OpenGL: preparing data to be sent to shaders confusion

Question

I'm a bit confused as to how to set up my application to send data to my shaders and be drawn. I know that I have to generate a VAO, bind it, generate buffer objects, bind them, populate it with data and create an attribute pointer to reference the data in the buffer object, because the openGL red book told me to... but I don't actually know what is happening in the process. could someone explain the process of this step by step and explain what is happening; to clear this up for me, and anybody else who doesn't quite understand this process. Also what does the VAO actually do? I know I can just reference the data in a buffer object with an attribute pointer and it will work fine, so what's the point in a VAO?

Answer 1

A Vertex Array Object (VAO) is an object which contains a group of Vertex Buffer Objects and is designed to store the information for a complete rendered object or a complete render batch. If you wouldn't use VAOs, for each batch you would have to bind all the VBOs one by one. With all VBOs in the batch in a VAO, you would just have to bind the VAO once instead of binding all the VBOs.

A Vertex Buffer Object (VBO) is a memory buffer in the high speed memory of your video card designed to hold information about vertices. VBOs can store information such as normals, texcoords, vertices, etc. This is why you have to let the shaders know whats inside the VBO using attribute pointers. VBOs offer substantial performance gains over immediate mode rendering primarily because the data resides in the video device memory rather than the system memory and so it can be rendered directly by the video device.

You have to bind the VBOs or VAOs to let OpenGL know what you are going to draw with the next draw call or that you are going to work with certain VBOs and tell OpenGL to have them ready for use.