Struct Density 

pub struct Density { /* private fields */ }

The device pixel grid a layout measures against: how many device pixels a layout point is worth, and how the platform converts a text size.

This is Compose’s Density, and local_density is its LocalDensity.

Read it in a composable through density, which subscribes to the composition local rather than to process-wide state, so a subtree given its own density recomposes only what read it. Tests and goldens construct one directly so a measurement does not depend on the machine it runs on.

Implementations

impl Density

pub fn from_host() -> Self

The grid the host installed on this shell.

This is the composition local’s default, not the way a composable should read the density – use density for that, so a subtree provided its own grid is honoured.

pub fn new(density: f32, font_scale: f32) -> Self

A grid stated outright, for a test or a golden. The setting is taken as a plain multiplier, which is what it is wherever the platform reports no conversion of its own.

pub fn with_curve(density: f32, font_scale: FontScaleCurve) -> Self

A grid whose text size follows the platform’s own Sp conversion rather than a multiplier. See crate::font_scale.

pub fn density(self) -> f32

Device pixels per layout point.

pub fn font_scale(self) -> f32

The user’s text size setting.

pub fn font_scale_curve(self) -> FontScaleCurve

The conversion the platform performs for a size in Sp.

pub fn dp(self, value: f32) -> f32

Dp.roundToPx(), expressed back in points: a dp length snapped to the whole device pixel Compose would give it.

pub fn sp(self, value: f32) -> f32

A text size in scale-independent pixels, snapped the same way.

Anything that must not move when the user changes their text size is measured with Density::dp instead — that is the whole difference between the two.

pub fn round(self, value: f32) -> f32

A length snapped to the nearest whole device pixel, exact halves up.

pub fn floor(self, value: f32) -> f32

A length snapped down to a whole device pixel.

pub fn ceil(self, value: f32) -> f32

A length snapped up to a whole device pixel.

This is what a line box does with its own height, and what a container does with a content size it must not clip.

pub fn to_px(self, points: f32) -> f32

Points to device pixels.

pub fn centre(self, available: f32, content: f32) -> f32

Centres content in available the way Compose does: on a whole pixel.

Arrangement.Center measures every child in whole pixels and rounds the leading gap before placing any of them, so a column whose content is an odd number of pixels tall starts on a pixel boundary rather than across one. Halving in floats instead is the single easiest way to soften every edge in a row.

Trait Implementations

impl Clone for Density

fn clone(&self) -> Density

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Density

impl Debug for Density

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

Formats the value using the given formatter.

impl Default for Density

fn default() -> Self

Returns the “default value” for a type.

impl PartialEq for Density

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Density