Struct RetainedPlacement 

pub struct RetainedPlacement {
    pub linear: [f64; 4],
    pub translation: (f64, f64),
}

Where a retained body lands on the device grid: the composed transform its local coordinates are mapped through, split into the linear part and the translation.

A page holds the body rasterized under one placement. Another placement can be served from it only when the linear parts agree — the same scale, rotation and skew, so the page’s pixels are the pixels the body would draw there — and the translations differ by a move a 1:1 composite can make (Self::offset_to).

Fields

linear: [f64; 4]

The transform’s linear part, [a, b, c, d] in kurbo’s coefficient order.

translation: (f64, f64)

The transform’s translation, in device pixels.

Implementations

impl RetainedPlacement

pub const LINEAR_EPSILON: f64 = 1e-6

How far apart two linear parts may be and still be read as one: well below anything a scale animation or a device-scale change produces, and well above the rounding a transform recomposed from the same factors accumulates.

pub fn of(transform: Affine) -> Self

The placement transform describes.

pub fn offset_to(&self, other: &Self) -> Option<(i32, i32)>

The whole-pixel move from self to other, or None when the two differ in anything but their translation.

A fractional move is rounded to the nearest whole pixel: a composite is a 1:1 copy of the page’s texels and cannot land between them, so a body sliding by a fraction of a pixel per frame is drawn at most half a pixel from where an inline lowering would rasterize it. A whole-pixel move (the common case of a scroll or a pixel-snapped transition) is exact.

pub fn extent(&self, rect: Rect) -> (u32, u32)

The device extent rect covers under this placement, per axis, rounded to whole pixels — the extent the resident-key ledger reports.

pub fn scale(&self) -> f32

The uniform scale this placement rasterizes at — the square root of the linear part’s determinant, which is the device scale for an axis-aligned body and the presentation scale folded into it.

Trait Implementations

impl Clone for RetainedPlacement

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 RetainedPlacement

impl Debug for RetainedPlacement

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

Formats the value using the given formatter.

impl PartialEq for RetainedPlacement

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for RetainedPlacement