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Dragging graphics with mouse

Posted on 2003-11-19
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Last Modified: 2013-11-20
I've created a scrollview in which graphic boxes, lines, charts,  etc. are drawn on the screen. I've been drawing them by overriding the OnDraw of the view and passing the pDC to various object classes I've created to draw the objects.

Now I'm trying to add some functionality by allowing the user to click and drag the objects. I'm thinking that redrawing every time the mouse moves (using the windows message) will cause major flicker and is a bad idea. I need the objects (and a mouse popup) to follow the cursor.

My question is, what would be the best technique to allow users to drag drawn objects? Should I just invalidate a portion of the window and re-draw?

(note: point value higher since I need the solution quickly. probably not very difficult)
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Question by:JoyBurke
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Expert Comment

by:AlexFM
ID: 9780158
Check out MFC sample DRAWCLI. It shows how to do this and redraws the screen by optimal way using memory DC and minimizing the clipping area. It has all you need to drag graphic objects except automatic scrolling during dragging. I will try also to find the sample which shows automatic scrolling.
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Expert Comment

by:AlexFM
ID: 9780314
About automatic scrolling:

http://www.microsoft.com/msj/0898/wicked0898.aspx

This sample implements automatic scrolling by timer in tree control, but you can get an idea how to do this in scroll view.
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Author Comment

by:JoyBurke
ID: 9780318
That example uses OleDataObjects. Do I need to learn to use OleObjects to do this?

Previously I had CObjects stored in a list. They are created only for the view and don't need to be saved or have extensive capability.

The example is helpful, but I'm having a hard time picking through it to find what I need to use.
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AlexFM earned 200 total points
ID: 9780346
And the last point:

DRAWCLI makes full redrawing of dragged object. Another approach is drawing only hatched rectangle during dradding and redraw the full object only when mouse button is released. To do this check out MFC class CRectTracker and MFC sample TRACKER.
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Expert Comment

by:AlexFM
ID: 9780357
No, ignore all OLE stuff and read only about simple graphic objects like rectangles.
If you need a fast solution, use CRectTracker.
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Author Comment

by:JoyBurke
ID: 9780529
I'm a beginner and having a hard time picking through all these examples.

what is a hatched rectangle and how does it get drawn?
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Author Comment

by:JoyBurke
ID: 9780601
Could you give me a basic pseudocode? (ie: On mouse move, redraw just the rectangle by....)
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LVL 48

Expert Comment

by:AlexFM
ID: 9780607
This is a thin dotted rectangle which is moved with the mouse showing current position of the object. When user releases mouse, object itself is redrawn on the new place. Build the TRACKER sample and see how it works. CRectTracker class handles all implementation details. This is really fast solution.
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Author Comment

by:JoyBurke
ID: 9781606
Thanks for all your help and patience!
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