Use instanced arrays to draw the lights

shaders/light_vert.glsl

@@ -0,0 +1,18 @@
+#version 330 core
+
+#define POINT_LIGHT_COUNT 4
+
+layout(location=0) in vec3 position;
+layout(location=1) in vec3 normal;
+layout(location=2) in vec2 uv;
+layout(location=3) in mat4 model;
+
+layout (std140) uniform Common {
+  mat4 projection;
+  mat4 view;
+  vec3 camera_position;
+};
+
+void main() {
+  gl_Position = projection * view * model * vec4(position, 1.0);
+};

src/main.cc

@@ -50,7 +50,7 @@
 
 #define WIREFRAME 0
 #define NORMALS 0
-#define POINT_LIGHTS 0
+#define POINT_LIGHTS 1
 
 enum exit_codes : int {
   EXIT_CODE_SUCCESS,
@@ -116,10 +116,14 @@ class Mesh {
     std::vector<Texture2D> textures;
 
     Mesh(std::vector<Vertex> vertices, std::vector<GLuint> indices, std::vector<Texture2D> textures);
+    void activate();
+    void deactivate();
     void draw(Shader &Shader);
+    void draw_instanced(Shader &Shader, unsigned int count = 1);
   private:
     GLuint vao, vbo, ebo;
     void setup_mesh();
+    void set_mesh_textures_for_drawing(Shader &shader);
 };
 
 class Model {
@@ -282,7 +286,8 @@ int main() {
 #endif
 
 #if POINT_LIGHTS
-  Shader light_shader      {"shaders/vert.glsl",        "shaders/light_frag.glsl"};
+  Shader light_shader      {"shaders/light_vert.glsl",  "shaders/light_frag.glsl"};
+  std::vector<glm::mat4> light_shader_model_mats;
 #endif
 
   const float camera_speed  = 25.0f;
@@ -356,8 +361,36 @@ int main() {
     memset(constant,  0, sizeof(constant));
     memset(linear,    0, sizeof(linear));
     memset(quadratic, 0, sizeof(quadratic));
+
+#if POINT_LIGHTS
+    glm::mat4 light_shader_model_mat = glm::translate(glm::mat4(1.0f), point_light_positions[i]);
+    light_shader_model_mat = glm::scale(light_shader_model_mat, glm::vec3(0.2f));
+    light_shader_model_mats.push_back(light_shader_model_mat);
+#endif
   }
 
+#if POINT_LIGHTS
+  std::size_t vec4_size = sizeof(glm::vec4);
+
+  light.activate();
+
+  GLuint instanceVBO;
+  glGenBuffers(1, &instanceVBO);
+  glBindBuffer(GL_ARRAY_BUFFER, instanceVBO);
+  glBufferData(GL_ARRAY_BUFFER, sizeof(glm::mat4) * light_shader_model_mats.size(), glm::value_ptr(light_shader_model_mats[0]), GL_STATIC_DRAW);
+
+  // Set up attribute pointers for each column of the matrix
+  for (unsigned int i = 3; i < 7; ++i) {
+    glVertexAttribPointer(i, 4, GL_FLOAT, GL_FALSE, 4 * vec4_size, (void *)((i - 3) * vec4_size));
+    glEnableVertexAttribArray(i);
+    glVertexAttribDivisor(i, 1);
+  }
+
+  light.deactivate();
+
+  glBindBuffer(GL_ARRAY_BUFFER, 0);
+#endif
+
   // Load cube map
   std::vector<std::string> cube_map_textures = {
     "images/skybox/right.jpg",
@@ -526,22 +559,14 @@ int main() {
     refractive_shader.set_mat4("model", model);
     refractive_shader.set_mat3("normal_mat", normal_mat);
     suzanne.draw(refractive_shader);
-    glEnable(GL_CULL_FACE);
 
 #if POINT_LIGHTS
     // Draw point lights
-    for (int i = 0; i < point_light_positions.size(); ++i) {
-      model = glm::translate(glm::mat4(1.0f), point_light_positions[i]);
-      model = glm::scale(model, glm::vec3(0.2f));
-      light_shader.activate();
-      light_shader.set_mat4("model", model);
-      light_shader.set_vec3("light_diffuse", light_diffuse);
-      light.draw(light_shader);
-    }
+    light_shader.set_vec3("light_diffuse", light_diffuse);
+    light.draw_instanced(light_shader, point_light_positions.size());
 #endif
 
     // Draw skybox
-    glDisable(GL_CULL_FACE);
     skybox_shader.activate();
     glActiveTexture(GL_TEXTURE0);
     glBindTexture(GL_TEXTURE_CUBE_MAP, cubemap);
@@ -803,7 +828,7 @@ void Mesh::setup_mesh() {
   glEnableVertexAttribArray(2);
 }
 
-void Mesh::draw(Shader &shader) {
+void Mesh::set_mesh_textures_for_drawing(Shader &shader) {
   unsigned int diffuse = 1;
   unsigned int specular = 1;
   unsigned int index;
@@ -814,9 +839,27 @@ void Mesh::draw(Shader &shader) {
     shader.set_int(texture.name(index).c_str(), texture.texture_unit - GL_TEXTURE0);
     texture.activate();
   }
+}
 
+void Mesh::activate() {
   glBindVertexArray(vao);
+}
+
+void Mesh::deactivate() {
+  glBindVertexArray(0);
+}
+
+void Mesh::draw(Shader &shader) {
+  set_mesh_textures_for_drawing(shader);
+  activate();
   glDrawElements(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, (void *)0);
+  deactivate();
+}
+
+void Mesh::draw_instanced(Shader &shader, unsigned int count) {
+  set_mesh_textures_for_drawing(shader);
+  glBindVertexArray(vao);
+  glDrawElementsInstanced(GL_TRIANGLES, indices.size(), GL_UNSIGNED_INT, (void *)0, count);
   glBindVertexArray(0);
 }