@@ -14,8 +14,21 @@ struct input_manager {
     struct controller *controller;
     struct video_buffer *video_buffer;
     struct screen *screen;
+
+    bool ctrl_down;
+
+    struct virtual_finger {
+        bool down;
+        struct position position;
+    } vfinger;
 };
 
+void
+input_manager_init(struct input_manager *input_manager,
+                   struct controller *controller,
+                   struct video_buffer *video_buffer,
+                   struct screen *screen);
+
 void
 input_manager_process_text_input(struct input_manager *input_manager,
                                  const SDL_TextInputEvent *event);

app/src/scrcpy.c

@@ -37,12 +37,7 @@ static struct decoder decoder;
 static struct recorder recorder;
 static struct controller controller;
 static struct file_handler file_handler;
-
-static struct input_manager input_manager = {
-    .controller = &controller,
-    .video_buffer = &video_buffer,
-    .screen = &screen,
-};
+static struct input_manager input_manager;
 
 // init SDL and set appropriate hints
 static bool
@@ -311,6 +306,8 @@ scrcpy(const struct scrcpy_options *options) {
         goto end;
     }
 
+    input_manager_init(&input_manager, &controller, &video_buffer, &screen);
+
     if (!server_connect_to(&server)) {
         goto end;
     }