Add Ui::with_visual_transform

[lucasmerlin]

• I have followed the instructions in the PR template

This allows you to transform widgets without having to put them on a new layer.
Example usage:

Bildschirmaufnahme.2024-09-01.um.22.32.42.mov

use eframe::egui;
use eframe::egui::{Button, Frame, InnerResponse, Label, Pos2, RichText, UiBuilder, Widget};
use eframe::emath::TSTransform;
use eframe::NativeOptions;
use egui::{CentralPanel, Sense, WidgetInfo};

pub fn main() -> eframe::Result {
    eframe::run_simple_native("focus test", NativeOptions::default(), |ctx, _frame| {
        CentralPanel::default().show(ctx, |ui| {
            let response = ui.ctx().read_response(ui.next_auto_id());

            let pressed = response
                .as_ref()
                .is_some_and(|r| r.is_pointer_button_down_on());

            let hovered = response.as_ref().is_some_and(|r| r.hovered());

            let target_scale = match (pressed, hovered) {
                (true, _) => 0.94,
                (_, true) => 1.06,
                _ => 1.0,
            };

            let scale = ui
                .ctx()
                .animate_value_with_time(ui.id().with("Down"), target_scale, 0.1);

            let mut center = response
                .as_ref()
                .map(|r| r.rect.center())
                .unwrap_or_else(|| Pos2::new(0.0, 0.0));
            if center.any_nan() {
                center = Pos2::new(0.0, 0.0);
            }

            let transform = TSTransform::from_translation(center.to_vec2())
                * TSTransform::from_scaling(scale)
                * TSTransform::from_translation(-center.to_vec2());

            ui.with_visual_transform(transform, |ui| {
                Button::new(RichText::new("Yaaaay").size(20.0))
                    .sense(Sense::click())
                    .ui(ui)
            });
        });
    })
}