Small Steps II — Making Things

Changing once per key press

Make one change for each new key press.

What you will learn

key_pressed reports a new press. Distinguish it from key_down, which is true every frame while a key remains held.

Try it

void small_main()
{
    Window window;
    window.open(640, 480);

    bool is_red = true;

    while (window.is_open())
    {
        if (window.key_pressed(Key::Space))
            is_red = !is_red;

        window.clear(Black);

        if (is_red)
            window.fill_circle(320, 240, 60, Red);
        else
            window.fill_circle(320, 240, 60, Blue);

        window.show();
    }
}

When Space is newly pressed, is_red = !is_red; toggles true and false. That value chooses is_red or blue. Hold Space, release it, and press it again.

key_released reports the moment a key is released. Down is convenient for movement; Pressed is convenient for a single change.

Exercise

Alternate the circle's radius between 20 and 60 each time Space is pressed. It must not keep changing while Space is held.

void small_main()
{
    Window window;
    window.open(640, 480);

    bool is_big = false;

    while (window.is_open())
    {
        // Toggle is_big when Space is pressed.

        window.clear(Black);

        if (is_big)
            window.fill_circle(320, 240, 60, Yellow);
        else
            window.fill_circle(320, 240, 20, Yellow);

        window.show();
    }
}

Hint

Use key_pressed(Key::Space) and a bool variable to alternate between two states.

void small_main()
{
    Window window;
    window.open(640, 480);

    bool is_big = false;

    while (window.is_open())
    {
        if (window.key_pressed(Key::Space))
            is_big = !is_big;

        window.clear(Black);

        if (is_big)
            window.fill_circle(320, 240, 60, Yellow);
        else
            window.fill_circle(320, 240, 20, Yellow);

        window.show();
    }
}