C# 4 and .NET 4

OC10 ❘ ChaPTer 48 GrAphics with Gdi+
ab.X = (int)abFloat.X;
ab.Y = (int)abFloat.Y;
Point ab1 = Point.Round(abFloat);
Point ab2 = Point.Truncate(abFloat);
Point ab3 = Point.Ceiling(abFloat);
// but conversion back to PointF is implicit
PointF abFloat2 = ab;
You might be wondering what a unit is measured in. By default, GDI+ interprets units as pixels along the
screen (or printer, whatever the graphics device is). This is how the Graphics object methods view any
coordinates that they are passed as parameters. For example, the point new Point(20,10) represents
20 pixels across the screen and 10 pixels down. Usually these pixels are measured from the top-left corner
of the client area of the window, as has been the case in the previous examples. However, that will not
always be the case. For example, on some occasions you might want to draw relative to the top-left corner
of the whole window (including its border), or even to the top-left corner of the screen. In most cases,
however, unless the documentation tells you otherwise, you can assume that you are talking about pixels
relative to the top-left corner of the client area.
You learn more on this subject later in this chapter, after scrolling is examined, when we discuss the three
different coordinate systems in use — world, page, and device coordinates.
Fize and sizef
As with Point and PointF, sizes come in two varieties. The Size struct is for int types. SizeF is available
if you need to use float types. Otherwise, Size and SizeF are identical. This section focuses on the Size
struct.
In many ways, the Size struct is identical to the Point struct. It has two integer properties that represent
a distance horizontally and vertically. The main difference is that instead of X and Y, these properties are
named Width and Height. You can represent the earlier diagram using this code:
Size ab = new Size(20,10);
Console.WriteLine("Moved {0} across, {1} down", ab.Width, ab.Height);
Although Size mathematically represents exactly the same thing as Point, conceptually, it is intended to
be used in a slightly different way. Point is used when you are talking about where something is, and Size
is used when you are talking about how big it is. However, because Size and Point are so closely related,
there are even supported conversions between these two:
Point point = new Point(20, 10);
Size size = (Size) point;
Point anotherPoint = (Point) size;
As an example, think about the rectangle you drew earlier, with top-left coordinate (0,0) and size (50,50).
The size of this rectangle is (50,50) and might be represented by a Size instance. The bottom-right corner is
also at (50,50), but would be represented by a Point instance. To see the difference, suppose that you draw
the rectangle in a different location, so that its top-left coordinate is at (10,10):
dc.DrawRectangle(bluePen, 10,10,50,50);
Now the bottom-right corner is at coordinate (60,60), but the size is unchanged at (50,50).
The addition operator has been overloaded for Point and Size structs so that it is possible to add a Size to
a Point struct, resulting in another Point struct:
static void Main(string[] args)
{
Point topLeft = new Point(10,10);
Size rectangleSize = new Size(50,50);
Point bottomRight = topLeft + rectangleSize;
Console.WriteLine("topLeft = " + topLeft);
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