Add virtual display feature

Add a feature to create a new (separate) virtual display instead of
mirroring the device screen:

    scrcpy --new-display=1920x1080
    scrcpy --new-display=1920x1080/420  # force 420 dpi
    scrcpy --new-display       # use the default screen size and density
    scrcpy --new-display=/240  # use the default screen size and 240 dpi

Co-authored-by: Simon Chan <1330321+yume-chan@users.noreply.github.com>
Co-authored-by: anirudhb <anirudhb@users.noreply.github.com>

app/src/cli.c

@@ -102,6 +102,7 @@ enum {
     OPT_NO_MOUSE_HOVER,
     OPT_AUDIO_DUP,
     OPT_GAMEPAD,
+    OPT_NEW_DISPLAY,
 };
 
 struct sc_option {
@@ -557,6 +558,20 @@ static const struct sc_option options[] = {
         .text = "Disable video and audio playback on the computer (equivalent "
                 "to --no-video-playback --no-audio-playback).",
     },
+    {
+        .longopt_id = OPT_NEW_DISPLAY,
+        .longopt = "new-display",
+        .argdesc = "[<width>x<height>][/<dpi>]",
+        .optional_arg = true,
+        .text = "Create a new display with the specified resolution and "
+                "density. If not provided, they default to the main display "
+                "dimensions and DPI, and --max-size is considered.\n"
+                "Examples:\n"
+                "    --new-display=1920x1080\n"
+                "    --new-display=1920x1080/420  # force 420 dpi\n"
+                "    --new-display       # default screen size and density\n"
+                "    --new-display=240   # default screen size and 240 dpi",
+    },
     {
         .longopt_id = OPT_NO_AUDIO,
         .longopt = "no-audio",
@@ -2668,6 +2683,9 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
                     return false;
                 }
                 break;
+            case OPT_NEW_DISPLAY:
+                opts->new_display = optarg ? optarg : "auto";
+                break;
             default:
                 // getopt prints the error message on stderr
                 return false;
@@ -2918,6 +2936,11 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
             return false;
         }
 
+        if (opts->new_display) {
+            LOGE("--new-display is only available with --video-source=display");
+            return false;
+        }
+
         if (opts->camera_id && opts->camera_facing != SC_CAMERA_FACING_ANY) {
             LOGE("Cannot specify both --camera-id and --camera-facing");
             return false;
@@ -2954,6 +2977,11 @@ parse_args_with_getopt(struct scrcpy_cli_args *args, int argc, char *argv[],
         return false;
     }
 
+    if (opts->display_id != 0 && opts->new_display) {
+        LOGE("Cannot specify both --display-id and --new-display");
+        return false;
+    }
+
     if (opts->audio && opts->audio_source == SC_AUDIO_SOURCE_AUTO) {
         // Select the audio source according to the video source
         if (opts->video_source == SC_VIDEO_SOURCE_DISPLAY) {

app/src/options.c

@@ -103,6 +103,7 @@ const struct scrcpy_options scrcpy_options_default = {
     .window = true,
     .mouse_hover = true,
     .audio_dup = false,
+    .new_display = NULL,
 };
 
 enum sc_orientation

app/src/options.h

@@ -308,6 +308,7 @@ struct scrcpy_options {
     bool window;
     bool mouse_hover;
     bool audio_dup;
+    const char *new_display; // [<width>x<height>][/<dpi>] parsed by the server
 };
 
 extern const struct scrcpy_options scrcpy_options_default;

app/src/scrcpy.c

@@ -431,6 +431,7 @@ scrcpy(struct scrcpy_options *options) {
         .lock_video_orientation = options->lock_video_orientation,
         .control = options->control,
         .display_id = options->display_id,
+        .new_display = options->new_display,
         .video = options->video,
         .audio = options->audio,
         .audio_dup = options->audio_dup,

app/src/server.c

@@ -355,6 +355,10 @@ execute_server(struct sc_server *server,
         // By default, power_on is true
         ADD_PARAM("power_on=false");
     }
+    if (params->new_display) {
+        VALIDATE_STRING(params->new_display);
+        ADD_PARAM("new_display=%s", params->new_display);
+    }
     if (params->list & SC_OPTION_LIST_ENCODERS) {
         ADD_PARAM("list_encoders=true");
     }

app/src/server.h

@@ -48,6 +48,7 @@ struct sc_server_params {
     int8_t lock_video_orientation;
     bool control;
     uint32_t display_id;
+    const char *new_display;
     bool video;
     bool audio;
     bool audio_dup;