Added INTERPOLATE actor flag, allowing the previously reverted interpolation code to be toggleable.

src/actor.h

@@ -424,6 +424,7 @@ enum ActorRenderFlag
 	RF_MASKROTATION		= 0x00200000, // [MC] Only draw the actor when viewed from a certain angle range.
 	RF_ABSMASKANGLE		= 0x00400000, // [MC] The mask rotation does not offset by the actor's angle.
 	RF_ABSMASKPITCH		= 0x00800000, // [MC] The mask rotation does not offset by the actor's pitch.
+	RF_INTERPOLATE		= 0x01000000, // [MC] Allow interpolation of the actor's angle, pitch and roll.
 
 	RF_FORCEYBILLBOARD		= 0x10000,	// [BB] OpenGL only: draw with y axis billboard, i.e. anchored to the floor (overrides gl_billboard_mode setting)
 	RF_FORCEXYBILLBOARD		= 0x20000,	// [BB] OpenGL only: draw with xy axis billboard, i.e. unanchored (overrides gl_billboard_mode setting)

src/gl/scene/gl_sprite.cpp

@@ -737,8 +737,11 @@ void GLSprite::Process(AActor* thing, sector_t * sector, int thruportal)
 		int clipres = GLRenderer->mClipPortal->ClipPoint(thingpos);
 		if (clipres == GLPortal::PClip_InFront) return;
 	}
-	// disabled because almost none of the actual game code is even remotely prepared for this. Sorry for the few cases where it may be desired, but the overall effect is too bad.
+	// disabled because almost none of the actual game code is even remotely prepared for this. If desired, use the INTERPOLATE flag.
-	Angles = thing->Angles;// InterpolatedAngles(r_TicFracF);
+	if (thing->renderflags & RF_INTERPOLATE)
+		Angles = thing->InterpolatedAngles(r_TicFracF);
+	else
+		Angles = thing->Angles;
 
 	player_t *player = &players[consoleplayer];
 	FloatRect r;

src/scripting/thingdef_data.cpp

@@ -326,6 +326,7 @@ static FFlagDef ActorFlagDefs[]=
 	DEFINE_FLAG(RF, ABSMASKPITCH, AActor, renderflags),
 	DEFINE_FLAG(RF, XFLIP, AActor, renderflags),
 	DEFINE_FLAG(RF, YFLIP, AActor, renderflags),
+	DEFINE_FLAG(RF, INTERPOLATE, AActor, renderflags),
 
 	// Bounce flags
 	DEFINE_FLAG2(BOUNCE_Walls, BOUNCEONWALLS, AActor, BounceFlags),