line method
Implementation
void line( double x1, double y1, double x2, double y2, [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!.drawLine( ui.Offset( x1 + 0.5, y1 + 0.5 ), ui.Offset( x2 + 0.5, y2 + 0.5 ), _p! );
} else {
_c!.drawLine( ui.Offset( (x1 + 0.5) * scale, (y1 + 0.5) * scale ), ui.Offset( (x2 + 0.5) * scale, (y2 + 0.5) * scale ), _p! );
}
}