// 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;
    };
};