And what is a Vertex Buffer? A Vertex Buffer is another data structure that packs all the vertices that need to be rendered, by using vertex arrays, and makes that information available to the shaders in the graphics pipeline. And how do you describe a point in a 3D space? By specifying its x, y and z coordinates. But, what is a vertex? A vertex is a data structure that describes a point in 2D or 3D space. The rendering starts taking as its input a list of vertices in the form of Vertex Buffers. The following picture depicts a simplified version of the OpenGL programmable pipeline: In this model, the different steps that compose the graphics pipeline can be controlled or programmed by using a set of specific programs called shaders. OpenGL 2.0 introduced the concept of programmable pipeline. The graphics pipeline was composed of these steps: Thus, the effects and operations that could be applied were limited by the API itself (for instance, “set fog” or “add light”, but the implementation of those functions were fixed and could not be changed). The programmer was constrained to the set of functions available for each step. This model employed a set of steps in the rendering process which defined a fixed set of operations. First versions of OpenGL employed a model which was called fixed-function pipeline. The sequence of steps that ends up drawing a 3D representation into your 2D screen is called the graphics pipeline. Modern OpenGL lets you think in one problem at a time and it lets you organize your code and processes in a more logical way. It is actually simpler and much more flexible. Let me give you an advice for those of you that think that way. You may end up thinking that drawing a simple shape to the screen should not require so many concepts and lines of code.
If you are used to older versions of OpenGL, that is fixed-function pipeline, you may end this chapter wondering why it needs to be so complex. In this chapter we will learn the processes that takes place while rendering a scene using OpenGL.
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