From: Mikko Rasa <tdb@tdb.fi>
Date: Fri, 11 Mar 2022 21:48:17 +0000 (+0200)
Subject: Flip normal if a surface faces away from the camera
X-Git-Url: http://git.tdb.fi/?a=commitdiff_plain;h=88c401224220010cb71426fafc5173661c4d48a3;p=libs%2Fgl.git

Flip normal if a surface faces away from the camera

This gives correct two-sided lighting for non-closed meshes, which may
be used for tree leaves and such.
---

diff --git a/shaderlib/common.glsl b/shaderlib/common.glsl
index 7a57b067..557d4d76 100644
--- a/shaderlib/common.glsl
+++ b/shaderlib/common.glsl
@@ -78,10 +78,12 @@ layout(location=0) out vec4 frag_color;
 
 virtual vec3 get_fragment_normal()
 {
+	vec3 normal;
+	float sgn = (gl_FrontFacing ? 1.0 : -1.0);
 	if(use_normal_map)
-		return normalize(world_tbn_matrix*(texture(normal_map, texcoord.xy).xyz*2.0-1.0));
+		return sgn*normalize(world_tbn_matrix*(texture(normal_map, texcoord.xy).xyz*2.0-1.0));
 	else
-		return normalize(world_normal);
+		return sgn*normalize(world_normal);
 }
 
 virtual IncomingLight get_incoming_light(int index, vec3 world_pos)