如何编图形软件开发程序，画图过程的显示，图像分层显示
图层软件架构：
大型图形软件通用的架构，是用一个抽象类（CLayer）的多态派生类对不同图层代码分类管理。
（如果将各种图形绘制以及拖放过程在一个类中编写，最后这个类的代码将无比庞大而且难于维护）

a)支持画直线、矩形和椭圆等多种图形的软件，必须将鼠标按下、释放和拖动等事件联合处理；
b)支持绘图过程中的显示；
c)支持鼠标光标掠过某个图层时显示热点跟踪（HotTrack）状态；
d)单击某个图层时显示选中状态；
e)拖动某个选中状态图层的功能（根据鼠标落点和起点的距离进行偏移）；
f)新绘制的图层和已绘制好选中的图层边框和填充颜色管理。(How to make graphical software development procedures, drawing process display, image layered display
Layer software architecture:
The general architecture of large graphics software is to classify and manage different layers of code using a polymorphic class derived from an abstract class (CLayer).
(if the various graphic drawing and drag and drop processes are written in a class, the code for that class will be extremely large and difficult to maintain)
A) software that supports graphics such as straight lines, rectangles, and ellipses. It must combine the mouse, press, release, and drag events together;
B) support display in drawing process;
C) displays the hot spot tracking (HotTrack) state when the mouse cursor is passed over a layer;
D) displays a selected state when clicked on a layer;
E) drag the function of a selected layer (offset by the distance between the mouse and the starting point);
F) the new layer and the selected layer border and fill color management.)