Crate drmkit_present 

The present spine: getting rendered frames onto a display, repeatedly.

Port of src/present/ from drm-cxx @ 4a0b64a, less the GPU producers.

Where drmkit_scene answers “what goes on which plane this frame”, this crate answers the questions around it: which buffer to draw into, how much of it needs redrawing, and whether the frame is worth submitting at all.

Why it is a separate crate

A producer that renders on the GPU needs EGL or Vulkan; one that writes pixels with the CPU needs neither. Keeping the spine core-only means a GPU-less build — a kiosk, a test rig, an instrument panel — links no graphics stack at all. The producers that do live in their own crates and load their libraries at runtime.

Not here yet

Being built up. BufferRing, negotiate and FrameEconomy are in; ScanoutBackend, DumbScanoutSink and DumbRingSource follow, and the GBM, GL and Vulkan producers are separate crates after that.

Structs

BackendConfig

How to build a scanout backend.

BufferRing

A producer-agnostic pool of scanout slots with buffer age and damage accumulation.

Config

How a sink is configured.

DumbRingSource

A ring of CPU-mapped dumb buffers, presented as a scene layer’s source.

DumbScanoutSink

A software present path: hand it a finished CPU frame, it puts it on screen.

FrameEconomy

The per-frame present decision, and what it has decided so far.

GbmScanoutProducer

Allocates scanout buffers straight from the DRM node’s GBM device.

Lease

A slot handed to the producer for the next frame.

Rect

A damage rectangle, in buffer pixels.

ScanoutBackend

One output, one layer, and everything between a producer and the screen.

Enums

FrameAction

What the present loop should do with this frame.

PaintError

What went wrong painting a frame.

PresentError

What went wrong presenting a frame.

ProducerError

Why a producer could not hand over a buffer.

Repaint

What a reused slot must repaint before its contents are a correct frame.

RestorePolicy

What to leave on screen when the backend goes away.

VrrPolicy

When to ask for variable refresh.

Constants

DEFAULT_PREFERENCE

The default preference order: most colour depth first, 16-bit last.

Traits

ScanoutProducer

Something that allocates the buffers a scanout path presents.

Functions

negotiate

Intersect what a producer can export with what a plane can scan out, and rank the survivors.

negotiate_for_format

As negotiate, taking the plane’s modifiers from a FormatTable for one fourcc.

negotiate_scanout_format

The first format in preferred that a plane on crtc_id can scan out.