Enum NarrowPolicy 

#[non_exhaustive]
pub enum NarrowPolicy {
    Combined,
    AutoOnModeset,
    PerCrtc,
}

How to split a frame across the outputs it touches.

The policy shapes the groups partition_for_policy returns; each group is one atomic commit for the caller to make.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Combined

Never split: one group, so one atomic commit, for every engaged scene.

The only policy that makes a multi-output frame atomic — either every output shows the new frame or none does. What it costs is that one output’s refusal takes the others down with it, and that a modeset anywhere forces ALLOW_MODESET on the whole commit.

AutoOnModeset

Split only when the outputs disagree about modesetting.

The default, and the reason the policy exists. A modeset is expensive and can blank an output; a steady frame is neither. Committing them together makes every steady output pay the modeset’s cost, so when the set is mixed they go separately — modeset first, since a steady frame on an output that is about to be reconfigured is wasted work. When every engaged scene agrees, one commit, and the atomicity is kept.

PerCrtc

One commit per engaged scene, always.

Gives up cross-output atomicity to contain failure: an output that refuses its frame does not stop the others showing theirs. For a caller that would rather have three screens right and one wrong than four screens stale.

Trait Implementations

impl Clone for NarrowPolicy

fn clone(&self) -> Self

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for NarrowPolicy

impl Debug for NarrowPolicy

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Default for NarrowPolicy

fn default() -> Self

Returns the “default value” for a type.

impl Eq for NarrowPolicy

impl PartialEq for NarrowPolicy

fn eq(&self, other: &Self) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for NarrowPolicy