screenshots: add --screenshot-directory option

The plan is to use this to change the screenshot default location in
pseudo-gui mode.

DOCS/man/options.rst

@@ -2656,6 +2656,17 @@ Screenshot
     ``%%``
         Replaced with the ``%`` character itself.
 
+``--screenshot-directory=<path>``
+    Store screenshots in this directory. This path is joined with the filename
+    generated by ``--screenshot-template``. If the template filename is already
+    absolute, the directory is ignored.
+
+    If the directory does not exist or is not a directory, an error is
+    generated.
+
+    This option is not set by default, and thus will write screenshots to the
+    directory from which mpv was started.
+
 ``--screenshot-jpeg-quality=<0-100>``
     Set the JPEG quality level. Higher means better quality. The default is 90.
 

options/options.c

@@ -543,6 +543,7 @@ const m_option_t mp_opts[] = {
 
     OPT_SUBSTRUCT("screenshot", screenshot_image_opts, image_writer_conf, 0),
     OPT_STRING("screenshot-template", screenshot_template, 0),
+    OPT_STRING("screenshot-directory", screenshot_direcrory, 0),
 
     OPT_SUBSTRUCT("input", input_opts, input_config, 0),
 

options/options.h

@@ -206,6 +206,7 @@ typedef struct MPOpts {
 
     struct image_writer_opts *screenshot_image_opts;
     char *screenshot_template;
+    char *screenshot_direcrory;
 
     double force_fps;
     int index_mode;

player/screenshot.c

@@ -280,6 +280,14 @@ static char *gen_fname(screenshot_ctx *ctx, const char *file_ext)
             return NULL;
         }
 
+        char *dir = ctx->mpctx->opts->screenshot_direcrory;
+        if (dir && dir[0]) {
+            void *t = fname;
+            dir = mp_get_user_path(t, ctx->mpctx->global, dir);
+            fname = mp_path_join(NULL, bstr0(dir), bstr0(fname));
+            talloc_free(t);
+        }
+
         if (!mp_path_exists(fname))
             return fname;