To help you put it all together, the entire program source follows. To use this code, you need to name your form BlendForm and add an HScrollBar component and name it BlendScroll. You will also need two image files.
Imports System.Drawing.Drawing2D
Public Class BlendForm
Private PositionArray(2) As Single
Private FactorArray(2) As Single
Private i1 As Image = _
Image.FromFile("C:\image1.gif")
Private i2 As Image = _
Image.FromFile("C:\image2.gif")
Private i As Image = i1
Private StartRecX As Integer = _
CInt((Me.Width - i.Width) / 2)
Private StartRecY As Integer = _
CInt(((Me.Height - i.Height) / 2) - 20)
Protected Overrides Sub OnPaint( _
ByVal e As System.Windows.Forms.PaintEventArgs)
Dim g As Graphics = e.Graphics
Using myBrush As LinearGradientBrush _
= New LinearGradientBrush( _
Me.ClientRectangle, _
Color.Blue, Color.Red, _
LinearGradientMode.Horizontal)
Dim myBlend As Blend = New Blend(2)
myBlend.Factors = FactorArray
myBlend.Positions = PositionArray
myBrush.Blend = myBlend
g.FillRectangle( _
myBrush, Me.ClientRectangle)
g.DrawImage( _
i, StartRecX, StartRecY, i.Width, i.Height)
MyBase.OnPaint(e)
End Using
End Sub
Private Sub BlendScroll_Scroll( _
ByVal sender As System.Object, _
ByVal e As System.Windows.Forms.ScrollEventArgs) _
Handles BlendScroll.Scroll
PositionArray(1) = BlendScroll.Value / 91
' adjustment to compensate for bug in scroll control
' see http://visualbasic.about.com/b/a/256812.htm for details
If PositionArray(1) < 0.5 Then
i = i1
Else
i = i2
End If
Me.Invalidate()
End Sub
Private Sub BlendForm_Load( _
ByVal sender As System.Object, _
ByVal e As System.EventArgs) _
Handles MyBase.Load
FactorArray = New Single() {0.0, 0.5, 1.0}
PositionArray = New Single() {0.0, 0.5, 1.0}
SetStyle(ControlStyles.AllPaintingInWmPaint Or _
ControlStyles.OptimizedDoubleBuffer Or _
ControlStyles.UserPaint, True)
End Sub
End Class
Part 5 of the tutorial explains the concept of a graphics coordinate space. A coordinate space is a key element for understanding graphic transformations using the Matrix object that is also featured in Part 5.
