From 679518f8e57e436c01972cba927b2e8edb8a003f Mon Sep 17 00:00:00 2001
From: Rachael Alexanderson <madame-rachelle@users.noreply.github.com>
Date: Tue, 3 May 2022 23:39:40 -0400
Subject: [PATCH] - model normals fix

---
 wadsrc/static/shaders/glsl/main.fp | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/wadsrc/static/shaders/glsl/main.fp b/wadsrc/static/shaders/glsl/main.fp
index 15af579a9..a46a09bea 100644
--- a/wadsrc/static/shaders/glsl/main.fp
+++ b/wadsrc/static/shaders/glsl/main.fp
@@ -5,8 +5,8 @@ layout(location = 1) in vec4 vColor;
 layout(location = 2) in vec4 pixelpos;
 layout(location = 3) in vec3 glowdist;
 layout(location = 4) in vec3 gradientdist;
-layout(location = 5) in vec4 vWorldNormal;
-layout(location = 6) in vec4 vEyeNormal;
+layout(location = 5) in vec4 vWorldNormalOrig;
+layout(location = 6) in vec4 vEyeNormalOrig;
 layout(location = 9) in vec3 vLightmap;
 
 #ifdef NO_CLIPDISTANCE_SUPPORT
@@ -20,6 +20,9 @@ layout(location=1) out vec4 FragFog;
 layout(location=2) out vec4 FragNormal;
 #endif
 
+vec4 vWorldNormal;
+vec4 vEyeNormal;
+
 struct Material
 {
 	vec4 Base;
@@ -720,6 +723,15 @@ void main()
 	if (ClipDistanceA.x < 0 || ClipDistanceA.y < 0 || ClipDistanceA.z < 0 || ClipDistanceA.w < 0 || ClipDistanceB.x < 0) discard;
 #endif
 
+	// Flip normal if it is facing away from the camera
+	vWorldNormal = vWorldNormalOrig;
+	vEyeNormal = vEyeNormalOrig;
+	if (dot(uCameraPos.xyz - pixelpos.xyz, vWorldNormal.xyz) < 0)
+	{
+		vWorldNormal.xyz = -vWorldNormal.xyz;
+		vEyeNormal.xyz = -vEyeNormal.xyz;
+	}
+
 #ifndef LEGACY_USER_SHADER
 	Material material;