用VC++开发的一个画笔，通过拖动鼠标左键可以实现绘画，但画笔颜色更改不了，画笔不能出现，还请高手指点。-VC++ development with a brush, can be achieved by dragging the left mouse button painting, but can not change the pen color, pen can not appear, please also master pointers.