Repaint Your Forms With Style
The little-known SetStyle method lets you control the way a form redraws.
by Ken Getz
VSLive! Orlando, September 17, 2002
Note: Ken Getz presented the full-day workshop, "Build a Rich Client App with Visual Studio .NET," with Brian Randell at VSLive! Orlando. This tip is from that workshop's material.
It's easy to create a gradient that fills a region, using GDI+ and Windows Forms. You can create linear gradients or path gradients, using simple methods provided by the .NET Framework. The real problem, however, is that these complex background graphics are resource-intensive. Recently, I was working on an analog clock demonstration, using a gradient as the fill for the clock face. Every second, as the clock repainted its face to display the correct positioning for the clock hands, it also repainted the entire background gradient. Even on a fast machine, it wasn't pretty. I'll introduce you to the SetStyle method, which lets you specify how and when your form redraws.
To get started, try this code out for some psychedelic, tie-dyed fun. Modify a new form's Paint event so that it contains this code:
Private Sub frmMain_Paint( _
ByVal sender As Object, _
ByVal e As PaintEventArgs) _
Handles MyBase.Paint
Dim path As New GraphicsPath()
Dim pt As New PointF()
Dim rct As Rectangle = Me.ClientRectangle
path.AddRectangle(rct)
Dim pgb As New PathGradientBrush(path)
pt = New PointF( _
CType(Me.ClientSize.Width / 2, Single), _
CType(Me.ClientSize.Height / 2, Single))
pgb.CenterPoint = pt
Dim Colors() As Color = _
{Color.Red, Color.Orange, Color.Yellow, _
Color.Green, _
Color.Blue, Color.Indigo, Color.Violet}
Dim Positions() As Single = _
{0.0, 0.1, 0.2, 0.4, 0.6, 0.8, 1}
Dim cb As ColorBlend = New ColorBlend()
cb.Colors = Colors
cb.Positions = Positions
pgb.InterpolationColors = cb
e.Graphics.FillRectangle(pgb, rct)
Dim f As New StringFormat()
f.Alignment = StringAlignment.Center
e.Graphics.DrawString( _
Date.Now.ToLongTimeString, _
New Font("Tahoma", 13), Brushes.White, pt, f)
End Sub
There's a lot of code here, but it's pretty simple stuff. The code creates a new GraphicsPath object, adds a rectangle filling the whole form to the GraphicsPath, and then creates a GradientBrush object based on the GraphicsPath. The code sets up the center point for the gradient, creates an array of colors for the gradient to use, creates the array of positions (fractions of the entire radius of the gradient at which the colors change), creates a new default ColorBlend object, sets properties of the gradient, and fills the rectangle with the gradient.
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