Hazel Game Engine (071) Frame Buffer

If there are errors in the code, terminology, etc. in the text, please correct me

foreword

• Introduction to framebuffer (my understanding)
  1. The scene rendered by OpenGL can be placed in this frame buffer
  2. This framebuffer can then be treated as a color or texture sampling area (depending on the type of buffer attachment attached to the framebuffer )
  3. Elsewhere (Imgui) render this frame buffer as a color texture, and the scene that should be displayed on the screen is displayed on the ImGui interface
• Framebuffer Reference URL
  • Blog of CSDN frame buffer
  • LearnOpenGL framebuffer

Framebuffer Essentials

• Need to manually create a frame buffer, just like creating a vertex buffer

• Additional information is required when creating a framebuffer

  Whether to store color textures, stencils, or depth buffers

  Additional buffers require additional buffer IDs

• Must be unbound every frame after binding

code flow

• Create a framebuffer and attach textures, depth and stencilbuffer textures

  void OpenGLFramebuffer::Invalidate()
  {
        
        
      // 1.创建帧缓冲
      glCreateFramebuffers(1, &m_RendererID);
      glBindFramebuffer(GL_FRAMEBUFFER, m_RendererID); // 绑定这个帧缓冲
  
      // 2.创建纹理
      glCreateTextures(GL_TEXTURE_2D, 1, &m_ColorAttachment);;
      glBindTexture(GL_TEXTURE_2D, m_ColorAttachment);
      // 旧的api吧
      glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, m_Specification.Width, m_Specification.Height, 0, GL_RGBA, GL_UNSIGNED_BYTE, nullptr);
      // 这里写错过，将glTexParameteri 写错成glTextureParameteri！！
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
      glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
  
      // 1.1纹理附加到帧缓冲
      glFramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, m_ColorAttachment, 0);
  
      // 3.创建深度模板缓冲纹理附加到帧缓冲中
      glCreateTextures(GL_TEXTURE_2D, 1, &m_DepthAttachment);;
      glBindTexture(GL_TEXTURE_2D, m_DepthAttachment);
      // 新api吧
      glTexStorage2D(GL_TEXTURE_2D, 1, GL_DEPTH24_STENCIL8, m_Specification.Width, m_Specification.Height);
      //glTexImage2D(GL_TEXTURE_2D, 0, GL_DEPTH24_STENCIL8, m_Specification.Width, m_Specification.Height, 0, GL_DEPTH_STENCIL, GL_UNSIGNED_INT_24_8, NULL);
  
      // 1.2深度模板缓冲纹理附加到帧缓冲中
      glFramebufferTexture2D(GL_FRAMEBUFFER, GL_DEPTH_STENCIL_ATTACHMENT, GL_TEXTURE_2D, m_DepthAttachment, 0);
  
      HZ_CORE_ASSERT(glCheckFramebufferStatus(GL_FRAMEBUFFER) == GL_FRAMEBUFFER_COMPLETE, "帧缓冲未创建完成");
  
      glBindFramebuffer(GL_FRAMEBUFFER, 0);// 取消绑定这个帧缓冲,以免不小心渲染到错误的帧缓冲上，比如深度、模板缓冲不会渲染到这里
  }
  

• Write data to the created framebuffer

  1. Bind a custom framebuffer (equivalent to unbinding to render to the default framebuffer)
  2. Render graphics normally (write the image originally rendered on the screen by OpenGL to a custom framebuffer (no longer the default framebuffer ))
  3. unbind framebuffer

  void Sandbox2D::OnUpdate(Hazel::Timestep ts)
  {
        
        
      HZ_PROFILE_FUNCTION();
  
      m_CameraController.OnUpdate(ts);
  
      // 渲染信息初始化
      Hazel::Renderer2D::ResetStats();
      {
        
        
          ///
          ///
          // 这里
          HZ_PROFILE_SCOPE("Renderer Prep");
          // 1.绑定自定义的帧缓冲（等于解绑到渲染到默认的帧缓冲中）
          m_Framebuffer->Bind();
          // 2.正常渲染图形（将本由OpenGL渲染在屏幕上的图像写入到自定义的帧缓冲中（不再是**默认的帧缓冲**中））
          Hazel::RenderCommand::SetClearColor({
        
         0.1f, 0.1f, 0.1f, 1 });
          Hazel::RenderCommand::Clear();
  		......
          Hazel::Renderer2D::DrawrRotatedQuad({
        
         1.0f, 0.5f }, {
        
         0.8f, 0.8f },30.0f, m_FlatColor);
          Hazel::Renderer2D::DrawQuad({
        
         -1.0f, 0.0f }, {
        
         0.8f, 0.8f }, m_FlatColor);
         .......
          // 3.解绑帧缓冲
          m_Framebuffer->Unbind();
      }
      ......
  

• Imgui renders a custom framebuffer

  ImGui::Begin("Settings");
  auto stats = Hazel::Renderer2D::GetStats();
  ImGui::Text("Renderer2D Stats:");
  ImGui::Text("Draw Calls: %d", stats.DrawCalls);
  ImGui::Text("Quads: %d", stats.QuadCount);
  ImGui::Text("Vertices: %d", stats.GetTotalVertexCount());
  ImGui::Text("Indices: %d", stats.GetTotalIndexCount());
  
  ImGui::ColorEdit4("Square Color", glm::value_ptr(m_FlatColor));
  // 这里/
  // imgui渲染帧缓冲中的东西(附在帧缓冲上的颜色纹理缓冲)
  uint32_t textureID = m_Framebuffer->GetColorAttachmentRendererID();
  ImGui::Image((void*)textureID, ImVec2{
        
         1280, 720 });
  
  ImGui::End();
  

• Effect

  

test framebuffer

• Do not unbind the framebuffer every frame

  The rendered framebuffer is a gray image

  

• Create framebuffer without attaching depth, stencilbuffer textures

  Depth detection failed , the one drawn later overrides the one drawn earlier