C# 4 and .NET 4

editing a Text Document: The Capseditor example ❘ OC39
the required coordinates of the top-left corner of the item. The returned coordinates are world coordinates,
but that is fine because you have already called TranslateTransform() on the Graphics object so that you
need to pass it as a world coordinate, rather than a page, when asking it to display items.
Coordinate Transforms
This section examines the implementation of the helper methods that are written in the CapsEditor
sample to help you with coordinate transforms. These are the WorldYCoordinateToLineIndex() and
LineIndexToWorldCoordinates() methods referred to in the previous section, as well as a couple of other
methods.
First, LineIndexToWorldCoordinates() takes a given line index, and works out the world coordinates of
the top-left corner of that line, using the known margin and line height:
private Point LineIndexToWorldCoordinates(int index)
{
Point TopLeftCorner = new Point(
(int)margin, (int)(lineHeight*index + margin));
return TopLeftCorner;
}
code download CapsEditor.sln
You also use a method that roughly does the reverse transform in OnPaint().
WorldYCoordinateToLineIndex() works out the line index, but it takes into account only a vertical world
coordinate because it is used to work out the line index corresponding to the top and bottom of the clip
region:
private int WorldYCoordinateToLineIndex(int y)
{
if (y < margin)
{
return -1;
}
return (int)((y-margin)/lineHeight);
}
There are three more methods, which will be called from the handler routine that responds to the user
double-clicking the mouse. First, you have a method that works out the index of the line being displayed at
given world coordinates. Unlike WorldYCoordinateToLineIndex(), this method takes into account the x
and y positions of the coordinates. It returns -1 if there is no line of text covering the coordinates passed in:
private int WorldCoordinatesToLineIndex(Point position)
{
if (!documentHasData)
{
return -1;
}
if (position.Y < margin || position.X < margin)
{
return -1;
}
int index = (int)(position.Y-margin)/(int)this.lineHeight;
// check position is not below document
if (index >= documentLines.Count)
{
return -1;
}
// now check that horizontal position is within this line
TextLineInformation theLine =
(TextLineInformation)documentLines[index];
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