From 6b7065899da294ecd477e97b45be1ad2105b105a Mon Sep 17 00:00:00 2001
From: Boondorl <boondorl@live.com>
Date: Fri, 1 Mar 2024 11:15:17 -0500
Subject: [PATCH] Added interpolation to view position

---
 src/playsim/d_player.h             |  1 +
 src/playsim/p_user.cpp             |  1 +
 src/rendering/r_utility.cpp        | 32 +++++++++++++++++++++---------
 wadsrc/static/zscript/constants.zs |  1 +
 4 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/src/playsim/d_player.h b/src/playsim/d_player.h
index 49d8d54a1f..34ac55da6f 100644
--- a/src/playsim/d_player.h
+++ b/src/playsim/d_player.h
@@ -125,6 +125,7 @@ typedef enum
 	CF_INTERPVIEWANGLES	= 1 << 15,		// [MR] flag for interpolating view angles without interpolating the entire frame
 	CF_NOFOVINTERP		= 1 << 16,		// [B] Disable FOV interpolation when instantly zooming
 	CF_SCALEDNOLERP		= 1 << 17,		// [MR] flag for applying angles changes in the ticrate without interpolating the frame
+	CF_NOVIEWPOSINTERP	= 1 << 18,		// Disable view position interpolation.
 	CF_EXTREMELYDEAD	= 1 << 22,		// [RH] Reliably let the status bar know about extreme deaths.
 	CF_BUDDHA2			= 1 << 24,		// [MC] Absolute buddha. No voodoo can kill it either.
 	CF_GODMODE2			= 1 << 25,		// [MC] Absolute godmode. No voodoo can kill it either.
diff --git a/src/playsim/p_user.cpp b/src/playsim/p_user.cpp
index a1888d5c15..6839b412ac 100644
--- a/src/playsim/p_user.cpp
+++ b/src/playsim/p_user.cpp
@@ -1278,6 +1278,7 @@ void P_PlayerThink (player_t *player)
 	player->cheats &= ~CF_INTERPVIEWANGLES;
 	player->cheats &= ~CF_SCALEDNOLERP;
 	player->cheats &= ~CF_NOFOVINTERP;
+	player->cheats &= ~CF_NOVIEWPOSINTERP;
 	player->mo->FloatVar("prevBob") = player->bob;
 
 	IFVIRTUALPTRNAME(player->mo, NAME_PlayerPawn, PlayerThink)
diff --git a/src/rendering/r_utility.cpp b/src/rendering/r_utility.cpp
index fbb785d0b5..b78cf955d0 100644
--- a/src/rendering/r_utility.cpp
+++ b/src/rendering/r_utility.cpp
@@ -78,7 +78,7 @@ struct InterpolationViewer
 {
 	struct instance
 	{
-		DVector3 Pos;
+		DVector3 Pos, ViewPos;
 		DRotator Angles;
 		DRotator ViewAngles;
 	};
@@ -605,6 +605,22 @@ void R_InterpolateView(FRenderViewpoint& viewPoint, const player_t* const player
 
 	// Now that the base position and angles are set, add offsets.
 
+	const DViewPosition* const vPos = iView->ViewActor->ViewPos;
+	if (vPos != nullptr && !(vPos->Flags & VPSF_ABSOLUTEPOS)
+		&& (player == nullptr || gamestate == GS_TITLELEVEL || (!(player->cheats & CF_CHASECAM) && (!r_deathcamera || !(iView->ViewActor->flags6 & MF6_KILLED)))))
+	{
+		DVector3 vOfs = {};
+		if (player == nullptr || !(player->cheats & CF_NOVIEWPOSINTERP))
+			vOfs = iView->Old.ViewPos * inverseTicFrac + iView->New.ViewPos * ticFrac;
+		else
+			vOfs = iView->New.ViewPos;
+
+		if (vPos->Flags & VPSF_ABSOLUTEOFFSET)
+			iView->ViewOffset += vOfs;
+		else
+			iView->RelativeViewOffset += vOfs;
+	}
+
 	DVector3 posOfs = iView->ViewOffset;
 	if (!iView->RelativeViewOffset.isZero())
 		posOfs += DQuaternion::FromAngles(viewPoint.Angles.Yaw, viewPoint.Angles.Pitch, viewPoint.Angles.Roll) * iView->RelativeViewOffset;
@@ -916,8 +932,8 @@ void R_SetupFrame(FRenderViewpoint& viewPoint, const FViewWindow& viewWindow, AA
 		viewPoint.showviewer = false;
 		viewPoint.bForceNoViewer = matchPlayer;
 
-		if (gamestate != GS_TITLELEVEL &&
-			((player != nullptr && (player->cheats & CF_CHASECAM)) || (r_deathcamera && (viewPoint.camera->flags6 & MF6_KILLED))))
+		if (player != nullptr && gamestate != GS_TITLELEVEL
+			&& ((player->cheats & CF_CHASECAM) || (r_deathcamera && (viewPoint.camera->flags6 & MF6_KILLED))))
 		{
 			// The cam Actor should probably be visible in third person.
 			viewPoint.showviewer = true;
@@ -925,7 +941,8 @@ void R_SetupFrame(FRenderViewpoint& viewPoint, const FViewWindow& viewWindow, AA
 			iView->ViewOffset.Z = clamp<double>(chase_height, -1000.0, 1000.0);
 			iView->RelativeViewOffset.X = -clamp<double>(chase_dist, 0.0, 30000.0);
 		}
-		else if (viewOffset != nullptr)
+
+		if (viewOffset != nullptr)
 		{
 			// No chase/death cam, so use the view offset.
 			if (!viewPoint.bForceNoViewer)
@@ -933,16 +950,13 @@ void R_SetupFrame(FRenderViewpoint& viewPoint, const FViewWindow& viewWindow, AA
 			
 			if (viewOffset->Flags & VPSF_ABSOLUTEPOS)
 			{
+				iView->New.ViewPos.Zero();
 				if (!matchPlayer)
 					camPos = viewOffset->Offset;
 			}
-			else if (viewOffset->Flags & VPSF_ABSOLUTEOFFSET)
-			{
-				iView->ViewOffset += viewOffset->Offset;
-			}
 			else
 			{
-				iView->RelativeViewOffset = viewOffset->Offset;
+				iView->New.ViewPos = viewOffset->Offset;
 			}
 		}
 
diff --git a/wadsrc/static/zscript/constants.zs b/wadsrc/static/zscript/constants.zs
index 7afacf2086..92120c36df 100644
--- a/wadsrc/static/zscript/constants.zs
+++ b/wadsrc/static/zscript/constants.zs
@@ -1161,6 +1161,7 @@ enum EPlayerCheats
 	CF_INTERPVIEWANGLES	= 1 << 15,		// [MR] flag for interpolating view angles without interpolating the entire frame
 	CF_NOFOVINTERP		= 1 << 16,		// [B] Disable FOV interpolation when instantly zooming
 	CF_SCALEDNOLERP		= 1 << 17,		// [MR] flag for applying angles changes in the ticrate without interpolating the frame
+	CF_NOVIEWPOSINTERP	= 1 << 18,		// Disable view position interpolation.
 
 	CF_EXTREMELYDEAD	= 1 << 22,		// [RH] Reliably let the status bar know about extreme deaths.