From bac12948e5f1a62b1820dc8d66e5fd1a8a503d8c Mon Sep 17 00:00:00 2001
From: Rachael Alexanderson <madame-rachelle@users.noreply.github.com>
Date: Sat, 14 Oct 2023 10:35:28 -0400
Subject: [PATCH] - add `forcecullbackfaces` in `modeldef`

---
 src/r_data/models.cpp                  |  4 ++++
 src/r_data/models.h                    | 29 +++++++++++++-------------
 src/rendering/hwrenderer/hw_models.cpp |  4 ++--
 3 files changed, 21 insertions(+), 16 deletions(-)

diff --git a/src/r_data/models.cpp b/src/r_data/models.cpp
index ab632b34f..85f646b41 100644
--- a/src/r_data/models.cpp
+++ b/src/r_data/models.cpp
@@ -931,6 +931,10 @@ static void ParseModelDefLump(int Lump)
 				{
 					smf.flags |= MDL_CORRECTPIXELSTRETCH;
 				}
+				else if (sc.Compare("forcecullbackfaces"))
+				{
+					smf.flags |= MDL_FORCECULLBACKFACES;
+				}
 				else
 				{
 					sc.ScriptMessage("Unrecognized string \"%s\"", sc.String);
diff --git a/src/r_data/models.h b/src/r_data/models.h
index 568ad5399..b80550ab2 100644
--- a/src/r_data/models.h
+++ b/src/r_data/models.h
@@ -45,20 +45,21 @@ enum
 {
 	// [BB] Color translations for the model skin are ignored. This is
 	// useful if the skin texture is not using the game palette.
-	MDL_IGNORETRANSLATION			= 1,
-	MDL_PITCHFROMMOMENTUM			= 2,
-	MDL_ROTATING					= 4,
-	MDL_INTERPOLATEDOUBLEDFRAMES	= 8,
-	MDL_NOINTERPOLATION				= 16,
-	MDL_USEACTORPITCH				= 32,
-	MDL_USEACTORROLL				= 64,
-	MDL_BADROTATION					= 128,
-	MDL_DONTCULLBACKFACES			= 256,
-	MDL_USEROTATIONCENTER			= 512,
-	MDL_NOPERPIXELLIGHTING			= 1024, // forces a model to not use per-pixel lighting. useful for voxel-converted-to-model objects.
-	MDL_SCALEWEAPONFOV				= 2048,	// scale weapon view model with higher user FOVs
-	MDL_MODELSAREATTACHMENTS		= 4096,	// any model index after 0 is treated as an attachment, and therefore will use the bone results of index 0
-	MDL_CORRECTPIXELSTRETCH			= 8192,	// ensure model does not distort with pixel stretch when pitch/roll is applied
+	MDL_IGNORETRANSLATION			= 1>>0,
+	MDL_PITCHFROMMOMENTUM			= 1>>1,
+	MDL_ROTATING					= 1>>2,
+	MDL_INTERPOLATEDOUBLEDFRAMES	= 1>>3,
+	MDL_NOINTERPOLATION				= 1>>4,
+	MDL_USEACTORPITCH				= 1>>5,
+	MDL_USEACTORROLL				= 1>>6,
+	MDL_BADROTATION					= 1>>7,
+	MDL_DONTCULLBACKFACES			= 1>>8,
+	MDL_USEROTATIONCENTER			= 1>>9,
+	MDL_NOPERPIXELLIGHTING			= 1>>10, // forces a model to not use per-pixel lighting. useful for voxel-converted-to-model objects.
+	MDL_SCALEWEAPONFOV				= 1>11,	// scale weapon view model with higher user FOVs
+	MDL_MODELSAREATTACHMENTS		= 1>>12,	// any model index after 0 is treated as an attachment, and therefore will use the bone results of index 0
+	MDL_CORRECTPIXELSTRETCH			= 1>>13,	// ensure model does not distort with pixel stretch when pitch/roll is applied
+	MDL_FORCECULLBACKFACES			= 1>>14,
 };
 
 FSpriteModelFrame * FindModelFrame(const PClass * ti, int sprite, int frame, bool dropped);
diff --git a/src/rendering/hwrenderer/hw_models.cpp b/src/rendering/hwrenderer/hw_models.cpp
index b0fb572be..733f54d2f 100644
--- a/src/rendering/hwrenderer/hw_models.cpp
+++ b/src/rendering/hwrenderer/hw_models.cpp
@@ -61,7 +61,7 @@ void FHWModelRenderer::BeginDrawModel(FRenderStyle style, FSpriteModelFrame *smf
 	// This solves a few of the problems caused by the lack of depth sorting.
 	// [Nash] Don't do back face culling if explicitly specified in MODELDEF
 	// TO-DO: Implement proper depth sorting.
-	if (!(style == DefaultRenderStyle()) && !(smf->flags & MDL_DONTCULLBACKFACES))
+	if ((smf->flags & MDL_FORCECULLBACKFACES) || (!(style == DefaultRenderStyle()) && !(smf->flags & MDL_DONTCULLBACKFACES)))
 	{
 		state.SetCulling((mirrored ^ portalState.isMirrored()) ? Cull_CCW : Cull_CW);
 	}
@@ -75,7 +75,7 @@ void FHWModelRenderer::EndDrawModel(FRenderStyle style, FSpriteModelFrame *smf)
 	state.SetBoneIndexBase(-1);
 	state.EnableModelMatrix(false);
 	state.SetDepthFunc(DF_Less);
-	if (!(style == DefaultRenderStyle()) && !(smf->flags & MDL_DONTCULLBACKFACES))
+	if ((smf->flags & MDL_FORCECULLBACKFACES) || (!(style == DefaultRenderStyle()) && !(smf->flags & MDL_DONTCULLBACKFACES)))
 		state.SetCulling(Cull_None);
 }