Published Dec 11, 2019
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OpenGL is mainly considered an API that provides us with a large set of functions that we can use to manipulate graphics and images. However, OpenGL by itself is not an API, but merely a specification.
OpenGL is by itself a large state machine: a collection of variables that define how OpenGL should currently operate. The state of OpenGL is commonly referred to as the OpenGL context. When using OpenGL, we often change its state by setting some options, manipulating some buffers and then render using the current context.
Whenever we tell OpenGL that we now want to draw lines instead of triangles for example, we change the state of OpenGL by changing some context variable that sets how OpenGL should draw. As soon as we change context by telling OpenGL it should draw lines, that next drawing commands will now draw lines instead of triangles.
When working in OpenGL we will come across several state-changing functions that change the context and several state-using functions that perform some operations based on the current state of OpenGL.
An object in OpenGL is a collection of options that represents a subset of of OpenGL’s state. For example, we could have an object that represents the settings of the drawing window; we could then set its size, how many colors it supports and so on.