C# 4 and .NET 4

OC40 ❘ ChaPTer 48 GrAphics with Gdi+
}
if (position.X > margin + theLine.Width)
{
return -1;
}
// all is OK. We can return answer
return index;
Finally, on occasion, you also need to convert between line index and page, rather than world, coordinates.
The following methods achieve this:
private Point LineIndexToPageCoordinates(int index)
{
return LineIndexToWorldCoordinates(index) +
new Size(AutoScrollPosition);
}
private int PageCoordinatesToLineIndex(Point position)
{
return WorldCoordinatesToLineIndex(position-new
Size(AutoScrollPosition));
}
Note that when converting to page coordinates, you add the AutoScrollPosition, which is negative.
Although these methods by themselves do not look particularly interesting, they do illustrate a general
technique that you will probably need to use often. With GDI+, you will often find yourself in a situation
where you have been given specific coordinates (for example the coordinates of where the user has clicked
the mouse), and you will need to figure out what item is being displayed at that point. Or it could
happen the other way around — where should a particular display item be displayed Hence, if you are
writing a GDI+ application, you will probably find it useful to write methods that do the equivalent of the
coordinate transformation methods illustrated here.
responding to user input
So far, with the exception of the File menu in the CapsEditor sample, everything you have done in this
chapter has been one way: the application has talked to the user by displaying information on the screen.
Almost all software of course works both ways: the user can talk to the software as well. You are now going
to add that functionality to CapsEditor.
Getting a GDI+ application to respond to user input is actually a lot simpler than writing the code to draw
to the screen. (Chapter 39 covers how to handle user input.) Essentially, you override methods from the
Form class that are called from the relevant event handler, in much the same way that OnPaint() is called
when a Paint event is raised.
The following table lists the methods you might want to override when the user clicks or moves the mouse.
meThod
OnClick(EventArgs e)
OnDoubleClick(EventArgs e)
OnMouseDown(MouseEventArgs e)
OnMouseHover(MouseEventArgs e)
OnMouseMove(MouseEventArgs e)
OnMouseUp(MouseEventArgs e)
Called When …
Mouse is clicked.
Mouse is double-clicked.
Left mouse button is pressed.
Mouse stays still somewhere after moving.
Mouse is moved.
Left mouse button is released.
If you want to detect when the user types in any text, then you will probably want to override the methods
listed in the following table.
www.it-ebooks.info