From e326a983893117508a6e94511c2f93913cd02256 Mon Sep 17 00:00:00 2001
From: David Thompson <dthompson2@worcester.edu>
Date: Fri, 6 Aug 2021 08:36:25 -0400
Subject: graphics: phong: Improve lighting.

---
 chickadee/graphics/phong.scm |  2 +-
 data/shaders/phong-frag.glsl | 31 +++++++++++++++++++++----------
 data/shaders/phong-vert.glsl |  2 +-
 3 files changed, 23 insertions(+), 12 deletions(-)

diff --git a/chickadee/graphics/phong.scm b/chickadee/graphics/phong.scm
index f52f10b..5288075 100644
--- a/chickadee/graphics/phong.scm
+++ b/chickadee/graphics/phong.scm
@@ -107,6 +107,6 @@
                     #:view view-matrix
                     #:projection (current-projection)
                     #:material material
-                    ;; #:camera-position camera-position
+                    #:camera-position camera-position
                     #:ambient-light-color ambient-light-color
                     #:lights lights))))
diff --git a/data/shaders/phong-frag.glsl b/data/shaders/phong-frag.glsl
index 84e9feb..9d8e40c 100644
--- a/data/shaders/phong-frag.glsl
+++ b/data/shaders/phong-frag.glsl
@@ -105,7 +105,7 @@ vec3 lightRadiance(Light light, vec3 direction) {
 
 vec3 materialAmbient() {
   if(material.useAmbientMap) {
-    return texture(material.ambientMap, fragTex).rgb * material.ambient;
+    return texture(material.ambientMap, fragTex).rgb;
   } else {
     return material.ambient;
   }
@@ -118,7 +118,7 @@ vec3 materialDiffuse() {
     if(color.a == 0.0) {
       discard;
     }
-    return color.rgb * material.diffuse;
+    return color.rgb;
   } else {
     return material.diffuse;
   }
@@ -126,7 +126,7 @@ vec3 materialDiffuse() {
 
 vec3 materialSpecular() {
   if(material.useSpecularMap) {
-    return texture(material.specularMap, fragTex).rgb * material.specular;
+    return texture(material.specularMap, fragTex).rgb;
   } else {
     return material.specular;
   }
@@ -134,13 +134,27 @@ vec3 materialSpecular() {
 
 vec3 materialNormal() {
   if(material.useBumpMap) {
-    return normalize(texture(material.bumpMap, fragTex).xyz * 2.0 - 1.0);
+    // Compute tangent space using fragment data rather than relying
+    // on tangent attributes.  See:
+    // http://www.thetenthplanet.de/archives/1180
+    vec3 tangentNormal = normalize(texture(material.bumpMap, fragTex).xyz * 2.0 - 1.0);
+    vec3 q1 = dFdx(fragWorldPos);
+    vec3 q2 = dFdy(fragWorldPos);
+    vec2 st1 = dFdx(fragTex);
+    vec2 st2 = dFdy(fragTex);
+    vec3 N = normalize(fragNorm);
+    vec3 T = normalize(q1 * st2.t - q2 * st1.t);
+    vec3 B = -normalize(cross(N, T));
+    mat3 TBN = mat3(T, B, N);
+
+    return normalize(TBN * tangentNormal);
   } else {
-    return fragNorm;
+    return normalize(fragNorm);
   }
 }
 
 void main() {
+  vec3 viewDir = normalize(cameraPosition - fragWorldPos);
   vec3 ambientOcclusion = materialAmbient();
   vec3 baseDiffuseColor = materialDiffuse();
   vec3 baseSpecularColor = materialSpecular();
@@ -160,16 +174,13 @@ void main() {
     float diffuseFactor = posDot(lightDir, normal);
     vec3 reflectDir = reflect(-lightDir, normal);
     vec3 diffuseColor = baseDiffuseColor * diffuseFactor;
-    float specularFactor = 0;
-    if(material.shininess > 0) {
-      specularFactor = pow(posDot(lightDir, reflectDir), material.shininess);
-    }
+    float specularFactor = pow(posDot(viewDir, reflectDir), material.shininess);
     vec3 specularColor = baseSpecularColor * specularFactor;
     color += (diffuseColor + specularColor) * radiance;
   }
 
   // Apply ambient lighting.
-  vec3 ambientColor = baseDiffuseColor * ambientOcclusion * ambientLightColor.rgb;
+  vec3 ambientColor = baseDiffuseColor * ambientLightColor.rgb * ambientOcclusion;
   color += ambientColor;
 
   // Apply gamma correction and HDR tone mapping to get the final
diff --git a/data/shaders/phong-vert.glsl b/data/shaders/phong-vert.glsl
index 9b72eb3..f7fd363 100644
--- a/data/shaders/phong-vert.glsl
+++ b/data/shaders/phong-vert.glsl
@@ -30,7 +30,7 @@ uniform mat4 projection;
 
 void main() {
   fragWorldPos = vec3(model * vec4(position, 1.0));
-  fragNorm = normalize(model * vec4(normal, 1.0)).xyz;
+  fragNorm = mat3(model) * normal;
   fragTex = texcoord;
   gl_Position = projection * view * vec4(fragWorldPos, 1.0);
 }
-- 
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