ASP.NET PDF Viewer using C#, VB/NET

Listing 7-2. Creating a pixmap and a painter before setting up a pen and a brush QPixmap pixmap( 200, 100 ); QPainter painter( &pixmap ); painter.setPen( Qt::red ); painter.setBrush( Qt::yellow ); ... Listing 7-2 sets the pen and brush to Qt s standard colors a red pen and a yellow brush in this case. It is possible to create colors from the red, green, and blue components through the constructor of the QColor class. You can use the static methods QColor::fromHsv and QColor::fromCmyk to create a color from hue, saturation, and value; or cyan, magenta, yellow, and black. Qt also supports an alpha channel, controlling the opacity of each pixel. (You ll experiment with this later in the chapter.) If you want to clear the pen and brush setting, you can use the setPen(Qt::noPen) and setBrush(Qt::noBrush) calls. The pen is used to draw the outlines of shapes, while the brush is used to fill them. Hence, you can draw the outlines without a brush and fill the shapes without a pen.

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There are some optional features we can use in an enum declaration. Example 3-23 uses these, and they provide some insight into how enum types work.

enum DirectionOfApproach : int { Approaching = 0, Leaving = 1 }

In this declaration, we have explicitly specified the governing type for the enumeration. This is the type that stores the individual values for an enumeration, and we specify it with a colon and the type name. By default, it uses an int (exactly as we did in our original const-based implementation of this property), so we ve not actually changed anything here; we re just being more explicit. The governing type must be one of the built-in integer types: byte, sbyte, short, ushort, uint, long, or ulong. Example 3-23 also specifies the numbers to use for each named value. As it happens, if you don t provide these numbers, the first member is assigned the value 0, and we count off sequentially after that, so again, this example hasn t changed anything, it s just showing the values explicitly. We could, if we wanted, specify any value for any particular member. Maybe we start from 10 and go up in powers of 2. And we re also free to define duplicates, giving the same value several different names. (That might not be useful, but C# won t stop you.) We normally leave all these explicit specifiers off, and accept the defaults. However, the sidebar on the next page describes a scenario in which you would need to control the numbers.

The painter class enables you to draw most basic shapes that you might need. This section lists the most useful methods along with example output. First let s take a look at a few classes that are often used as arguments to the drawing method. When drawing, you must tell the painter where to draw the shapes. Each point of the screen can be specified using an x and a y value, as shown in Figure 7-1. As you can see, the y-axis goes from the top, where y is 0 and downward to higher values. In the same way, the x-axis grows while going from the left to the right. When talking about a point, you write (x,y). This means that (0,0) is your upper-left corner of the coordinate system.

Bit Fields with [Flags]

You can create a special kind of enum called a [Flags] enum, also known as a bit field. A bit field is just an ordinary numeric value used in a particular way. When you view a bit field value in binary, each bit represents a particular setting. For example, we could define a bit field to represent the toppings on a bowl of ice cream. We might use the least significant bit to indicate whether a chocolate sauce topping is required. And we could use a different bit to indicate whether chocolate sprinkles are required. The thing that makes bit field enum types different from normal ones is that you can use any combination of values. Because each value gets a whole bit of the number to itself, you can choose for that bit to be either 0 or 1 independently of the value of any other bits. You indicate that your enum works this way by annotating it with a [Flags] attribute, and specifying the values of the members to correspond to the relevant bit patterns. (Actually, the [Flags] attribute turns out to be optional the compiler ignores it, and lets you use any enum as though it were a bit field. The .NET Framework only uses the attribute to work out how to convert enumeration values to text. However, it s a useful signpost to tell other developers how your enum is meant to be used.) Typically, you define a name for each bit, and you can also name some common combinations:

[Flags] enum Toppings { None = 0x00, // Special zero value ChocolateSauce = 0x01, ToffeeSauce = 0x02, ChocolateSprinkles = 0x04, Chocoholic = 0x05, // Combined value, sets 2 bits Greedy = 0x07 // Everything! }

The ScriptManager control is in many ways the core of an Atlas-enabled ASP .NET page. In addition to managing the download of the scripts to the client, it also orchestrates how the page updates and refreshes.

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