Introduction
In VC++ we have a class CRectTracker which helps drawing the
trackers and also there is function a DrawFocusRect() with which
tracker behavior can be achieved. In C# I did not find any kind of such
functionality (if there is then I am unaware at the moment.). So I decided to
make program which draw box with tracker and allows manipulation with the box
with the help of trackers.
Key features
- Drawing trackers
- Moving the boxes having trackers attached to it.
- Resizing the box with the help of trackers.
- Selection is made in Z Order.
I tried to avoid Form�s Invalidate() function as it generates
flickering effects and drawing is not smooth. I designed the program in a way to
maximize the usage of double buffering to avoid flickering effect.
Using the code
Class CRectTracker
| Methods |
Functionality |
DrawSelectionGhostRect() |
Draws the given ghost rectangle on the specified bitmap |
InitTrackerRects() |
Initializes the eight rectangle of the tracker. |
DrawSelectionTrackers() |
Draws the already initialized tracker rectangles |
CursorCheck() |
Checks the position of the cursor and changes the form cursor with
appropriate cursor and returns the border of the rectangle for the resizing
purpose. |
In the main program there are three modes of the program. First is the �None
mode� which indicates that user is not drawing, second mode is the �Drawing
mode� and it is invoked when user selects the Box icon from the toolbar and
third is the �selection mode� it is invoked when user selects a box for changing
the positioning or size.
There is main bitmap which holds the current drawing. Whenever a change is
required like drawing rubber band selection or drawing tracker a copy of the
main bitmap is made and saved in TrackerImage bitmap and all the changes are
made in it and in the end it is assigned to the main bitmap. Even when repaint
is required then RePaintForm() function is called instead of
calling paint() function of the form to avoid the flickering
effect.
Conclusion
A simple program that demonstrates double buffering & tracker drawing is
included. OnPaint() generates flickering effects so it is
recommended to draw first on the bitmap and then on the form.
