HTML clipboardAs we discussed in the previous section, from
the programming perspective, drawing on the Web is the same as drawing in
Windows Forms, except for a few small differences. Drawing on the Web is often
called "drawing on the fly" (or "graphics on the fly"). The code in Listing 12.4
draws various graphics objects, including lines, text, rectangles, and an
ellipse. We create various pens, brushes, and a 300X300 bitmap. Then we create a
Graphics object from this bitmap by calling Graphics.FromImage. Once we have a
Graphics object, we can call its methods to draw and fill graphics shapes.
After creating the Graphics object, we set its smoothing mode to AntiAlias,
create font and size objects, and call the DrawString, DrawLine and DrawEllipse
methods to draw text, lines, and ellipse, respectively. At this point the bitmap
we created contains these objects. The next step is to call the Save method and
send the image to the browser, which we do with the Bitmap.Save method. Finally,
we call the Dispose method to dispose of various objects.
LISTING 12.4: Drawing graphics objects on the fly
'Contruct brush and pens
Dim redPen
As New
Pen(Color.Red, 3)
Dim brush As
New HatchBrush(HatchStyle.Cross, Color.Yellow,
Color.Green)
Dim hatchPen As
New Pen(brush, 2)
Dim bluePen As
New Pen(Color.Blue, 3)
Dim curBitmap
As New Bitmap(300, 200)
Dim g As
Graphics = Graphics.FromImage(curBitmap)
g.SmoothingMode = SmoothingMode.AntiAlias
Dim testString
As String =
"Hello GDI+ On the Web"
Dim verdana14
As New Font("Verdana",
14)
Dim Tahoma18__1
As New Font("Tahoma",
18)
Dim nChars As
Integer
Dim nLines
As Integer
'Call MeasureString to measure a string
Dim sz
As SizeF = g.MeasureString(testString, verdana14)
Dim testString
As String =
"Hello GDI+ On the Web"
Dim verdana14
As New Font("Verdana",
14)
Dim Tahoma18__1
As New Font("Tahoma",
18)
Dim nChars As
Integer
Dim nLines
As Integer
'Call MeasureString to measure a string
Dim sz
As SizeF = g.MeasureString(testString, verdana14)
Dim stringDetails
As String =
"Height: " & sz.Height.Tostring() &
" , Width: " & sz.Width.Tostring()
g.DrawString(testString, verdana14, Brushes.Wheat,
New PointF(40, 70))
g.Drawrectangle(New Pen(Color.Red, 2), 40.0F, 70.0F, sz.Width, sz.Height)
sz = g.MeasureString("Ellipse",
tahoma18, New SizeF(0.0F, 100.0F),
New StringFormat(), nChars, nLines)
Dim stringDetails
As String =
"Height: " & sz.Height.ToString() &
", Width: " & sz.Width.ToString() &
", Lines: " & nLines.ToString() &
", Chars: " & nChars.ToString()
'Draw lines
g.DrawLine(Pens.WhiteSmoke, 10, 20, 180, 20)
g.DrawLine(Pens.White, 20, 10, 20, 180)
'Fill ellipse
g.FillEllipse(brush, 120, 100, 100, 100)
'Draw string
g.DrawString("Ellipse",
tahoma18, Brushes.Beige, New PointF(40, 20))
'Draw ellipse
g.DrawEllipse(New
Pen(color.Yellow, 3), 40, 20, sz.Width, sz.Height)
'Send output to the browser and dispose of
objects
curBitmap.Save(Me.Response.OutputStream,
ImageFormat.Jpeg)
g.Dispose()
For all practical purposes, Listing 12.4 could be a Windows Forms application.
The only new code required creates a Bitmap object and calls its Save method to
send output to the browser. We use the DrawString method to draw text, the
DrawLine method to draw lines, and the DrawRectangle method to draw
rectangles-just as in any other GDI+ application.
Figure 12.10 shows the output from Listing 12.4. The program draws lines,
ellipses, and text.
FIGURE 12.10: Drawing various graphics objects.