egui-112-keypress-move-circle-with-velocity

This is a simple example of keypressing to change the velocity of a circle, causing it to move around the screen.

Source

• src/main.rs
• Project Directory

Screenshots

Description

When creating the ExampleApp struct, we add two values to hold the position of the circle, and one value to hold the size, and one value for the color.

struct ExampleApp {
    vx: f32,
    vy: f32,
    vs: f32,
    cx: f32,
    cy: f32,
    cs: f32,
    cc: Color32,
}

These values need initialized in the Default trait implementation. Rust will call the default() function and expect to get a fully initialized structure back as the return value.

impl Default for ExampleApp {
    fn default() -> Self {
        Self {
            vx: 0.0,
            vy: 0.0,
            vs: 0.0,
            cx: 100.0,
            cy: 100.0,
            cs: 50.0,
            cc: Color32::BLUE,
        }
    }
}

We use ctx.input().key_pressed() to check if a specific key is pressed everytime update() is called. If the key is pressed, we change one of our values.

W,A,S,D to move around, and UP,DOWN to change size, C,O to change color.

fn update(&mut self, ctx: &egui::Context, frame: &mut eframe::Frame) {
    
    ctx.set_pixels_per_point(1.5);

    if ctx.input().key_pressed(egui::Key::W) {
        self.vy += -20.00
    }
    if ctx.input().key_pressed(egui::Key::S) {
        self.vy += 20.00
    }
    if ctx.input().key_pressed(egui::Key::A) {
        self.vx += -20.00
    }
    if ctx.input().key_pressed(egui::Key::D) {
        self.vx += 20.00
    }
    if ctx.input().key_pressed(egui::Key::ArrowUp){
        self.vs += 5.0
    }
    if ctx.input().key_pressed(egui::Key::ArrowDown){
        self.vs += -5.0
    }

    egui::CentralPanel::default().show(ctx, |ui| {
        if ui.button("Quit").clicked() {
            frame.quit()
        };

        let painter = ui.painter();

        painter.circle(
            egui::Pos2{x:self.cx,y:self.cy}, 
            self.cs, 
            self.cc, 
            Stroke{width: 2.0, color: Color32::from_rgb(255, 255, 255)}
        );
    });
}