From b6faadca0333ae3f2a16f41978fbae803026e267 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tomasz=20Kapu=C5=9Bci=C5=84ski?= <tomaszkax86@gmail.com>
Date: Thu, 11 Feb 2016 15:04:07 +0100
Subject: [PATCH] Rewritten OpenGL 2.1 engine's two-sided lighting

---
 src/graphics/opengl/gl21device.cpp            |  2 ++
 .../shaders/fragment_shader_21_pervertex.glsl | 21 +++++++++----
 .../shaders/vertex_shader_21_pervertex.glsl   | 30 +++++++++++++------
 3 files changed, 38 insertions(+), 15 deletions(-)

diff --git a/src/graphics/opengl/gl21device.cpp b/src/graphics/opengl/gl21device.cpp
index 8a4fcd90..7c1c9cbb 100644
--- a/src/graphics/opengl/gl21device.cpp
+++ b/src/graphics/opengl/gl21device.cpp
@@ -388,6 +388,8 @@ bool CGL21Device::Create()
     for (int i = 0; i < 8; i++)
         glUniform1i(uni_Light[i].Enabled, 0);
 
+    glEnable(GL_VERTEX_PROGRAM_TWO_SIDE);
+
     // create default framebuffer object
     FramebufferParams framebufferParams;
 
diff --git a/src/graphics/opengl/shaders/fragment_shader_21_pervertex.glsl b/src/graphics/opengl/shaders/fragment_shader_21_pervertex.glsl
index 7d965553..5e4ba055 100644
--- a/src/graphics/opengl/shaders/fragment_shader_21_pervertex.glsl
+++ b/src/graphics/opengl/shaders/fragment_shader_21_pervertex.glsl
@@ -35,27 +35,36 @@ uniform vec4 uni_FogColor;
 uniform float uni_ShadowColor;
 
 varying float pass_Distance;
+varying vec4 pass_Color;
+varying vec3 pass_Normal;
+varying vec2 pass_TexCoord0;
+varying vec2 pass_TexCoord1;
+varying vec3 pass_TexCoord2;
+
+const vec3 const_LightDirection = vec3(1.0f, 2.0f, -1.0f);
 
 void main()
 {
-    vec4 color = gl_Color;
+    vec4 color = pass_Color;
 
     if (uni_TextureEnabled[0])
     {
-        color = color * texture2D(uni_PrimaryTexture, gl_TexCoord[0].st);
+        color = color * texture2D(uni_PrimaryTexture, pass_TexCoord0);
     }
 
     if (uni_TextureEnabled[1])
     {
-        color = color * texture2D(uni_SecondaryTexture, gl_TexCoord[1].st);
+        color = color * texture2D(uni_SecondaryTexture, pass_TexCoord1);
     }
 
     if (uni_TextureEnabled[2])
     {
-        if (gl_FrontFacing)
-            color.rgb *= mix(uni_ShadowColor, 1.0f, shadow2D(uni_ShadowTexture, gl_TexCoord[2].xyz).x);
-        else
+        vec3 normal = pass_Normal * (2.0f * gl_Color.x - 1.0f);
+
+        if (dot(normal, const_LightDirection) < 0.0f)
             color.rgb *= uni_ShadowColor;
+        else
+            color.rgb *= mix(uni_ShadowColor, 1.0f, shadow2D(uni_ShadowTexture, pass_TexCoord2).x);
     }
 
     if (uni_FogEnabled)
diff --git a/src/graphics/opengl/shaders/vertex_shader_21_pervertex.glsl b/src/graphics/opengl/shaders/vertex_shader_21_pervertex.glsl
index e2b93157..b0bf8e67 100644
--- a/src/graphics/opengl/shaders/vertex_shader_21_pervertex.glsl
+++ b/src/graphics/opengl/shaders/vertex_shader_21_pervertex.glsl
@@ -44,18 +44,21 @@ uniform bool uni_LightingEnabled;
 uniform LightParams uni_Light[8];
 
 varying float pass_Distance;
+varying vec4 pass_Color;
+varying vec3 pass_Normal;
+varying vec2 pass_TexCoord0;
+varying vec2 pass_TexCoord1;
+varying vec3 pass_TexCoord2;
 
 void main()
 {
     vec4 position = uni_ModelMatrix * gl_Vertex;
     vec4 eyeSpace = uni_ViewMatrix * position;
     vec4 shadowCoord = uni_ShadowMatrix * position;
-    gl_Position = uni_ProjectionMatrix * eyeSpace;
-    gl_FrontColor = gl_Color;
-    gl_TexCoord[0] = gl_MultiTexCoord0;
-    gl_TexCoord[1] = gl_MultiTexCoord1;
-    gl_TexCoord[2] = vec4(shadowCoord.xyz / shadowCoord.w, 1.0f);
-    pass_Distance = abs(eyeSpace.z / eyeSpace.w);
+
+    vec4 color = gl_Color;
+
+    vec3 normal = normalize((uni_NormalMatrix * vec4(gl_Normal, 0.0f)).xyz);
 
     if (uni_LightingEnabled)
     {
@@ -63,8 +66,6 @@ void main()
         vec4 diffuse = vec4(0.0f);
         vec4 specular = vec4(0.0f);
 
-        vec3 normal = normalize((uni_NormalMatrix * vec4(gl_Normal, 0.0f)).xyz);
-
         for (int i = 0; i < 8; i++)
         {
             if (uni_Light[i].Enabled)
@@ -97,6 +98,17 @@ void main()
                 + uni_DiffuseColor * diffuse
                 + uni_SpecularColor * specular;
 
-        gl_FrontColor = vec4(min(vec3(1.0f), result.rgb), 1.0f);
+        color = vec4(min(vec3(1.0f), result.rgb), 1.0f);
     }
+
+    gl_Position = uni_ProjectionMatrix * eyeSpace;
+    gl_FrontColor = vec4(1.0f);
+    gl_BackColor = vec4(0.0f);
+
+    pass_Distance = abs(eyeSpace.z / eyeSpace.w);
+    pass_Color = color;
+    pass_Normal = normal;
+    pass_TexCoord0 = gl_MultiTexCoord0.st;
+    pass_TexCoord1 = gl_MultiTexCoord1.st;
+    pass_TexCoord2 = shadowCoord.xyz / shadowCoord.w;
 }