Mode setting

Mode setting is a software operation that activates a display mode (screen resolution, color depth, and refresh rate) for a computer's display controller by using VESA BIOS Extensions or UEFI Graphics extensions (on more modern computers).

The display mode is set by the kernel. In user-space mode-setting (UMS), the display mode is set by a user-space process.

Kernel mode-setting is more flexible and allows displaying of an error in the case of a fatal system error in the kernel, even when using a user-space display server.

User-space mode setting would require superuser privileges for direct hardware access, so kernel-based mode setting shuns such requirement for the user-space graphics server.

On the hardware side, the GPU consists of multiple components, among which are render engine, i.e. the component of the GPU responsible for executing OpenGL/Vulkan commands, and the display engine, i.e. the component of the GPU responsible for sending a "video stream" to the screen, as opposed to the part performing rendering.

To improve performance, many GPUs come with a feature called hardware planes. Planes can make the display engine perform the composition. This is called direct scan-out and allows the compositor to avoid copying entirely. libliftoff is a library making better use of such hardware ability.

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