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use crate::*;

const THETA_MIN: f32 = 3.0 / 2.0 * std::f32::consts::PI;
const THETA_MAX: f32 = 7.0 / 2.0 * std::f32::consts::PI;

fn lerp(x: f32, a: f32, b: f32) -> f32 {
    (1.0 - x) * a + x * b
}

/// Knob for controlling a 0 to 1 floating point parameter.
pub fn knob(value: impl Binding<f32>) -> impl View {
    zstack((
        circle()
            .color(CLEAR_COLOR)
            .drag(move |cx, off, _state, _mouse_button| {
                value.with_mut(cx, |v| *v = (*v + (off.x + off.y) / 400.0).clamp(0.0, 1.0));
            }),
        canvas(move |cx, sz, vger| {
            let c = sz.center();
            let r = sz.width().min(sz.height()) / 2.0;

            let paint = vger.color_paint(CONTROL_BACKGROUND);

            vger.stroke_arc(c, r, 2.0, 0.0, std::f32::consts::PI, paint);

            let paint = vger.color_paint(AZURE_HIGHLIGHT);
            let a0 = lerp(*value.get(cx), THETA_MAX, THETA_MIN);
            let a1 = THETA_MAX;

            let theta = -(a0 + a1) / 2.0 + std::f32::consts::PI;
            let ap = (a0 - a1).abs() / 2.0;

            vger.stroke_arc(c, r, 2.0, theta, ap, paint);
        }),
    ))
}