From 7a4f04f1df6896a4978ba302ea3fc79b6e7dd1f7 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Mon, 16 Aug 2021 17:12:23 -0400
Subject: graphics: Add basic image based ambient lighting.

---
 data/shaders/pbr-frag.glsl   | 14 +++++++++-----
 data/shaders/phong-frag.glsl | 11 ++++++++---
 2 files changed, 17 insertions(+), 8 deletions(-)

(limited to 'data')

diff --git a/data/shaders/pbr-frag.glsl b/data/shaders/pbr-frag.glsl
index c474981..fff725a 100644
--- a/data/shaders/pbr-frag.glsl
+++ b/data/shaders/pbr-frag.glsl
@@ -47,9 +47,9 @@ out vec4 fragColor;
 
 uniform Material material;
 uniform Light lights[MAX_LIGHTS];
-uniform vec4 ambientLight;
 uniform bool vertexColored;
 uniform vec3 cameraPosition;
+uniform samplerCube skybox;
 uniform sampler2D baseColorTexture;
 uniform sampler2D metallicRoughnessTexture;
 uniform sampler2D normalTexture;
@@ -244,6 +244,7 @@ void main(void) {
   float metallic = materialMetallic();
   float roughness = materialRoughness();
   vec3 normal = materialNormal();
+  vec3 reflection = reflect(-viewDirection, normal);
   // The "raw" albedo has an alpha channel which we need to preserve
   // so that we can apply the desired alpha blending method at the
   // end, but it is completely ignored for lighting calculations.
@@ -356,11 +357,14 @@ void main(void) {
   // The emissive texture says which fragments emit light.  We simply
   // add this light value to the color accumulator.
   color += materialEmissive();
-  // Apply simple ambient lighting.  The affect of the ambient light
-  // is dampened by the ambient occlusion factor.
+  // Apply image based ambient lighting.  The affect of the ambient
+  // light is dampened by the ambient occlusion factor.
   //
-  // TODO: Use image based lighting.
-  color += ambientLight.rgb * albedo * ambientOcclusion;
+  // TODO: Use fancy PBR equations instead of these basic ones.
+  float fresnel = pow(1.0 - clamp(dot(viewDirection, normal), 0.0, 1.0), 5);
+  vec3 ambientDiffuse = textureCube(skybox, normal).rgb;
+  vec3 ambientSpecular = textureLod(skybox, reflection, roughness * 7.0).rgb;
+  color += (ambientDiffuse * albedo + ambientSpecular * fresnel) * ambientOcclusion;
   // Apply Reinhard tone mapping to convert our high dynamic range
   // color value to low dynamic range.  All of the lighting
   // calculations stacked on top of each other is likely to create
diff --git a/data/shaders/phong-frag.glsl b/data/shaders/phong-frag.glsl
index 0beb75b..9c86c83 100644
--- a/data/shaders/phong-frag.glsl
+++ b/data/shaders/phong-frag.glsl
@@ -32,6 +32,7 @@ in vec2 fragTex;
 out vec4 fragColor;
 #endif
 
+uniform samplerCube skybox;
 uniform sampler2D ambientMap;
 uniform sampler2D diffuseMap;
 uniform sampler2D specularMap;
@@ -39,7 +40,6 @@ uniform sampler2D normalMap;
 uniform Material material;
 uniform Light lights[MAX_LIGHTS];
 uniform vec3 cameraPosition;
-uniform vec4 ambientLight;
 
 const float GAMMA = 2.2;
 
@@ -135,6 +135,7 @@ void main() {
   vec3 diffuseColor = materialDiffuse();
   vec3 specularColor = materialSpecular();
   vec3 normal = materialNormal();
+  vec3 reflection = reflect(-viewDir, normal);
   vec3 color = vec3(0.0);
 
   // Apply direct lighting.
@@ -155,8 +156,12 @@ void main() {
     color += diffuseLight * diffuseColor + specularLight * specularColor;
   }
 
-  // Apply ambient lighting.
-  vec3 ambientColor = diffuseColor * ambientLight.rgb * ambientOcclusion;
+  // Apply image based ambient lighting.
+  float fresnel = pow(1.0 - clamp(dot(viewDir, normal), 0.0, 1.0), 5);
+  float roughness = 1.0 - (material.shininess / 1000.0);
+  vec3 ambientDiffuse = textureCube(skybox, normal).rgb * diffuseColor;
+  vec3 ambientSpecular = textureLod(skybox, reflection, roughness * 7.0).rgb * fresnel;
+  vec3 ambientColor = (ambientDiffuse + ambientSpecular) * ambientOcclusion;
   color += ambientColor;
 
   // Apply gamma correction and HDR tone mapping to get the final
-- 
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