Hazel Game Engine (097) Fill additional buffer of framebuffer with fixed value

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

Preface

• Recap

  1. From the previous section, you can already read the value of the color buffer at the mouse position.
  2. But when reading the value which is not a range of quad it is a strange number
  3. It's because glClearColor(color.r, color.g, color.b, color.a); is used in the cpp code to fill the buffer with color by default .
  4. This color is originally a float value, but when converted to int, it is read as a strange number.

• of this program

  Reading a value from a range that is not a quad returns a specific **-1** value

• How to achieve

  Use the new OpenGL function glClearTexImage to fill a buffer with a specific value

• Implementation details

  1. Because this glClearTexImage function needs to specify different parameters depending on whether it is set to an int value or a float value.
  2. Scalability needs to be properly considered , but currently only int values ​​need to be filled, so you can simply write it in and change it later if there is any increase.

key code

• After filling the buffer with color, you need to fill the second buffer of the framebuffer with a specific value

  // 将渲染的东西放到帧缓冲中
  m_Framebuffer->Bind();
  RenderCommand::SetClearColor({
        
         0.1f, 0.1f, 0.1f, 1 });
  RenderCommand::Clear();
  
  /
  // 用-1填充帧缓冲的第二个颜色缓冲区
  m_Framebuffer->ClearAttachment(1, -1);
  

• specific fill function

  void OpenGLFramebuffer::ClearAttachment(uint32_t attachmentIndex, int value)
  {
        
        
      HZ_CORE_ASSERT(attachmentIndex < m_ColorAttachments.size());
  
      auto& spec = m_ColorAttachmentSpecifications[attachmentIndex];
      ///
      ///
      // 使用glClearTexImage函数
      glClearTexImage(m_ColorAttachments[attachmentIndex], 0, 		Utils::FramebufferTextureFormatToGLenum(spec.TextureFormat), GL_INT, &value);
  }
  
  static GLenum FramebufferTextureFormatToGLenum(FramebufferTextureFormat format) {
        
        
      switch (format)
      {
        
        
          case FramebufferTextureFormat::RGBA8:
              return GL_RGBA8;
          case FramebufferTextureFormat::RED_INTEGER:
              return GL_RED_INTEGER;
      }
      HZ_CORE_ASSERT(false);
      return 0;
  }
  

Effect

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