SCI: Improve audio volume & settings sync code

This patch includes enhancements to the ScummVM integration with
SCI engine, with particular focus on SCI32 support.

1. Fixes audio volumes syncing erroneously to ScummVM in games
   that modify the audio volume without user action (e.g. SCI1.1
   talkies that reduce music volume during speech playback). Now,
   volumes will only be synchronised when the user interacts with
   the game's audio settings. This mechanism works by looking for
   a known volume control object in the stack, and only syncing
   when the control object is present. (Ports and planes were
   researched and found unreliable.)

2. Fixes audio syncing in SCI32 games that do not set game
   volumes through kDoSoundMasterVolume/kDoAudioVolume, like GK1,
   GK2, Phant1, and Torin.

3. Fixes speech/subtitles syncing in SCI32 games that do not use
   global 90, like LSL6hires.

4. Fixes in-game volume controls in SCI32 games reflecting
   outdated audio volumes when a change is made during the game
   from the ScummVM launcher.

5. Fixes SCI32 games that would restore volumes from save games
   or reset volumes on startup, which caused game volumes to be
   out-of-sync with ScummVM when started.

6. ScummVM integration code for audio sync has been abstracted
   into a new GuestAdditions class. This keeps the ScummVM-
   specific code all in one place, with only small hooks into the
   engine code. ScummVM integrated save/load code should probably
   also go here in the future.

Fixes Trac#9700.

1 files changed, 14 insertions, 0 deletions

diff --git a/engines/sci/engine/selector.h b/engines/sci/engine/selector.h
index 8d1edeb489..d8c0bf711b 100644
--- a/engines/sci/engine/selector.h
+++ b/engines/sci/engine/selector.h
@@ -158,6 +158,20 @@ struct SelectorCache {
 	Selector magnifier;
 	Selector frameOut;
 	Selector casts; // needed for sync'ing screen items/planes with scripts, when our save/restore code is patched in (see GfxFrameout::syncWithScripts)
+	Selector setVol; // for GK2 volume sync on restore
+	Selector reSyncVol; // for Torin volume sync on restore
+	Selector set; // for LSL6hires subtitle sync
+	Selector clear; // for LSL6hires subtitle sync
+	Selector curPos; // for LSL6hires volume sync
+	Selector update; // for LSL6hires volume sync
+	Selector show; // for GK1 volume sync
+	Selector position; // for GK1 volume sync
+	Selector musicVolume; // for GK1 volume sync
+	Selector soundVolume; // for GK1 volume sync
+	Selector initialOff; // for GK2 volume sync
+	Selector setPos; // for Torin volume sync
+	Selector setSize; // for PQ4 volume sync
+	Selector displayValue; // for PQ:SWAT volume sync
 #endif
 };