zbuffer

A z-buffer, also known as a depth buffer, is a per-pixel storage used in 3D rendering to record the depth of the closest object at each image sample. It is essential for hidden-surface removal, enabling the renderer to determine which surfaces are visible from the camera.

During rasterization, each generated fragment yields a depth value z. This value is compared against the current value stored in the depth buffer for that screen-space location. If the new fragment is closer to the camera (typically a smaller depth value, using a 0–1 range), the depth buffer is updated and the fragment's color is written to the color buffer; otherwise the fragment is discarded. The process is repeated per frame, with the depth buffer cleared at the start.

Depth buffers are usually paired with a color buffer and can use various bit depths, commonly 16, 24, or 32 bits. Depth values are often stored non-linearly after projection, which concentrates precision near the near plane. Improper choice of near and far planes can cause z-fighting, where two surfaces at similar depths compete for visibility.

Hardware implementations perform the depth test in parallel on the GPU and may include early depth testing to avoid shading fragments that fail the test. Some systems use additional techniques such as a hierarchical or logarithmic depth buffer to improve performance and precision.

Limitations of z-buffering include finite precision leading to artifacts, and memory usage proportional to the display resolution. Despite limitations, z-buffering remains a standard approach for real-time 3D rendering due to its generality and efficiency.