Display circles with random colors. in Visual Studio .NET

Creation QR Code JIS X 0510 in Visual Studio .NET Display circles with random colors.

Dim r As New Random()

Part IV:

For y As Integer = 10 To 400 Step 40 Dim br As New SolidBrush( _ Color.FromArgb(r.Next(0, 255), r.Next(0, 255), r.Next(0, 255))) gr.FillEllipse(br, x, y, 30, 30) br.Dispose() Next Next Dispose the region, if you are done with it. reg.Dispose()

The Graphics object exposes the VisibleClipBounds property, which returns a Rectan gleF object that represents the visible area of the corresponding window. You can use this property to optimize your graphic routines by not processing shapes that are com pletely outside this rectangular area. When used with the printer, this property returns the printable area of the page.

One of the great features of GDI+ is alpha blending, which is the ability to define semitransparent colors and then use them to draw or paint all kinds of shapes. You define the transparency degree in the first argument of the Color.FromArgb method, passing a number in the range of 255 (opaque) to 0 (completely transparent). Any value less than 255 causes the background to show behind the figure being drawn. For example, the result visible in Figure 17-12 was produced by the following code:

gr.FillRectangle(Brushes.Green, 20, 20, 200, 200)

Dim br1 As New SolidBrush(Color.FromArgb(128, 255, 0, 0))

gr.FillEllipse(br1, 120, 50, 200, 120)

17:

Dim br2 As New SolidBrush(Color.FromArgb(30, 0, 0, 255))

gr.FillRectangle(br2, 160, 80, 120, 200)

Dim p As New Pen(Color.FromArgb(128, 128, 128, 128), 5)

gr.DrawEllipse(p, 100, 100, 200, 200)

br1.Dispose()

br2.Dispose()

p.Dispose()

Figure 17-12

All the code samples seen so far assumed that the coordinate origin was the upper left corner of the client area and that all values were in pixels. However, the Graphics object is highly flexible and lets you change these default settings as your needs dic tate. To take advantage of this ability, you should understand that three different coor dinate systems come into play whenever you draw any graphic object (including bitmaps and text):

The world coordinate system This is the system that you use to model your graphic world. All the coordinates that you pass to graphic methods are expressed in this system. The page coordinate system This is the system used by the surface on which you re drawing, be it a form, a control, or a printer document. By default, the ori gin and scale of this system coincide with the world coordinate system, but they don t have to. For example, you can have the origin of the world system at the center of the form, which might be convenient if you re plotting a mathematical function. The conversion between world and page coordinates is called world transformation.

Part IV:

The device coordinate system This is the system used by the physical device on which the drawing operation occurs that is, the actual window if you re drawing on the screen or the sheet of paper if you re sending output to the printer. You can define precisely the unit of measure of the system (inches, millimeters, and so on), the ratio between the horizontal and vertical axes, and more. The conversion between page and device coordinates is called page transformation. Notice that you can t perform translations along the X or Y axis, nor can you reverse the direction along these axes. In other words, you can t flip an image using page transformation.

The Graphics object exposes several methods for affecting how world transformation is performed. The TranslateTransform method lets you change the origin of the coor dinate system; so, for example, you can draw the same GraphicsPath object in a differ ent location simply by translating the origin of the X-Y axes: