World: add skybox changer

New Visuals -> Skybox card with a runtime sv_skyname override using the same
mechanism as the stock skybox_swapper entity. The choice list is the HL2
skybox set extracted from the game VPKs.

The map's own sky is captured from loaded materials (SkyBox group, parsing
skybox/<name>... face names) before the first override, so turning the
feature off or picking "Map default" restores it; a level change restores it
implicitly. Sky changes invalidate the world tint so new sky materials are
tinted as well.

GUI: add a CK_CHOICE control (value box with < / > zones).

1 files changed, 1 insertions, 0 deletions

diff --git a/src/hl2h.cpp b/src/hl2h.cpp
index 3f1acb4..4ba1af3 100644
--- a/src/hl2h.cpp
+++ b/src/hl2h.cpp
@@ -592,6 +592,7 @@ static void do_move(int seq, float frametime) {
     fullbright_invalidate();
     world_tint_invalidate();
     fog_invalidate();
+    skybox_invalidate();
   }
 
   if (feature_active(FEAT_SPREAD)) {