it works better that way, but there are lots of horrendous artifacts

shaders/lighting.frag.glsl

@@ -61,6 +61,11 @@ const float MAX_REFLECTION_LOD = 4.0;
 // FUNCTIONS
 
 #ifdef AMBIENT_LIGHT
+vec3 fresnelSchlickRoughness(float cosTheta, vec3 F0, float roughness)
+{
+    return F0 + (max(vec3(1.0 - roughness), F0) - F0) * pow(1.0 - cosTheta, 5.0);
+}
+
 vec3 GGX(
         in vec3 albedoColor,
         in float metallic,
@@ -71,20 +76,26 @@ vec3 GGX(
     float NdotV = max(dot(N, V), 0.0);
     vec3 R = reflect(-V, N);
     vec3 albedo = pow(albedoColor, vec3(2.2));
-    vec3 F0 = mix(vec3(0.04), albedo, metallic);
+    // calculate reflectance at normal incidence; if dia-electric (like plastic) use F0
+    // of 0.04 and if it's a metal, use their albedo color as F0 (metallic workflow)
+    vec3 F0 = vec3(0.04);
+    F0 = mix(F0, albedo, metallic);
 
     // ambient lighting (we now use IBL as the ambient term) (fresnelSchlickRoughness function)
-    vec3 F = F0 + (max(vec3(1.0 - roughness), F0) - F0) * pow(1.0 - NdotV, 5.0);
+    vec3 F = fresnelSchlickRoughness(NdotV, F0, roughness);
 
-    vec3 kD = 1.0 - F;
+    vec3 kS = F;
+    vec3 kD = 1.0 - kS;
     kD *= 1.0 - metallic;
 
-    vec3 irradiance = texture(ambientMap, inverseViewMatrix * N).rgb;
-    vec3 diffuse = irradiance * albedo;
+    mat3 viewToWorld = inverseViewMatrix;
+
+    vec3 irradiance = texture(ambientMap, viewToWorld*N).rgb;
+    vec3 diffuse      = irradiance * albedo;
 
     // sample both the pre-filter map and the BRDF lut and combine them together as per the Split-Sum approximation to get the IBL specular part.
 
-    vec3 prefilteredColor = textureLod(reflectMap, inverseViewMatrix * R, roughness * MAX_REFLECTION_LOD).rgb;
+    vec3 prefilteredColor = textureLod(reflectMap, viewToWorld * R, roughness * MAX_REFLECTION_LOD).rgb;
     vec2 brdf2 = texture(brdfLUT, vec2(NdotV, roughness)).rg;
     vec3 specular = prefilteredColor * (F * brdf2.x + brdf2.y);
 

shaders/skybox.frag.glsl

@@ -0,0 +1,25 @@
+#version 330 core
+
+// - Position in view space
+layout (location = 0) out vec4 outPosition;
+// - Albedo + Roughness
+layout (location = 1) out vec4 outAlbedo;
+// - Normal buffer
+layout (location = 2) out vec3 outNormal;
+// - Emission + Metallic
+layout (location = 3) out vec4 outEmission;
+
+in vec3 varTexCoord;
+
+out vec4 outColor;
+
+uniform samplerCube skybox;
+
+void main()
+{
+    outAlbedo.rgb = vec3(0., 0., 0.); // black
+    outAlbedo.a = 1.; // full roughness
+    outEmission.a = 0.; // not metallic
+    outNormal = vec3(0., 0., 1.); // oriented towards the eye
+    outEmission.rgb = texture(skybox, varTexCoord).rgb;
+}

shaders/skybox.vert.glsl

@@ -0,0 +1,13 @@
+#version 330 core
+
+layout(location = 0)in vec3 inPosition;
+
+out vec3 varTexCoord;
+
+uniform mat4 MVP;
+
+void main()
+{
+    gl_Position = MVP * vec4(inPosition, 1.0);
+    varTexCoord = inPosition;
+}

src/deferredpipeline.cpp

@@ -121,6 +121,12 @@ void DeferredPipeline::renderGL(Scene *scene)
     glClearColor(0.0f, 0.0f, 0.0f, 1.f);
     glClearDepth(1.0f);
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
+    // draw skybox
+    if(m_skybox != nullptr)
+    {
+        m_skybox->renderGL(m_camera);
+        glClear(GL_DEPTH_BUFFER_BIT);
+    }
     // loop on geometry
     for(SceneIterator<GeometryNode*>* geometryIt = scene->getGeometry();
         geometryIt->isValid(); geometryIt->next())
@@ -156,9 +162,6 @@ void DeferredPipeline::renderGL(Scene *scene)
     glEnable(GL_BLEND);
     glBlendFunc(GL_ONE, GL_ONE);
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
-    if(m_skybox != nullptr)
-        m_skybox->renderGL(m_camera);
-
     m_gBuffer->bindTextures();
     for(SceneIterator<Light*>* lightIt = scene->getLights();
         lightIt->isValid(); lightIt->next())

src/skybox.cpp

@@ -6,9 +6,12 @@
 #include "texture.h"
 #include "camera.h"
 #include "opengl.h"
+#include <resource.h>
 
 #define BUFFER_OFFSET(i) ((char *)NULL + (i))
 
+RESOURCE_PACK(shaders)
+
 Skybox::Skybox(Texture* myCubeMap)
 {
     cubeMap = myCubeMap;
@@ -24,6 +27,10 @@ Skybox::Skybox(Texture* myCubeMap)
     glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3*sizeof(GLfloat), BUFFER_OFFSET(0));
     glEnableVertexAttribArray(0);
 	
+    Resource::ResourceMap shaderMap;
+    Resource::getResourcePack_shaders(shaderMap);
+    std::string vertSource = shaderMap["shaders/skybox.vert.glsl"];
+    std::string fragSource = shaderMap["shaders/skybox.frag.glsl"];
     shader = new Shader(vertSource, fragSource);
     mvpLocation = shader->getLocation("MVP");
     cubemapLocation = shader->getLocation("skybox");
@@ -39,10 +46,7 @@ Skybox::~Skybox()
 
 void Skybox::renderGL(Camera* myCamera)
 {
-    glViewport(0, 0, width, height);
     glm::mat4 viewMatrix = glm::mat4(glm::mat3(myCamera->getViewMatrix()));
-    glDisable(GL_CULL_FACE);
-    glDepthMask(GL_FALSE);
 	
     shader->bind();
     shader->bindMat4(mvpLocation, myCamera->getProjectionMatrix() * viewMatrix);
@@ -53,9 +57,6 @@ void Skybox::renderGL(Camera* myCamera)
     glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, vbos[0]);
     glDrawElements(GL_TRIANGLES, 36, GL_UNSIGNED_BYTE, NULL);
     glBindVertexArray(0);
-
-    glEnable(GL_CULL_FACE);
-    glDepthMask(GL_TRUE);
 }
 
 const GLfloat Skybox::skyboxVertices[] = {
@@ -83,24 +84,3 @@ const GLubyte Skybox::skyboxIndices[] = {
     2, 6, 3,
     6, 7, 3
 };
-
-const std::string Skybox::vertSource =
-        "#version 330 core\n\
-        layout(location = 0)in vec3 inPosition;\n\
-        out vec3 varTexCoord;\n\
-        uniform mat4 MVP;\n\
-        void main()\n\
-        {\n\
-            gl_Position = MVP * vec4(inPosition, 1.0);\n\
-            varTexCoord = inPosition;\n\
-        }\n";
-
-const std::string Skybox::fragSource =
-        "#version 330 core\n\
-        in vec3 varTexCoord;\n\
-        out vec4 outColor;\n\
-        uniform samplerCube skybox;\n\
-        void main()\n\
-        {\n\
-            outColor = texture(skybox, varTexCoord);\n\
-        }\n";

src/skybox.h

@@ -12,8 +12,6 @@ class Skybox
 {
     static const GLfloat skyboxVertices[];
     static const GLubyte skyboxIndices[];
-    static const std::string vertSource;
-    static const std::string fragSource;
 
     int width;
     int height;