Rendering pipeline

In 3D computer graphics, the graphics pipeline or rendering pipeline refers to the sequence of steps used to create a 2D raster representation of a 3D scene. Plainly speaking, once a 3D model has been created, for instance in a video game or any other 3D computer animation, the graphics pipeline is the process of turning that 3D model into what the computer displays. In the early history of 3D computer graphics, fixed purpose hardware was used to speed up the steps of the pipeline through a fixed-function pipeline. Later, the hardware evolved, becoming more general purpose, allowing greater flexibility in graphics rendering as well as more generalized hardware, and allowing the same generalized hardware to perform not only different steps of the pipeline, like in fixed purpose hardware, but even in limited forms of general purpose computing. As the hardware evolved, so did the graphics pipelines, the OpenGL, and DirectX pipelines, but the general concept of the pipeline remains the same.

The 3D pipeline usually refers to the most common form of computer 3D rendering, 3D polygon rendering, distinct from raytracing, and raycasting. In particular, 3D polygon rendering is similar to raycasting. In raycasting, a ray originates at the point where the camera resides, if that ray hits a surface, then the color and lighting of the point on the surface where the ray hit is calculated. In 3D polygon rendering the reverse happens, the area that is in view of the camera is calculated, and then rays are created from every part of every surface in view of the camera and traced back to the camera.

Computers began undergoing a significant change in recent years with the introduction of a separate video card and the rise of hardware accelerated graphics. This has led to the need for a programmable graphics pipeline which can be manipulated by shaders. Since the introduction of the programmable graphics pipeline most fixed-function pipeline implementations have become obsolete, such as OpenGL's immediate mode, or Direct3D's built in hardware Transform, clipping, and lighting.

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