Implement Multi-Sample Anti Aliasing (MSAA)

src/main.cc

@@ -50,8 +50,13 @@
 
 #define WIREFRAME 0
 #define NORMALS 0
+#define MSAA 1
 #define POINT_LIGHTS 1
 
+#if MSAA
+#define MSAA_SAMPLE_COUNT 4
+#endif
+
 enum exit_codes : int {
   EXIT_CODE_SUCCESS,
   EXIT_CODE_SDL_INIT_FAILED,
@@ -149,9 +154,15 @@ struct FrameBuffer {
   GLuint fbo;
   GLuint color;
   GLuint depth_stencil;
+  GLuint width;
+  GLuint height;
 };
 
-FrameBuffer create_frame_buffer(unsigned int width, unsigned int height);
+FrameBuffer create_normal_frame_buffer(unsigned int width, unsigned int height);
+#if MSAA
+FrameBuffer create_multisample_frame_buffer(unsigned int width, unsigned int height);
+void blit_multisample_frame_buffer(const FrameBuffer &multisample_buffer, const FrameBuffer &normal_buffer);
+#endif
 void delete_frame_buffer(FrameBuffer &buffer);
 GLuint load_cubemap(std::vector<std::string> textures);
 
@@ -166,6 +177,11 @@ int main() {
   SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 3);
   SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
 
+#if MSAA
+  SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS, 1);
+  SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES, MSAA_SAMPLE_COUNT);
+#endif
+
   SDL_Window *window = SDL_CreateWindow("Window", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED,
                                         WINDOW_WIDTH, WINDOW_HEIGHT, SDL_WINDOW_OPENGL | SDL_WINDOW_RESIZABLE);
   if (!window) {
@@ -181,12 +197,21 @@ int main() {
     return EXIT_CODE_GLAD_LOADER_FAILED;
   }
 
+#if MSAA
+  glEnable(GL_MULTISAMPLE);
+#endif
+
   SDL_SetRelativeMouseMode(SDL_TRUE);
   SDL_WarpMouseInWindow(window, WINDOW_HALF_WIDTH, WINDOW_HALF_HEIGHT);
 
   glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
 
-  FrameBuffer offscreen_buffer = create_frame_buffer(WINDOW_WIDTH, WINDOW_HEIGHT);
+#if MSAA
+  FrameBuffer multisample_buffer = create_multisample_frame_buffer(WINDOW_WIDTH, WINDOW_HEIGHT);
+  FrameBuffer offscreen_buffer   = create_normal_frame_buffer(WINDOW_WIDTH, WINDOW_HEIGHT);
+#else
+  FrameBuffer offscreen_buffer = create_normal_frame_buffer(WINDOW_WIDTH, WINDOW_HEIGHT);
+#endif
 
   std::vector<Vertex> vertices = {
     // positions                           // normals                      // texture coords
@@ -497,7 +522,11 @@ int main() {
 
             // Recreate offscreen frame buffer
             delete_frame_buffer(offscreen_buffer);
-            offscreen_buffer = create_frame_buffer(w, h);
+            offscreen_buffer = create_normal_frame_buffer(w, h);
+#if MSAA
+            delete_frame_buffer(multisample_buffer);
+            multisample_buffer = create_multisample_frame_buffer(w, h);
+#endif
           }
           break;
       }
@@ -523,7 +552,11 @@ int main() {
     skybox_shader.set_mat4("sb_view", glm::mat4(glm::mat3(view)));
 
     // Main render pass
+#if MSAA
+    glBindFramebuffer(GL_FRAMEBUFFER, multisample_buffer.fbo);
+#else
     glBindFramebuffer(GL_FRAMEBUFFER, offscreen_buffer.fbo);
+#endif
 
     glClearColor(0.04f, 0.08f, 0.08f, 1.0f);
     glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
@@ -578,6 +611,10 @@ int main() {
     glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
 #endif
 
+#if MSAA
+    blit_multisample_frame_buffer(multisample_buffer, offscreen_buffer);
+#endif
+
     // Post processing pass
     glBindFramebuffer(GL_FRAMEBUFFER, 0);
 
@@ -959,7 +996,7 @@ std::vector<Texture2D> Model::load_material_textures(aiMaterial *material, aiTex
   return textures;
 }
 
-FrameBuffer create_frame_buffer(unsigned int width, unsigned int height) {
+FrameBuffer create_normal_frame_buffer(unsigned int width, unsigned int height) {
   FrameBuffer buffer = {};
 
   glGenFramebuffers(1, &buffer.fbo);
@@ -990,9 +1027,61 @@ FrameBuffer create_frame_buffer(unsigned int width, unsigned int height) {
   glBindTexture(GL_TEXTURE_2D, 0);
   glBindRenderbuffer(GL_RENDERBUFFER, 0);
 
+  buffer.width  = width;
+  buffer.height = height;
+
   return buffer;
 }
 
+#if MSAA
+FrameBuffer create_multisample_frame_buffer(unsigned int width, unsigned int height) {
+  FrameBuffer buffer = {};
+
+  glGenFramebuffers(1, &buffer.fbo);
+  glBindFramebuffer(GL_FRAMEBUFFER, buffer.fbo);
+
+  // Create color texture
+  glGenTextures(1, &buffer.color);
+  glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, buffer.color);
+  glTexImage2DMultisample(GL_TEXTURE_2D_MULTISAMPLE, MSAA_SAMPLE_COUNT, GL_RGB, width, height, GL_TRUE);
+  glTexParameteri(GL_TEXTURE_2D_MULTISAMPLE, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+  glTexParameteri(GL_TEXTURE_2D_MULTISAMPLE, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+
+  glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D_MULTISAMPLE, buffer.color, 0);
+
+  // Create depth and stencil buffers
+  glGenRenderbuffers(1, &buffer.depth_stencil);
+  glBindRenderbuffer(GL_RENDERBUFFER, buffer.depth_stencil);
+  glRenderbufferStorageMultisample(GL_RENDERBUFFER, MSAA_SAMPLE_COUNT, GL_DEPTH24_STENCIL8, width, height);
+
+  glFramebufferRenderbuffer(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_RENDERBUFFER, buffer.depth_stencil);
+
+  if (glCheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE) {
+    printf("Incomplete frame buffer\n");
+    exit(EXIT_CODE_INCOMPLETE_FRAME_BUFFER);
+  }
+
+  glBindFramebuffer(GL_FRAMEBUFFER, 0);
+  glBindTexture(GL_TEXTURE_2D_MULTISAMPLE, 0);
+  glBindRenderbuffer(GL_RENDERBUFFER, 0);
+
+  buffer.width  = width;
+  buffer.height = height;
+
+  return buffer;
+}
+
+void blit_multisample_frame_buffer(const FrameBuffer &multisample_buffer, const FrameBuffer &normal_buffer) {
+  glBindFramebuffer(GL_READ_FRAMEBUFFER, multisample_buffer.fbo);
+  glBindFramebuffer(GL_DRAW_FRAMEBUFFER, normal_buffer.fbo);
+  glBlitFramebuffer(
+      0, 0, multisample_buffer.width, multisample_buffer.height,
+      0, 0, normal_buffer.width, normal_buffer.height,
+      GL_COLOR_BUFFER_BIT, GL_NEAREST
+  );
+}
+#endif
+
 void delete_frame_buffer(FrameBuffer &buffer) {
   glDeleteFramebuffers(1, &buffer.fbo);
   glDeleteTextures(1, &buffer.color);