From 2d8c10a694cf124f5c44d9a6c482b7eaa19d8abb Mon Sep 17 00:00:00 2001
From: luigi budd <4997-luigi-budd@users.noreply.git.do.srb2.org>
Date: Sat, 10 May 2025 21:33:06 +0000
Subject: [PATCH] Interpolate hitlag jitters

---
 src/hardware/hw_main.c | 16 ++++++++++++----
 src/hardware/hw_md2.c  |  5 ++++-
 src/k_hitlag.h         |  1 +
 src/k_hud.cpp          |  6 +++++-
 src/r_things.cpp       | 11 ++++++++---
 5 files changed, 30 insertions(+), 9 deletions(-)

diff --git a/src/hardware/hw_main.c b/src/hardware/hw_main.c
index a9a90fbed..de43b9958 100644
--- a/src/hardware/hw_main.c
+++ b/src/hardware/hw_main.c
@@ -3115,11 +3115,15 @@ static void HWR_DrawDropShadow(mobj_t *thing, fixed_t scale)
 		R_InterpolateMobjState(thing, FRACUNIT, &interp);
 	}
 
-	// hitlag vibrating (todo: interp somehow?)
+	// hitlag vibrating
 	if (thing->hitlag > 0 && (thing->eflags & MFE_DAMAGEHITLAG))
 	{
-		fixed_t mul = thing->hitlag * HITLAGJITTERS;
+		fixed_t jitters = HITLAGJITTERS;
+		if (R_UsingFrameInterpolation() && !paused)
+			jitters += (rendertimefrac / HITLAGDIV);
+		fixed_t mul = thing->hitlag * jitters;
 
+		// perhaps there could be a way to interp this too?
 		if (leveltime & 1)
 		{
 			mul = -mul;
@@ -4685,10 +4689,14 @@ static void HWR_ProjectSprite(mobj_t *thing)
 
 	dispoffset = thing->dispoffset;
 
-	// hitlag vibrating (todo: interp somehow?)
+	// hitlag vibrating
 	if (thing->hitlag > 0 && (thing->eflags & MFE_DAMAGEHITLAG))
 	{
-		fixed_t mul = thing->hitlag * HITLAGJITTERS;
+		fixed_t jitters = HITLAGJITTERS;
+		if (R_UsingFrameInterpolation() && !paused)
+			jitters += (rendertimefrac / HITLAGDIV);
+			
+		fixed_t mul = thing->hitlag * jitters;
 
 		if (leveltime & 1)
 		{
diff --git a/src/hardware/hw_md2.c b/src/hardware/hw_md2.c
index 7a49edcb8..07dc450ef 100644
--- a/src/hardware/hw_md2.c
+++ b/src/hardware/hw_md2.c
@@ -1402,7 +1402,10 @@ boolean HWR_DrawModel(gl_vissprite_t *spr)
 		// hitlag vibrating
 		if (spr->mobj->hitlag > 0 && (spr->mobj->eflags & MFE_DAMAGEHITLAG))
 		{
-			fixed_t mul = spr->mobj->hitlag * HITLAGJITTERS;
+			fixed_t jitters = HITLAGJITTERS;
+			if (R_UsingFrameInterpolation() && !paused)
+				jitters += (rendertimefrac / HITLAGDIV);
+			fixed_t mul = spr->mobj->hitlag * jitters;
 
 			if (leveltime & 1)
 			{
diff --git a/src/k_hitlag.h b/src/k_hitlag.h
index c5c0944d5..f999c2181 100644
--- a/src/k_hitlag.h
+++ b/src/k_hitlag.h
@@ -22,6 +22,7 @@ extern "C" {
 
 #define MAXHITLAGTICS (30)
 #define HITLAGJITTERS (FRACUNIT / 20)
+#define HITLAGDIV (20)	// define this so we arent using a magic number for interp
 #define NUM_HITLAG_STATES (9)
 #define NUM_HITLAG_SOUNDS (4)
 
diff --git a/src/k_hud.cpp b/src/k_hud.cpp
index 4e6adebaa..7eaa48447 100644
--- a/src/k_hud.cpp
+++ b/src/k_hud.cpp
@@ -5317,7 +5317,11 @@ static void K_drawKartFirstPerson(void)
 		// hitlag vibrating
 		if (stplyr->mo->hitlag > 0 && (stplyr->mo->eflags & MFE_DAMAGEHITLAG))
 		{
-			fixed_t mul = stplyr->mo->hitlag * HITLAGJITTERS;
+			fixed_t jitters = HITLAGJITTERS;
+			if (R_UsingFrameInterpolation() && !paused)
+				jitters += (rendertimefrac / HITLAGDIV);
+			
+			fixed_t mul = stplyr->mo->hitlag * jitters;
 			if (r_splitscreen && mul > FRACUNIT)
 				mul = FRACUNIT;
 
diff --git a/src/r_things.cpp b/src/r_things.cpp
index ac23b679c..e48bb9b15 100644
--- a/src/r_things.cpp
+++ b/src/r_things.cpp
@@ -1794,7 +1794,7 @@ static void R_ProjectSprite(mobj_t *thing)
 
 	this_scale = interp.scale;
 
-	// hitlag vibrating (todo: interp somehow?)
+	// hitlag vibrating
 	if (thing->hitlag > 0 && (thing->eflags & MFE_DAMAGEHITLAG))
 	{
 		fixed_t mul = thing->hitlag * HITLAGJITTERS;
@@ -2172,10 +2172,15 @@ static void R_ProjectSprite(mobj_t *thing)
 			R_InterpolateMobjState(thing, FRACUNIT, &tracer_interp);
 		}
 
-		// hitlag vibrating (todo: interp somehow?)
+		// hitlag vibrating
 		if (thing->hitlag > 0 && (thing->eflags & MFE_DAMAGEHITLAG))
 		{
-			fixed_t mul = thing->hitlag * (FRACUNIT / 10);
+			// previous code multiplied by (FRACUNIT / 10) instead of HITLAGJITTERS, um wadaflip
+			fixed_t jitters = HITLAGJITTERS;
+			if (R_UsingFrameInterpolation() && !paused)
+				jitters += (rendertimefrac / HITLAGDIV);
+			
+			fixed_t mul = thing->hitlag * jitters;
 
 			if (leveltime & 1)
 			{