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+;;; Chickadee Game Toolkit
+;;; Copyright © 2019 David Thompson <davet@gnu.org>
+;;;
+;;; Chickadee is free software: you can redistribute it and/or modify
+;;; it under the terms of the GNU General Public License as published
+;;; by the Free Software Foundation, either version 3 of the License,
+;;; or (at your option) any later version.
+;;;
+;;; Chickadee is distributed in the hope that it will be useful, but
+;;; WITHOUT ANY WARRANTY; without even the implied warranty of
+;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+;;; General Public License for more details.
+;;;
+;;; You should have received a copy of the GNU General Public License
+;;; along with this program.  If not, see
+;;; <http://www.gnu.org/licenses/>.
+
+;;; Commentary:
+;;
+;; Simple forward rendered Phong lighting model.
+;;
+;;; Code:
+
+(define-module (chickadee render phong)
+  #:use-module (chickadee math vector)
+  #:use-module (chickadee render)
+  #:use-module (chickadee render color)
+  #:use-module (chickadee render shader)
+  #:use-module (srfi srfi-9)
+  #:export (make-phong-material
+            phong-material?
+            phong-material-name
+            phong-material-ambient
+            phong-material-diffuse
+            phong-material-specular
+            phong-material-specular-exponent
+            default-phong-material
+            load-phong-shader
+            gpu-apply/phong))
+
+
+;;;
+;;; Phong Material
+;;;
+
+(define-shader-type <phong-material>
+  make-phong-material
+  phong-material?
+  (local-field name phong-material-name)
+  (float-vec3 ambient phong-material-ambient)
+  (float-vec3 diffuse phong-material-diffuse)
+  (float-vec3 specular phong-material-specular)
+  (float shininess phong-material-shininess))
+
+(define default-phong-material
+  (make-phong-material #:name "default"
+                       #:ambient (vec3 0.5 0.5 0.5)
+                       #:diffuse (vec3 0.5 0.5 0.5)
+                       #:specular (vec3 0.5 0.5 0.5)
+                       #:shininess 32.0))
+
+
+;;;
+;;; Lights
+;;;
+
+(define-shader-type <directional-light>
+  make-directional-light
+  directional-light?
+  (float-vec4 color directional-light-color)
+  (float-vec3 direction directional-light-direction)
+  (float-vec3 ambient directional-light-ambient)
+  (float-vec3 diffuse directional-light-diffuse)
+  (float-vec3 specular directional-light-specular)
+  (float shininess directional-light-shininess))
+
+(define default-directional-light
+  (make-directional-light #:color white
+                          #:direction (vec3 -1.0 0.0 -1.0)
+                          #:ambient (vec3 0.5 0.5 0.5)
+                          #:diffuse (vec3 0.5 0.5 0.5)
+                          #:specular (vec3 0.5 0.5 0.5)
+                          #:shininess 32.0))
+
+
+;;;
+;;; Phong Shader
+;;;
+
+(define phong-shader
+  (delay
+    (strings->shader
+     "
+#version 130
+
+in vec3 position;
+in vec2 texcoord;
+in vec3 normal;
+
+uniform mat4 model;
+uniform mat4 view;
+uniform mat4 projection;
+
+out vec3 fragNorm;
+out vec2 fragTex;
+
+void main() {
+    gl_Position = projection * view * model * vec4(position, 1.0);
+    // TODO: Calculate normal matrix on CPU
+    fragNorm = normalize(model * vec4(normal, 1.0)).xyz;
+    fragTex = texcoord;
+}
+"
+     "
+#version 130
+
+struct Material {
+  vec3 ambient;
+  vec3 diffuse;
+  vec3 specular;
+  float shininess;
+};
+
+struct DirectionalLight {
+    vec4 color;
+    vec3 direction;
+    vec3 ambient;
+    vec3 diffuse;
+    vec3 specular;
+};
+
+in vec3 fragNorm;
+in vec2 fragTex;
+
+uniform Material material;
+uniform DirectionalLight directionalLight;
+
+void main() {
+    vec3 lightColor = directionalLight.color.xyz;
+    vec3 ambientColor = material.ambient * lightColor;
+    vec3 lightDir = normalize(-directionalLight.direction);
+    float diffuseFactor = max(dot(lightDir, fragNorm), 0.0);
+    vec3 diffuseColor = diffuseFactor * material.diffuse * lightColor;
+    vec3 reflectDir = reflect(-lightDir, fragNorm);
+    float specularFactor = pow(max(dot(lightDir, reflectDir), 0.0), material.shininess);
+    vec3 specularColor = specularFactor * material.specular * lightColor;
+    gl_FragColor = vec4(ambientColor + diffuseColor + specularColor, 1.0);
+}
+")))
+
+(define (load-phong-shader)
+  (force phong-shader))
+
+(define (gpu-apply/phong shader vertex-array material model-matrix view-matrix)
+  (gpu-apply shader vertex-array
+             #:model model-matrix
+             #:view view-matrix
+             #:projection (current-projection)
+             #:material material
+             #:directional-light default-directional-light))