// Feed pointer state once per event-loop iteration. Activate on release inside,
// only after a press that began inside. No native/window dependency.
struct Button {
    int x, y, width, height;
    u8[~] !label;
    bool !enabled = true, !hovered = false, !pressed = false;
    bool !_held = false, !_armed = false;
    new Button = { int px, int py, int w, int h, u8[~] text ->
        x = px; y = py; width = w; height = h; label = text;
    };
    val contains = { i64 px, i64 py ->
        if( width <= 0 || height <= 0 ) return false;
        i64 right = x, bottom = y; right += width; bottom += height;
        if( px < x || py < y || px >= right || py >= bottom ) return false;
        return true;
    };
    val update = { i64 px, i64 py, bool down ->
        hovered = false;
        if( enabled ) hovered = contains(px,py);
        if( !enabled ) _armed = false;
        if( down && !_held ) _armed = hovered;
        var clicked = false;
        if( !down ) if( _held ) if( _armed ) if( hovered ) clicked = true;
        if( !down ) _armed = false;
        _held = down;
        pressed = false;
        if( down ) if( _armed ) if( hovered ) pressed = true;
        return clicked;
    };
    val draw = { !sys.draw.Canvas screen, int scale, u32 foreground, u32 background, u32 active ->
        screen.fillRect(x,y,width,height,enabled && (hovered || pressed) ? active : background);
        screen.rect(x,y,width,height,2,enabled ? foreground : active);
        if( scale > 0 ) {
            i64 textWidth = label#; textWidth = (textWidth*4-1)*scale;
            if( textWidth <= width-8 && 5*scale <= height-8 )
                screen.text(x+(width-textWidth)/2,y+(height-5*scale)/2+(pressed ? 1 : 0),
                    label,scale,enabled ? foreground : active);
        }
        return self;
    };
};