feat: LOAD command without parameters will put the background clip in…

…to the 'preview' state (same as doing a LOAD of it to begin with)

src/core/producer/layer.cpp

@@ -45,17 +45,23 @@ struct layer::impl
 
     void resume() { paused_ = false; }
 
-    void load(spl::shared_ptr<frame_producer> producer, bool preview, bool auto_play)
+    void load(spl::shared_ptr<frame_producer> producer, bool preview_producer, bool auto_play)
     {
         background_ = std::move(producer);
         auto_play_  = auto_play;
 
         if (auto_play_ && foreground_ == frame_producer::empty()) {
             play();
-        } else if (preview) {
-            foreground_ = std::move(background_);
-            background_ = frame_producer::empty();
-            paused_     = true;
+        } else if (preview_producer) {
+            preview(true);
+        }
+    }
+
+    void preview(bool force)
+    {
+        if (force || background_ != frame_producer::empty()) {
+            play();
+            paused_ = true;
         }
     }
 
@@ -160,6 +166,7 @@ void layer::load(spl::shared_ptr<frame_producer> frame_producer, bool preview, b
     return impl_->load(std::move(frame_producer), preview, auto_play);
 }
 void       layer::play() { impl_->play(); }
+void       layer::preview() { impl_->preview(false); }
 void       layer::pause() { impl_->pause(); }
 void       layer::resume() { impl_->resume(); }
 void       layer::stop() { impl_->stop(); }

src/core/producer/layer.h

@@ -45,6 +45,7 @@ class layer final
 
     void load(spl::shared_ptr<frame_producer> producer, bool preview, bool auto_play = false);
     void play();
+    void preview();
     void pause();
     void resume();
     void stop();

src/core/producer/stage.cpp

@@ -230,6 +230,11 @@ struct stage::impl : public std::enable_shared_from_this<impl>
     {
         return executor_.begin_invoke([=] { get_layer(index).load(producer, preview, auto_play); });
     }
+
+	std::future<void> preview(int index)
+    {
+        return executor_.begin_invoke([=] { get_layer(index).preview(); });
+    }
 
     std::future<void> pause(int index)
     {
@@ -369,6 +374,7 @@ std::future<void> stage::load(int index, const spl::shared_ptr<frame_producer>&
 {
     return impl_->load(index, producer, preview, auto_play);
 }
+std::future<void> stage::preview(int index) { return impl_->preview(index); }
 std::future<void> stage::pause(int index) { return impl_->pause(index); }
 std::future<void> stage::resume(int index) { return impl_->resume(index); }
 std::future<void> stage::play(int index) { return impl_->play(index); }

src/core/producer/stage.h

@@ -71,6 +71,7 @@ class stage final
     std::future<frame_transform> get_current_transform(int index);
     std::future<void>
                               load(int index, const spl::shared_ptr<frame_producer>& producer, bool preview = false, bool auto_play = false);
+    std::future<void>         preview(int index);
     std::future<void>         pause(int index);
     std::future<void>         resume(int index);
     std::future<void>         play(int index);

src/protocol/amcp/AMCPCommandsImpl.cpp

@@ -267,18 +267,23 @@ std::wstring load_command(command_context& ctx)
     core::diagnostics::call_context::for_thread().video_channel = ctx.channel_index + 1;
     core::diagnostics::call_context::for_thread().layer         = ctx.layer_index();
 
-    try {
-        auto pFP =
-            ctx.producer_registry->create_producer(get_producer_dependencies(ctx.channel.channel, ctx), ctx.parameters);
-        auto pFP2 = create_transition_producer(pFP, transition_info{});
-
-        ctx.channel.channel->stage().load(ctx.layer_index(), pFP2, true);
-    } catch (file_not_found&) {
-        if (contains_param(L"CLEAR_ON_404", ctx.parameters)) {
-            ctx.channel.channel->stage().load(
-                ctx.layer_index(), core::create_color_producer(ctx.channel.channel->frame_factory(), 0), true);
+    if (ctx.parameters.empty()) {
+        // Must be a promoting load
+        ctx.channel.channel->stage().preview(ctx.layer_index());
+    } else {
+        try {
+            auto pFP  = ctx.producer_registry->create_producer(get_producer_dependencies(ctx.channel.channel, ctx),
+                                                              ctx.parameters);
+            auto pFP2 = create_transition_producer(pFP, transition_info{});
+
+            ctx.channel.channel->stage().load(ctx.layer_index(), pFP2, true);
+        } catch (file_not_found&) {
+            if (contains_param(L"CLEAR_ON_404", ctx.parameters)) {
+                ctx.channel.channel->stage().load(
+                    ctx.layer_index(), core::create_color_producer(ctx.channel.channel->frame_factory(), 0), true);
+            }
+            throw;
         }
-        throw;
     }
 
     return L"202 LOAD OK\r\n";
@@ -1520,7 +1525,7 @@ std::wstring gl_gc_command(command_context& ctx)
 void register_commands(amcp_command_repository& repo)
 {
     repo.register_channel_command(L"Basic Commands", L"LOADBG", loadbg_command, 1);
-    repo.register_channel_command(L"Basic Commands", L"LOAD", load_command, 1);
+    repo.register_channel_command(L"Basic Commands", L"LOAD", load_command, 0);
     repo.register_channel_command(L"Basic Commands", L"PLAY", play_command, 0);
     repo.register_channel_command(L"Basic Commands", L"PAUSE", pause_command, 0);
     repo.register_channel_command(L"Basic Commands", L"RESUME", resume_command, 0);