plus控件实现手写签名板

import win.ui;
/*DSG{{*/
var winform = win.form(text="aardio form";right=904;bottom=602)
winform.add(
button={cls="button";text="清空";left=289;top=489;right=571;bottom=558;z=1};
button2={cls="button";text="保存";left=598;top=490;right=808;bottom=558;z=3};
plus={cls="plus";left=66;top=49;right=821;bottom=447;bgcolor=16777215;notify=1;z=2};
plus2={cls="plus";left=71;top=473;right=254;bottom=577;foreRepeat="scale";z=4}
)
/*}}*/

import gdip;
import gdip.bitmap
import gdip.snap;
 
//图形对象graphics(可以看作是画板)
var graphics = gdip.graphics( winform.plus )
//加上抗锯齿功能
graphics.smoothingMode = 4/*_GdipSmoothingModeAntiAlias*/ ; 

var penColor = 0xFF000000;//线颜色
var penWidth = 8;//线宽
var startcap = 2;//起点线帽,指定线帽后画笔宽度为线帽宽度
var endcap = 2;//终端线帽,指定线帽后画笔宽度为线帽宽度
var drawData; //点坐标数组
var undoArr = {};//存放每一次鼠标弹起后的点坐标信息

winform.button.oncommand = function(id,event){
	//winform.redraw()
	graphics.clear(0xFFFFFFFF) ;//清空画板，并填充指定颜色
	undoArr = {};
}

//定义鼠标初始坐标
var x1 = 0
var y1 = 0

winform.plus.onMouseDown = function(wParam,lParam){
    x1,y1 = win.getMessagePos(lParam);
    drawData = {::POINTF(x1,y1)}
}

winform.plus.onMouseMove = function(wParam,lParam){
	if( wParam & 0x1/*_MK_LBUTTON*/ ){
		var x2,y2 = win.getMessagePos(lParam);
		
		table.push(drawData,::POINTF(x2,y2) )
		var pen = gdip.pen( penColor, penWidth,2/*_GdipUnitPixel*/);
		pen.startCap = startcap 
		pen.endCap = endcap
		
		graphics.drawLine( pen, x1, y1, x2, y2)
		x1 = x2;
		y1 = y2;
		
		pen.delete()
	}
}

winform.plus.onMouseUp = function(wParam,lParam){
    //var x,y = win.getMessagePos(lParam);
	table.push(undoArr,drawData);
	drawData = null;
}


//winform.plus.modifyStyle(, 0x2000000/*_WS_CLIPCHILDREN*/)
//winform.modifyStyle(, 0x2000000/*_WS_CLIPCHILDREN*/ )

winform.button2.oncommand = function(id,event){
	var bitmap = gdip.snap(winform.plus.hwnd)
	var old = winform.plus2.setForeground(bitmap,,true) //显示到plus2上
	if( old ) old.dispose();
	bitmap.save("c:\截图.jpg",80) //保存位图
}

//重绘
winform.plus.onDrawForegroundEnd = function(graphics,rc){
    var pen = gdip.pen( penColor, penWidth,2/*_GdipUnitPixel*/);
	pen.startCap = startcap 
	pen.endCap = endcap
	
	if(#undoArr>0){
		for(i=1;#undoArr;1){
			for(j=2;#undoArr[i];1){
				graphics.drawLine(pen,undoArr[i][j-1].x,undoArr[i][j-1].y,undoArr[i][j].x,undoArr[i][j].y); 	
			}
		}
	}
	pen.delete()
}

winform.show();
win.loopMessage();

实现了在plus上签名并保存成位图，但有个问题，当窗体尺寸调整或最小化恢复后，plus上的graphics会丢失，这个怎么解决？？

↑↑↑↑↑ 上面的问题，参考官方的画板解决了