module main

import gg
import gx

const rate = f32(1) / 60 * 10

struct App {
mut:
    gg   &gg.Context = unsafe { nil }
    anim &Anim       = unsafe { nil }
}

struct Anim {
mut:
    time    f32
    reverse bool
}

fn (mut anim Anim) advance() {
    if anim.reverse {
        anim.time -= 1 * rate
    } else {
        anim.time += 1 * rate
    }
    // Use some arbitrary value that fits 60 fps
    if anim.time > 80 * rate || anim.time < -80 * rate {
        anim.reverse = !anim.reverse
    }
}

fn main() {
    mut app := &App{
        gg: 0
        anim: &Anim{}
    }
    app.gg = gg.new_context(
        bg_color: gx.rgb(174, 198, 255)
        width: 600
        height: 400
        window_title: 'Animated cubic Bézier curve'
        frame_fn: frame
        user_data: app
    )
    app.gg.run()
}

fn frame(mut app App) {
    time := app.anim.time

    p1_x := f32(200.0)
    p1_y := f32(200.0) + (10 * time)

    p2_x := f32(400.0)
    p2_y := f32(200.0) + (10 * time)

    ctrl_p1_x := f32(200.0) + (40 * time)
    ctrl_p1_y := f32(100.0)
    ctrl_p2_x := f32(400.0) + (-40 * time)
    ctrl_p2_y := f32(100.0)

    points := [p1_x, p1_y, ctrl_p1_x, ctrl_p1_y, ctrl_p2_x, ctrl_p2_y, p2_x, p2_y]

    app.gg.begin()
    app.gg.draw_cubic_bezier(points, gx.blue)
    app.gg.end()
    app.anim.advance()
}