We often see a semitransparent
date and place name on a photo. You can draw transparent graphics shapes on
images using the same method: Create a graphics shape using semi- or non-opaque
colors, and then draw on the image.
Listing 9.32 draws graphics shapes on an image. First we create an Image object
and call DrawImage to draw an image. Then we create transparent pens and brushes
and call fill and draw methods to draw graphics shapes. You can add the code in
Listing 9.32 to any menu item or button click event handler.
LISTING 9.32: Drawing semitransparent graphics shapes on an image
Imports
System.Collections.Generic
Imports
System.ComponentModel
Imports
System.Data
Imports
System.Drawing
Imports
System.Linq
Imports
System.Text
Imports
System.Windows.Forms
Public Class Form1
Private Sub Form1_Paint(ByVal
sender As System.Object, ByVal e As
System.Windows.Forms.PaintEventArgs) Handles MyBase.Paint
Dim g As Graphics = Me.CreateGraphics()
g.Clear(Me.BackColor)
' Draw an
image
g.DrawImage(curImage, 0, 0, curImage.Width,
curImage.Height)
' Create pens
and a rectangle
Dim
rect As New
Rectangle(220, 30, 100, 50)
Dim
opqPen As New
Pen(Color.FromArgb(128, 255, 255, 255), 10)
Dim
transpen As New
Pen(Color.FromArgb(128, 255, 255, 255), 10)
Dim
totTransPen As New
Pen(Color.FromArgb(40, 0, 255, 0), 10)
' Draw lines,
rectangle, ellipse, and string using
g.DrawLine(opqPen, 10, 10, 200, 10)
g.DrawLine(transpen, 10, 30, 200, 30)
g.DrawLine(totTransPen, 10, 50, 200,
50)
g.FillRectangle(New SolidBrush(Color.FromArgb(140, 0, 0, 255)), rect)
rect.Y += 60
g.FillEllipse(New
SolidBrush(Color.FromArgb(150, 255, 255, 255)), rect)
Dim
semiTransBrush As New
SolidBrush(Color.FromArgb(90, 255, 255, 50))
g.DrawString("Some
Photo " & vbLf & "Date:
04/09/2001", New Font("Verdana", 14), semiTransBrush, New RectangleF(20, 100, 300, 100))
' Dispose of
object
g.Dispose()
End Sub
End Class
Figure 9.43 shows the output from Listing 9.32. Lines, text, a rectangle, and an
ellipse are drawn on top of the image, but you can see through them because
these shapes are semitransparent.
FIGURE 9.43: Drawing semitransparent shapes on an image
Conclusion
Hope the article would have helped you in understanding Alpha Blending and
Images in GDI+. Read other articles on GDI+ on the website.