Enum FrameRatePreference 

pub enum FrameRatePreference {
    Auto,
    NoPreference,
    Exact(f32),
}

How the platform should vote the display’s frame rate on behalf of the app.

Compose apps get 120 Hz gameplay on a 120 Hz panel not by presenting faster but because HWUI votes a rate on the window while gestures run, content moves or the window redraws continuously, and clears it when they stop. A window that never votes is pinned by SurfaceFlinger’s cadence inference instead — which also throttles the app’s choreographer, so the inference reinforces itself. Auto reproduces the HWUI behaviour; the platform backends read it every frame and vote through the native window when the desired rate changes.

Variants

Auto

Ask for the panel’s fastest rate while FrameRateBoost holds, a quiet rate while frames arrive only intermittently, no preference when the scene is still. This is the default, matching what Compose/HWUI do for every app without the app’s involvement.

NoPreference

Never vote; the OS infers a rate from presentation cadence.

Exact(f32)

Always vote exactly this rate in Hz. Values <= 0 behave like FrameRatePreference::NoPreference.

Implementations

impl FrameRatePreference

pub const AUTO_QUIET_RATE_HZ: f32 = 60.0

The baseline Auto votes while frames arrive without a boost — the same rate HWUI’s NORMAL frame-rate category resolves to on phone panels. The quiet vote cannot simply be “no vote”: SurfaceFlinger infers a non-voting window’s rate from whatever cadence it last observed and pins it, so an app that ever ran the panel’s fast rate would stay there forever (measured on a Pixel 9 Pro, both directions).

pub fn desired_rate_hz( self, producing_frames: bool, boosted: bool, panel_max_hz: Option<f32>, ) -> f32

The rate the platform should vote right now, in Hz, where 0.0 means “clear the vote”. producing_frames is whether the frame loop has a frame scheduled, boosted what FrameRateBoost::boosted says, and panel_max_hz the display’s fastest supported rate when the platform knows it.

While boosted, Auto holds the boost even through moments with no frame scheduled: a gesture sequence crosses still screens (a tap lands, the old scene stops animating, the new one hasn’t started), and letting each of those instantly clear the vote flapped the display between the boost rate and no-vote several times per second on device. This mirrors SurfaceFlinger’s own touch boost, which also outlives the touch by seconds regardless of what the app presents in between.

Trait Implementations

impl Clone for FrameRatePreference

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 FrameRatePreference

impl Debug for FrameRatePreference

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

Formats the value using the given formatter.

impl Default for FrameRatePreference

fn default() -> Self

Returns the “default value” for a type.

impl PartialEq for FrameRatePreference

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for FrameRatePreference