Trait ScrollExt

Source

pub trait ScrollExt: Sized {
    // Required methods
    fn offset(self, signal: RwSignal<f32>) -> Self;
    fn follow_end(self, signal: RwSignal<bool>) -> Self;
}

Expand description

Controls the offset of a scroll view through a signal.

Import the trait to use it:

use smudge_core::reactive::RwSignal;
use smudge_core::widget::panel;
use smudge_widgets::{ScrollExt, column, scroll};

let offset = RwSignal::new(0.0);
let view = scroll(column().child(panel())).offset(offset);

Required Methods§

Source

fn offset(self, signal: RwSignal<f32>) -> Self

Scrolls with signal: the view reads the signal for its offset, so a write from anywhere moves the content, clamped to the content’s size.

The wheel writes the same signal, and the view writes the clamped offset back to it, so the view, the thumb and the signal stay in step.

Source

fn follow_end(self, signal: RwSignal<bool>) -> Self

Keeps the view at the end of its content while signal reads true.

While it follows, every frame that grows the content leaves the view pinned to the end in the same frame, so a line appended to a log is already in view. The core applies that pin after each layout pass, where the painted heights the offset signal round-trips through are one frame old. The view writes the painted end back to the offset signal, so a signal set with ScrollExt::offset tracks the position on screen and catches up one frame after a frame that grew the content.

The signal is also where the view reports where the user is: any wheel step that moves the view up from the end writes false, and a step down that lands within four logical pixels of the end writes true. Writing true from the application jumps to the end. A view that starts following with content shorter than itself stays at offset zero until the content grows past it.

Give the signal to one view. Two views that share it pin and release together, and a wheel step over either one decides for both.

While it follows, the offset signal is the view’s to write: a write from the application is overwritten, and the way to move the view is to write false first.

use smudge_core::geometry::Color;
use smudge_core::reactive::{RwSignal, prelude::*};
use smudge_core::style::px;
use smudge_core::widget::panel;
use smudge_widgets::{ScrollExt, column, scroll};

let following = RwSignal::new(true);
let view = scroll(
    column().child(panel().height(px(400.0)).background(Color::WHITE)),
)
.follow_end(following.clone())
.height(px(120.0));

// The view shows the end of the content from the first frame on,
// and stays there while the content grows.
following.set(false);