vo_opengl_cb, vo_opengl: add option for preloading hwdec context

See manpage additions. This is mainly useful for vo_opengl_cb, but can
also be applied to vo_opengl.

On a side note, gl_hwdec_load_api() should stop using a name string, and
instead always use the IDs. This should be cleaned up another time.

DOCS/interface-changes.rst

@@ -20,6 +20,7 @@ Interface changes
 ::
 
  --- mpv 0.10.0 will be released ---
+    - add --hwdec-preload
     - add ao coreaudio exclusive suboption
     - add ``track-list/N/forced`` property
     - add audio-params/channel-count and ``audio-params-out/channel-count props.

DOCS/man/options.rst

@@ -579,6 +579,22 @@ Video
         codecs. See ``--hwdec-codecs`` to enable hardware decoding for more
         codecs.
 
+``--hwdec-preload=<api>``
+    This is useful for the ``opengl`` and ``opengl-cb`` VOs for creating the
+    hardware decoding OpenGL interop context, but without actually enabling
+    hardware decoding itself (like ``--hwdec`` does).
+
+    If set to ``no`` (default), the ``--hwdec`` option is used.
+
+    For ``opengl``, if set, do not create the interop context on demand, but
+    when the VO is created.
+
+    For ``opengl-cb``, if set, load the interop context as soon as the OpenGL
+    context is created. Since ``opengl-cb`` has no on-demand loading, this
+    allows enabling hardware decoding at runtime at all, without having to
+    to temporarily set the ``hwdec`` option just during OpenGL context
+    initialization with ``mpv_opengl_cb_init_gl()``.
+
 ``--panscan=<0.0-1.0>``
     Enables pan-and-scan functionality (cropping the sides of e.g. a 16:9
     video to make it fit a 4:3 display without black bands). The range

options/options.c

@@ -297,6 +297,7 @@ const m_option_t mp_opts[] = {
     OPT_FLAG("ad-spdif-dtshd", dtshd, 0),
 
     OPT_CHOICE_C("hwdec", hwdec_api, 0, mp_hwdec_names),
+    OPT_CHOICE_C("hwdec-preload", vo.hwdec_preload_api, 0, mp_hwdec_names),
     OPT_STRING("hwdec-codecs", hwdec_codecs, 0),
 
     OPT_SUBSTRUCT("sws", vo.sws_opts, sws_conf, 0),

options/options.h

@@ -42,7 +42,10 @@ typedef struct mp_vo_opts {
     float monitor_pixel_aspect;
     int force_window_position;
 
+    // vo_wayland, vo_drm
     struct sws_opts *sws_opts;
+    // vo_opengl, vo_opengl_cb
+    int hwdec_preload_api;
 } mp_vo_opts;
 
 struct mp_cache_opts {

video/out/gl_hwdec.c

@@ -86,6 +86,12 @@ struct gl_hwdec *gl_hwdec_load_api(struct mp_log *log, GL *gl,
     return NULL;
 }
 
+// Like gl_hwdec_load_api(), but use HWDEC_... identifiers.
+struct gl_hwdec *gl_hwdec_load_api_id(struct mp_log *log, GL *gl, int id)
+{
+    return gl_hwdec_load_api(log, gl, m_opt_choice_str(mp_hwdec_names, id));
+}
+
 void gl_hwdec_uninit(struct gl_hwdec *hwdec)
 {
     if (hwdec)

video/out/gl_hwdec.h

@@ -46,6 +46,7 @@ struct gl_hwdec_driver {
 
 struct gl_hwdec *gl_hwdec_load_api(struct mp_log *log, GL *gl,
                                    const char *api_name);
+struct gl_hwdec *gl_hwdec_load_api_id(struct mp_log *log, GL *gl, int id);
 
 void gl_hwdec_uninit(struct gl_hwdec *hwdec);
 

video/out/vo_opengl.c

@@ -440,6 +440,14 @@ static int preinit(struct vo *vo)
     p->hwdec_info.load_api = call_request_hwdec_api;
     p->hwdec_info.load_api_ctx = vo;
 
+    if (vo->opts->hwdec_preload_api != HWDEC_NONE) {
+        p->hwdec =
+            gl_hwdec_load_api_id(p->vo->log, p->gl, vo->opts->hwdec_preload_api);
+        gl_video_set_hwdec(p->renderer, p->hwdec);
+        if (p->hwdec)
+            p->hwdec_info.hwctx = p->hwdec->hwctx;
+    }
+
     return 0;
 
 err_out:

video/out/vo_opengl_cb.c

@@ -83,6 +83,8 @@ struct mpv_opengl_cb_context {
     int64_t recent_flip;
     int64_t approx_vsync;
     bool frozen; // libmpv user is not redrawing frames
+    struct vo *active;
+    int hwdec_api;
 
     // --- All of these can only be accessed from the thread where the host
     //     application's OpenGL context is current - i.e. only while the
@@ -91,12 +93,6 @@ struct mpv_opengl_cb_context {
     struct gl_video *renderer;
     struct gl_hwdec *hwdec;
     struct mp_hwdec_info hwdec_info; // it's also semi-immutable after init
-
-    // --- Immutable or semi-threadsafe.
-
-    const char *hwapi;
-
-    struct vo *active;
 };
 
 static void update(struct vo_priv *p);
@@ -194,13 +190,9 @@ struct mpv_opengl_cb_context *mp_opengl_create(struct mpv_global *g,
     ctx->log = mp_log_new(ctx, g->log, "opengl-cb");
     ctx->client_api = client_api;
 
-    switch (g->opts->hwdec_api) {
-    case HWDEC_AUTO:    ctx->hwapi = "auto"; break;
-    case HWDEC_VDPAU:   ctx->hwapi = "vdpau"; break;
-    case HWDEC_VDA:     ctx->hwapi = "vda"; break;
-    case HWDEC_VAAPI:   ctx->hwapi = "vaapi"; break;
-    default:            ctx->hwapi = "";
-    }
+    ctx->hwdec_api = g->opts->vo.hwdec_preload_api;
+    if (ctx->hwdec_api == HWDEC_NONE)
+        ctx->hwdec_api = g->opts->hwdec_api;
 
     return ctx;
 }
@@ -243,7 +235,7 @@ int mpv_opengl_cb_init_gl(struct mpv_opengl_cb_context *ctx, const char *exts,
     if (!ctx->renderer)
         return MPV_ERROR_UNSUPPORTED;
 
-    ctx->hwdec = gl_hwdec_load_api(ctx->log, ctx->gl, ctx->hwapi);
+    ctx->hwdec = gl_hwdec_load_api_id(ctx->log, ctx->gl, ctx->hwdec_api);
     gl_video_set_hwdec(ctx->renderer, ctx->hwdec);
     if (ctx->hwdec)
         ctx->hwdec_info.hwctx = ctx->hwdec->hwctx;