Fragment (computer graphics) in the context of Shader

A z-buffer, also known as a depth buffer, is a type of data buffer used in computer graphics to store the depth information of fragments. The values stored represent the distance to the camera, with 0 being the closest. The encoding scheme may be flipped with the highest number being the value closest to camera.

In a 3D-rendering pipeline, when an object is projected on the screen, the depth (z-value) of a generated fragment in the projected screen image is compared to the value already stored in the buffer (depth test), and replaces it if the new value is closer. It works in tandem with the rasterizer, which computes the colored values. The fragment output by the rasterizer is saved if it is not overlapped by another fragment.

In computer graphics, a shader is a programmable operation which is applied to data as it moves through the rendering pipeline. Shaders can act on data such as vertices and primitives—to generate or morph geometry—and fragments –to calculate the values in a rendered image.

Shaders can execute a wide variety of operations and can run on different types of hardware. In modern real-time computer graphics, shaders are run on graphics processing units (GPUs) –dedicated hardware which provides highly parallel execution of programs. As rendering an image is embarrassingly parallel, fragment and pixel shaders scale well on SIMD hardware. Historically, the drive for faster rendering has produced highly-parallel processors which can in turn be used for other SIMD amenable algorithms. Such shaders executing in a compute pipeline are commonly called compute shaders.