rect method
Implementation
void rect( double x, double y, double w, double h, [double? scale] ){
_p!.style = ui.PaintingStyle.stroke;
_p!.strokeWidth = _canvasEnv._strokeWidth;
_p!.color = ui.Color.fromARGB( _canvasEnv._colorA, _canvasEnv._colorR, _canvasEnv._colorG, _canvasEnv._colorB );
if( scale == null ){
_c!.drawRect( ui.Rect.fromLTWH( x + 0.5, y + 0.5, w, h ), _p! );
} else {
_c!.drawRect( ui.Rect.fromLTWH( (x + 0.5) * scale, (y + 0.5) * scale, w * scale, h * scale ), _p! );
}
}