What does overdraw refer to in relation to performance optimization?

Overdraw refers specifically to the rendering of the same pixel multiple times during the rendering process. This phenomenon occurs when multiple layers of geometry overlap on the screen, leading to the GPU repeatedly processing the same pixel for each layer. As a result, overdraw can significantly degrade performance because it requires the GPU to do extra work that does not contribute to the final image seen by the player. High levels of overdraw can lead to reduced frame rates and increased rendering times, making performance optimization critical in game design, especially in scenes with complex visuals or numerous overlapping elements. Reducing overdraw involves techniques such as simplifying shader calculations, optimizing geometry, and using appropriate occlusion culling methods to ensure that only visible pixels are rendered, which ultimately leads to a smoother user experience.