steamcompmgr: Add tuneables for vblank red zone + decay rate

src/steamcompmgr.cpp

@@ -3477,6 +3477,14 @@ handle_property_notify(xwayland_ctx_t *ctx, XPropertyEvent *ev)
 			}
 		}
 	}
+	if ( ev->atom == ctx->atoms.gamescopeTuneableVBlankRedZone )
+	{
+		g_uVblankDrawBufferRedZoneNS = (uint64_t)get_prop( ctx, ctx->root, ctx->atoms.gamescopeTuneableVBlankRedZone, g_uDefaultVBlankRedZone );
+	}
+	if ( ev->atom == ctx->atoms.gamescopeTuneableRateOfDecay )
+	{
+		g_uVBlankRateOfDecayPercentage = (uint64_t)get_prop( ctx, ctx->root, ctx->atoms.gamescopeTuneableRateOfDecay, g_uDefaultVBlankRateOfDecayPercentage );
+	}
 }
 
 static int
@@ -4316,6 +4324,10 @@ void init_xwayland_ctx(gamescope_xwayland_server_t *xwayland_server)
 	ctx->atoms.gamescopeMouseFocusDisplay = XInternAtom(ctx->dpy, "GAMESCOPE_MOUSE_FOCUS_DISPLAY", false);
 	ctx->atoms.gamescopeKeyboardFocusDisplay = XInternAtom( ctx->dpy, "GAMESCOPE_KEYBOARD_FOCUS_DISPLAY", false );
 
+	// In nanoseconds...
+	ctx->atoms.gamescopeTuneableVBlankRedZone = XInternAtom( ctx->dpy, "GAMESCOPE_TUNEABLE_VBLANK_REDZONE", false );
+	ctx->atoms.gamescopeTuneableRateOfDecay = XInternAtom( ctx->dpy, "GAMESCOPE_TUNEABLE_VBLANK_RATE_OF_DECAY_PERCENTAGE", false );
+
 	ctx->root_width = DisplayWidth(ctx->dpy, ctx->scr);
 	ctx->root_height = DisplayHeight(ctx->dpy, ctx->scr);
 

src/vblankmanager.cpp

@@ -27,17 +27,18 @@ const uint64_t g_uStartingDrawTime = 3'000'000;
 std::atomic<uint64_t> g_uVblankDrawTimeNS = { g_uStartingDrawTime };
 
 // Tuneable
-// 2.0ms
+// 2.0ms by default. (g_DefaultVBlankRedZone)
 // This is the leeway we always apply to our buffer.
 // This also accounts for some time we cannot account for (which (I think) is the drm_commit -> triggering the pageflip)
 // It would be nice to make this lower if we can find a way to track that effectively
 // Perhaps the missing time is spent elsewhere, but given we track from the pipe write
 // to after the return from `drm_commit` -- I am very doubtful.
-uint64_t g_uVblankDrawBufferRedZoneNS = 2'000'000;
+uint64_t g_uVblankDrawBufferRedZoneNS = g_uDefaultVBlankRedZone;
 
 // Tuneable
+// 93% by default. (g_uVBlankRateOfDecayPercentage)
 // The rate of decay (as a percentage) of the rolling average -> current draw time
-uint64_t g_uVBlankRateOfDecayPercentage = 93;
+uint64_t g_uVBlankRateOfDecayPercentage = g_uDefaultVBlankRateOfDecayPercentage;
 
 const uint64_t g_uVBlankRateOfDecayMax = 100;
 

src/vblankmanager.hpp

@@ -5,3 +5,9 @@ int vblank_init( void );
 void vblank_mark_possible_vblank( uint64_t nanos );
 
 extern std::atomic<uint64_t> g_uVblankDrawTimeNS;
+
+const unsigned int g_uDefaultVBlankRedZone = 2'000'000;
+const unsigned int g_uDefaultVBlankRateOfDecayPercentage = 93;
+
+extern uint64_t g_uVblankDrawBufferRedZoneNS;
+extern uint64_t g_uVBlankRateOfDecayPercentage;

src/xwayland_ctx.hpp

@@ -109,5 +109,8 @@ struct xwayland_ctx_t
 		Atom gamescopeFocusDisplay;
 		Atom gamescopeMouseFocusDisplay;
 		Atom gamescopeKeyboardFocusDisplay;
+
+		Atom gamescopeTuneableVBlankRedZone;
+		Atom gamescopeTuneableRateOfDecay;
 	} atoms;
 };