Fix flip_levels in three-screen mode, and more

Also expanded explanation of the fix in the previous commit.

CHANGELOG.md

@@ -15,6 +15,8 @@
 
 - Broken movement in systems assuming `char`s to be unsigned
 - `comp_lsamnesia` inversely affecting collision with entities (i.e. lost souls would remember their target)
-- Weapon sprites being raised/lowered excessively when using switch interruption with certain bobbing styles
+- Weapon sprites being raised/lowered excessively when using switch interruption
+  with certain bobbing styles and/or reduced weapon bobbing amplitude
+- _Flip Levels_ setting not working for side screens in three-screen mode
 - Message grouping only checking as many characters as the last message had,
   causing incorrect grouping (e.g. new message "TEST" being grouped with last message "TES")

src/r_main.c

@@ -1280,6 +1280,10 @@ void R_SetupFrame (player_t *player)
 
   // [Nugget] /===============================================================
 
+  // Flip levels
+  if (viewangleoffset && STRICTMODE(flip_levels))
+  { viewangle += ANG180; }
+
   // Alt. intermission background --------------------------------------------
 
   if (WI_UsingAltInterpic() && gamestate == GS_INTERMISSION)

src/r_things.c

@@ -1024,23 +1024,6 @@ void R_DrawPlayerSprites(void)
   mfloorclip = screenheightarray;
   mceilingclip = negonearray;
 
-  // [Nugget] Flip levels
-  if (STRICTMODE(flip_levels))
-  {
-    for (int y = 0;  y < viewheight;  y++)
-    {
-      for (int x = 0;  x < viewwidth/2;  x++)
-      {
-        pixel_t *left = &I_VideoBuffer[(viewwindowy + y) * video.pitch + viewwindowx + x],
-                *right = left + viewwidth - 1 - x*2,
-                temp = *left;
-
-        *left = *right;
-        *right = temp;
-      }
-    }
-  }
-
   // display crosshair
   if (hud_crosshair_on) // [Nugget] Use crosshair toggle
     HU_DrawCrosshair();
@@ -1373,6 +1356,23 @@ void R_DrawMasked(void)
     if (ds->maskedtexturecol)
       R_RenderMaskedSegRange(ds, ds->x1, ds->x2);
 
+  // [Nugget] Flip levels
+  if (STRICTMODE(flip_levels))
+  {
+    for (int y = 0;  y < viewheight;  y++)
+    {
+      for (int x = 0;  x < viewwidth/2;  x++)
+      {
+        pixel_t *left = &I_VideoBuffer[(viewwindowy + y) * video.pitch + viewwindowx + x],
+                *right = left + viewwidth - 1 - x*2,
+                temp = *left;
+
+        *left = *right;
+        *right = temp;
+      }
+    }
+  }
+
   // draw the psprites on top of everything
   //  but does not draw on side views
   if (!viewangleoffset)