An OpenGL vertex buffer is a memory area on a graphics card used for fast access to vertices and their properties. It can be used to create a vertex buffer object for rendering 3D objects. The buffer can be allocated as any data structure and does not need to be on the graphics card. Immediate mode rendering does not require a vertex buffer. When converted to a vertex buffer object, the buffer is optimized for drawing and stored in graphics card memory.
An Open Graphics Library® (OpenGL®) vertex buffer is an area of computer memory often located directly on a graphics card that allows very fast access to a set of vertices and their properties. Most often, an OpenGL® vertex buffer is used to create a vertex buffer object (VBO), allowing objects within a three-dimensional (3D) scene to be rendered as part of a display list and not in immediate mode. Occasionally, however, a vertex buffer outside a VBO can be used to store information about an object or to facilitate transformations on complex models. It should be noted that a vertex buffer does not need to be placed in graphics card memory, because it can be allocated as any data structure. If the OpenGL® vertex buffer will be used as part of a VBO, the graphics card used must support the special OpenGL® VBO extension to ensure that the buffer is placed in graphics memory.
At its most basic level, an OpenGL® vertex buffer is just a simple buffer, an allocated area of memory where data can be stored. Becomes a vertex buffer when an array of vertices is stored in it. An OpenGL® vertex array is an array of data structures that define all the properties of individual vertices. This information can include the X, Y and Z positions of the vertex in the 3D scene, the color of the vertex, the normal and other properties.
In immediate mode rendering, OpenGL® commands are executed directly as soon as they are called from within a program. In these cases it is not necessary to have an array of vertices, since the commands to place and draw a vertex can be given directly to the hardware, although this can cause serious performance problems. For non-immediate mode rendering, information about a 3D object or model must first be placed in a vertex array so that it has a structure that OpenGL® can easily interpret; that array must then be stored in a special area of memory known as an OpenGL® vertex buffer.
By itself, the vertex buffer doesn’t necessarily have any special attributes other than being a complete collection of information used to draw an object. When the OpenGL® vertex buffer is converted to an OpenGL® vertex buffer object via the OpenGL extension, however, a special sequence of events occurs to help optimize the drawing of the object defined in the vertex buffer. That is, the buffer is allocated and stored in graphics card memory, on the server side of the client-server configuration used by OpenGL®. Some calculations can even be done ahead of the VBO so it can be done as fast as possible. Outside of a VBO, a normal vertex buffer usually doesn’t get this treatment and can be allocated and used like any other data type.
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