From 4b6b0764c11b0a7e4d91ab2a52900f000fff5947 Mon Sep 17 00:00:00 2001
From: tmyqlfpir <80724828+tmyqlfpir@users.noreply.github.com>
Date: Wed, 18 Dec 2024 00:07:37 +1000
Subject: [PATCH] Blood: Fix interpolated sprite pos for ror transitions

---
 source/blood/src/view.h   | 16 ++++++++++++++++
 source/blood/src/warp.cpp | 12 ++++++++++--
 2 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/source/blood/src/view.h b/source/blood/src/view.h
index ac2ea068ea..681422ef47 100644
--- a/source/blood/src/view.h
+++ b/source/blood/src/view.h
@@ -202,3 +202,19 @@ inline void viewBackupSpriteLoc(int nSprite, spritetype *pSprite)
         SetBitString(gInterpolateSprite, nSprite);
     }
 }
+
+inline void viewCorrectSpriteInterpolateOffsets(int nSprite, spritetype *pSprite, vec3_t const *oldpos)
+{
+    if (TestBitString(gInterpolateSprite, nSprite))
+    {
+        if (!gViewInterpolate) // view interpolation is off, clear interpolation flag
+        {
+            ClearBitString(gInterpolateSprite, nSprite);
+            return;
+        }
+        LOCATION *pPrevLoc = &gPrevSpriteLoc[nSprite];
+        pPrevLoc->x = pSprite->x+(pPrevLoc->x-oldpos->x);
+        pPrevLoc->y = pSprite->y+(pPrevLoc->y-oldpos->y);
+        pPrevLoc->z = pSprite->z+(pPrevLoc->z-oldpos->z);
+    }
+}
diff --git a/source/blood/src/warp.cpp b/source/blood/src/warp.cpp
index b5d4c492f8..2ed17a7d19 100644
--- a/source/blood/src/warp.cpp
+++ b/source/blood/src/warp.cpp
@@ -200,6 +200,7 @@ int CheckLink(spritetype *pSprite)
             spritetype *pLower = &sprite[nLower];
             dassert(pLower->sectnum >= 0 && pLower->sectnum < kMaxSectors);
             ChangeSpriteSect(pSprite->index, pLower->sectnum);
+            vec3_t const oldpos = pSprite->xyz;
             pSprite->x += pLower->x-pUpper->x;
             pSprite->y += pLower->y-pUpper->y;
             int z2;
@@ -208,7 +209,10 @@ int CheckLink(spritetype *pSprite)
             else
                 z2 = getceilzofslope(pSprite->sectnum, pSprite->x, pSprite->y);
             pSprite->z += z2-z;
-            ClearBitString(gInterpolateSprite, pSprite->index);
+            if (!VanillaMode()) // if sprite is set to be interpolated, update previous position
+                viewCorrectSpriteInterpolateOffsets(pSprite->index, pSprite, &oldpos);
+            else
+                ClearBitString(gInterpolateSprite, pSprite->index);
             return pUpper->type;
         }
     }
@@ -227,6 +231,7 @@ int CheckLink(spritetype *pSprite)
             spritetype *pUpper = &sprite[nUpper];
             dassert(pUpper->sectnum >= 0 && pUpper->sectnum < kMaxSectors);
             ChangeSpriteSect(pSprite->index, pUpper->sectnum);
+            vec3_t const oldpos = pSprite->xyz;
             pSprite->x += pUpper->x-pLower->x;
             pSprite->y += pUpper->y-pLower->y;
             int z2;
@@ -235,7 +240,10 @@ int CheckLink(spritetype *pSprite)
             else
                 z2 = getflorzofslope(pSprite->sectnum, pSprite->x, pSprite->y);
             pSprite->z += z2-z;
-            ClearBitString(gInterpolateSprite, pSprite->index);
+            if (!VanillaMode()) // if sprite is set to be interpolated, update previous position
+                viewCorrectSpriteInterpolateOffsets(pSprite->index, pSprite, &oldpos);
+            else
+                ClearBitString(gInterpolateSprite, pSprite->index);
             return pLower->type;
         }
     }