From bf9a63b0900cb31d62c9188a5e952defdd6efa91 Mon Sep 17 00:00:00 2001
From: Roman Fomin <rfomin@gmail.com>
Date: Wed, 25 May 2022 17:42:59 +0700
Subject: [PATCH] fix weapon bobbing interpolation at the start of the level

---
 Source/r_things.c | 27 ++++++++++++++++-----------
 1 file changed, 16 insertions(+), 11 deletions(-)

diff --git a/Source/r_things.c b/Source/r_things.c
index f4724ed6..3e0ea2fa 100644
--- a/Source/r_things.c
+++ b/Source/r_things.c
@@ -777,18 +777,23 @@ void R_DrawPSprite (pspdef_t *psp)
     x1_saved = vis->x1;
     texturemid_saved = vis->texturemid;
 
-    if (lump == oldlump)
+    // Do not interpolate on the first tic of the level,
+    // otherwise oldx1 and oldtexturemid are not reset
+    if (leveltime > 1)
     {
-      int deltax = vis->x2 - vis->x1;
-      vis->x1 = oldx1 + FixedMul(vis->x1 - oldx1, fractionaltic);
-      vis->x2 = vis->x1 + deltax;
-      vis->texturemid = oldtexturemid + FixedMul(vis->texturemid - oldtexturemid, fractionaltic);
-    }
-    else
-    {
-      oldx1 = vis->x1;
-      oldtexturemid = vis->texturemid;
-      oldlump = lump;
+      if (lump == oldlump)
+      {
+        int deltax = vis->x2 - vis->x1;
+        vis->x1 = oldx1 + FixedMul(vis->x1 - oldx1, fractionaltic);
+        vis->x2 = vis->x1 + deltax;
+        vis->texturemid = oldtexturemid + FixedMul(vis->texturemid - oldtexturemid, fractionaltic);
+      }
+      else
+      {
+        oldx1 = vis->x1;
+        oldtexturemid = vis->texturemid;
+        oldlump = lump;
+      }
     }
   }