How to drag a polygon in MFC?

Question

I'm new to MFC. I know how to draw a line and how to scribble in MFC. I use CDC and some functions such as LineTo() and MoveTo() to do this. Moreover, I've got FillRect() and Rectangle().Now I want to drag my rectangle or any polygon in the view.It's like you drag a icon on your desktop.

I think the first step is to get the region.Then erase the old polygon and when the mouse move draw a same polygon which depends on the point where the mouse go. So I search region in MSDN and I got Region class and CRgn class.But before I look into these two class I want to know whether I'm in the right direction.

I need more suggestions on how to learn MFC. Actually,all I need is to finish my homework which is mainly about draw polygons and drag them and link them by line. And I hope I can finish this homework all by myself and MSDN. Can MSDN help me do that?

You don't need regions to do this - store your polygon points somewhere in your program when the polygon is first drawn, then handle mouse-down, mouse-up and mouse-move to find the offset you need to draw in a new position. Add the offset to the original points during drawing .... you get the idea? — Roger Rowland

ScottMcP-MVP ScottMcP-MVP · Accepted Answer · 2013-11-27T15:00:48

The CDC::Polyline function will draw a polygon much faster than using LineTo and MoveTo.

You do not need region and do not need to erase the old polygon. Instead, you need to draw everything in the view OnDraw. Any change you want to make with the mouse should change the array of coordinates that represent the polygon and then call Invalidate. In other words, do not draw in the mouse message handlers. Calling Invalidate in the mouse message handlers will cause OnDraw to be called later and it should repaint the entire view.

How to drag a polygon in MFC?

1 Answers