Module uefi::proto::console::gop

Graphics output protocol.

The UEFI GOP is meant to replace existing VGA hardware interfaces. It can be used in the boot environment as well as at runtime, until a high-performance driver is loaded by the OS.

The GOP provides access to a hardware frame buffer and allows UEFI apps to draw directly to the graphics output device.

The advantage of the GOP over legacy VGA is that it allows multiple GPUs to exist and be used on the system. There is a GOP implementation for every unique GPU in the system which supports UEFI.

This protocol can be used after boot services are exited.

Definitions

All graphics operations use a coordinate system where the top-left of the screen is mapped to the point (0, 0), and y increases going down.

Rectangles are defined by their top-left corner, and their width and height.

The stride is understood as the length in bytes of a scan line / row of a buffer. In theory, a buffer with a width of 640 should have (640 * 4) bytes per row, but in practice there might be some extra padding used for efficiency.

Frame buffers represent the graphics card’s image buffers, backing the displays.

Blits (block transfer) can do high-speed memory copy between the frame buffer and itself, or to and from some other buffers.

Blitting

On certain hardware, the frame buffer is in a opaque format, or cannot be accessed by the CPU. In those cases, it is not possible to draw directly to the frame buffer. You must draw to another buffer with a known pixel format, and then submit a blit command to copy that buffer into the back buffer.

Blitting can also copy a rectangle from the frame buffer to another rectangle in the frame buffer, or move data out of the frame buffer into a CPU-visible buffer. It can also do very fast color fills.

The source and destination rectangles must always be of the same size: no stretching / squashing will be done.

Animations

UEFI does not mention if double buffering is used, nor how often the frame buffer gets sent to the screen, but it’s safe to assume that the graphics card will re-draw the buffer at around the monitor’s refresh rate. You will have to implement your own double buffering if you want to avoid tearing with animations.

Structs

BltPixel	Format of pixel data used for blitting.
FrameBuffer	Direct access to a memory-mapped frame buffer
GraphicsOutput	Provides access to the video hardware’s frame buffer.
Mode	Represents a graphics mode compatible with a given graphics device.
ModeInfo	Information about a graphics output mode.
PixelBitmask	Bitmask used to indicate which bits of a pixel represent a given color.

Enums

BltOp	Blit operation to perform.
BltRegion	Region of the BltBuffer which we are operating on
PixelFormat	Represents the format of the pixels in a frame buffer.