Polyline flashing with weird shapes

[tqwewe]

I am trying to learn nannou, and I attempted to make a line that follows the y position of your mouse.

The line flickers as seen in the gif below:

I came up with the following source code:

extern crate nannou;

use nannou::prelude::*;

fn main() {
    nannou::run(model, event, view);
}

struct Model {
    y_positions: Vec<f32>,
}

fn model(app: &App) -> Model {
    // Start in `Wait` mode. In other words, don't keep looping, just wait for events.
    app.set_loop_mode(LoopMode::rate_fps(60.0));
    // Set a window title.
    app.main_window().set_title("`LoopMode` Demonstration");
    Model {
        y_positions: Vec::new(),
    }
}

fn event(app: &App, mut model: Model, event: Event) -> Model {
    match event {
        Event::Update(update) => {
            model.y_positions.push(app.mouse.y);
            if model.y_positions.len() > 300 / 5 {
                model.y_positions.remove(0);
            }
        }
        _ => (),
    }
    model
}

// Draw the state of your `Model` into the given `Frame` here.
fn view(app: &App, model: &Model, frame: Frame) -> Frame {
    let window = app.window_rect();
    let draw = app.draw();

    draw.background().color(BLUE);

    if model.y_positions.len() > 1 {
        let half_thickness = 0.5;
        let vertices = (0..model.y_positions.len())
            .map(|i| pt2(((i as f32) * 5.0) - window.w() / 2.0, model.y_positions[i]))
            .enumerate()
            .map(|(i, p)| {
                let r = 1.0;
                let g = 0.0;
                let b = 0.0;
                let rgba = nannou::color::Rgba::new(r, g, b, 1.0);
                geom::vertex::Rgba(p, rgba)
            });

        draw.polyline().vertices(half_thickness, vertices);
    }

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

    frame
}

Is this something I am doing wrong, or a bug with nannou?

[mitchmindtree]

Hey @acidic9 thanks for the issue!

You are doing nothing wrong at all, this is entirely nannou's fault! We're aware of this bug #185 however rather than spending time on fixing it, we have a plan to switch to using the lyon crate under the hood to solve this and a whole suite of other issues related to 2D graphics. Lyon is an extremely impressive crate with high quality tools for tesselating all kinds of 2D geometry like curves, lines with interesting joins, etc including support for GPU tesselation. See #253. This will be a top priority for us after we land 0.9 in the coming weeks (see #240).

I hope this helps and that this isn't causing you too many problems!