sdvx: option to disable Live2D (#777)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Adds an option to disable Live2D. Can be disabled everywhere, or just
during a song.

## Testing
Tested EG final and recent Nabla.

src/spice2x/launcher/launcher.cpp

@@ -53,6 +53,7 @@
 #include "games/sc/sc.h"
 #include "games/scotto/scotto.h"
 #include "games/sdvx/sdvx.h"
+#include "games/sdvx/sdvx_live2d.h"
 #include "games/shared/printer.h"
 #include "games/silentscope/silentscope.h"
 #include "games/mfc/mfc.h"
@@ -1046,6 +1047,20 @@ int main_implementation(int argc, char *argv[]) {
     if (options[launcher::Options::SDVXForce720p].value_bool()) {
         GRAPHICS_SDVX_FORCE_720 = true;
     }
+#ifdef SPICE64
+    // only the Live2D-capable SDVX versions are 64-bit, so this whole feature is
+    // gated out of 32-bit builds and only armed for SDVX (model KFC).
+    if (avs::game::is_model("KFC")) {
+        auto live2d = options[launcher::Options::SDVXDisableLive2D].value_text();
+        if (live2d == "always") {
+            GRAPHICS_SDVX_LIVE2D_MODE = SdvxLive2dMode::Always;
+        } else if (live2d == "ingame") {
+            GRAPHICS_SDVX_LIVE2D_MODE = SdvxLive2dMode::InGame;
+            // scene detection runs independently of the SDVX game module
+            games::sdvx::live2d_scene_detection_init();
+        }
+    }
+#endif // SPICE64
     if (options[launcher::Options::InvertTouchCoordinates].value_bool()) {
         rawinput::touch::INVERTED = true;
     }

src/spice2x/launcher/options.cpp

@@ -1026,6 +1026,24 @@ static const std::vector<OptionDefinition> OPTION_DEFINITIONS = {
         .category = "Game Options",
         .quick_setting_category = "Game",
     },
+    {
+        // SDVXDisableLive2D
+        .title = "SDVX Disable Live2D (EXPERIMENTAL)",
+        .name = "sdvxnolive2d",
+        .desc = "Skip rendering the SDVX Live2D graphics to save GPU.\n\n"
+                "Off: leave Live2D as-is.\n"
+                "Always: never render Live2D (also removes the menu navigator).\n"
+                "During songs: only skip Live2D during a song; keeps the menu navigator. Scene detection relies on game logging.",
+        .type = OptionType::Enum,
+        .game_name = "Sound Voltex",
+        .category = "Advanced Game Options",
+        .elements = {
+            {"off", "Show Live2D"},
+            {"always", "Never show Live2D"},
+            {"ingame", "Show navigators only"},
+        },
+        .quick_setting_category = "Game",
+    },
     {
         // spice2x_SDVXSubPos
         .title = "SDVX Subscreen Overlay Position",

src/spice2x/launcher/options.h

@@ -97,6 +97,7 @@ namespace launcher {
             SDVXDigitalKnobSocd,
             spice2x_SDVXAsioDriver,
             SDVXAsioTwoChannel,
+            SDVXDisableLive2D,
             spice2x_SDVXSubPos,
             SDVXSubMonitorOverride,
             LoadDDRModule,