Nannou - How to draw a pie (part of an ellipse)?

Question

I'm new to the rust library Nannou and I'm trying to draw pie chart. I know that in javascript you can specify the amount of the ellipse via:

ctx.ellipse(x, y, radiusX, radiusY, rotation, startAngle, endAngle, anticlockwise);

I couldn't however find anything similar in Nannou like:

draw.ellipse().angle(PI);

Answer 1

The nannou::draw::primitive::ellipse::Ellipse does not support sections.

However you can use the Section from nannou::geom::Ellipse.

Here is a simple example:

use nannou::{
    geom::{Ellipse, Tri},
    prelude::*,
};

fn main() {
    nannou::sketch(view).run()
}

fn view(app: &App, frame: Frame) {
    let draw = app.draw();
    let win = app.window_rect();

    draw.background().color(CORNFLOWERBLUE);

    let t = app.time;

    let radius = if win.h() < win.w() {
        win.w() / 3f32
    } else {
        win.h() / 3f32
    };

    let section = Ellipse::new(Rect::from_x_y_w_h(0f32, 0f32, radius, radius), 120f32)
        .section(0f32, t.sin() * 2f32 * std::f32::consts::PI);

    let triangles = section.trangles();
    let mut tris = Vec::new();
    for t in triangles {
        tris.push(Tri([
            [t.0[0][0], t.0[0][1], 0f32],
            [t.0[1][0], t.0[1][1], 0f32],
            [t.0[2][0], t.0[2][1], 0f32],
        ]));
    }

    draw.mesh().tris(tris.into_iter()).color(RED);

    draw.to_frame(app, &frame).unwrap();
}