Enum ScrollDelta 

pub enum ScrollDelta {
    PageDelta(f32, f32),
    LineDelta(f32, f32),
    PixelDelta(PhysicalPosition<f64>),
}

Scroll delta.

Deltas are in a Y-down coordinate system, and represent a ‘navigation’ direction; a positive Y value means that the viewport should move downward relative to the content.

For mouse wheel events, only LineDelta and PixelDelta are typical. For scroll deltas generated by scrollbars or other elements, PageDelta may be used (for example, when clicking in the well of the scrollbar).

Variants

PageDelta(f32, f32)

Page delta.

Page deltas are almost always synthetic, typically generated by clicking in the well of a scrollbar.

LineDelta(f32, f32)

Line delta.

PixelDelta(PhysicalPosition<f64>)

Pixel delta.

Implementations

impl ScrollDelta

pub fn to_pixel_delta( self, line_px: PhysicalPosition<f64>, page_px: PhysicalPosition<f64>, ) -> PhysicalPosition<f64>

Convert this scroll delta into a pixel delta using caller-provided scaling.

This is a policy hook: the caller chooses what a “line” or “page” means in pixels.

Example (physical pixel policy)

Convert line deltas into a pixel delta by choosing a line size in physical pixels:

use dpi::PhysicalPosition;
use ui_events::ScrollDelta;

let delta = ScrollDelta::LineDelta(0.0, -3.0);

// Policy: 1 line = 40 physical px vertically.
let line_px = PhysicalPosition { x: 0.0, y: 40.0 };
// Policy: 1 page = 800 physical px vertically (e.g. viewport height).
let page_px = PhysicalPosition { x: 0.0, y: 800.0 };

let px = delta.to_pixel_delta(line_px, page_px);
assert_eq!(px, PhysicalPosition { x: 0.0, y: -120.0 });

Scale factor and logical units

If your policy is expressed in logical/CSS pixels, apply your scale factor (device pixel ratio) before calling to_pixel_delta:

use dpi::PhysicalPosition;
use ui_events::ScrollDelta;

let delta = ScrollDelta::LineDelta(0.0, 1.0);
let dpr = 2.0; // from your platform/window

// Policy: 1 line = 16 CSS px vertically.
let line_px = PhysicalPosition { x: 0.0, y: 16.0 * dpr };
// Policy: 1 page = 800 physical px vertically.
let page_px = PhysicalPosition { x: 0.0, y: 800.0 };

let _px = delta.to_pixel_delta(line_px, page_px);

• ScrollDelta::PixelDelta is returned unchanged.
• ScrollDelta::LineDelta is multiplied by line_px per axis.
• ScrollDelta::PageDelta is multiplied by page_px per axis.

pub fn into_pixel_delta( self, line_px: PhysicalPosition<f64>, page_px: PhysicalPosition<f64>, ) -> Self

Convert this scroll delta into ScrollDelta::PixelDelta using caller-provided scaling.

Trait Implementations

impl Clone for ScrollDelta

fn clone(&self) -> ScrollDelta

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for ScrollDelta

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

Formats the value using the given formatter.

impl PartialEq for ScrollDelta

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Copy for ScrollDelta

impl StructuralPartialEq for ScrollDelta