Draw a circle that follows the mouse cursor without latent circles

Posted on 2009-03-31
Medium Priority
Last Modified: 2013-12-17
I have a form and would like to have a circle follow the mouse cursor.  Similarly to what is shown in Adobe Photoshop when you are in line brush mode and you can see the size of the brush you are about to draw.  My problem occurs when I place a background image on the form.

To use the example code below.  Create form and paste the code into the form (the size of my form is 804X584).  Run the application.  Initially you will have great performance.  However if you give the form a background image.  In my situation I just used C:\Documents and Settings\All Users\Documents\My Pictures\Sample Pictures\Blue hills.jpg and you will see some latent circles when you move the mouse very fast.  The attached picture shows you the latent circles.

I've tried using the OvalShape from Microsoft.VisualBasic.PowerPacks but the performance of that was even worse.

Some notes about the code below:
1.  I pretty draw the circle in the function ShowQualityCircle (called from MouseMove).  Here I call Invalidate without any arguments.  When I tried it with a rectangle I got a number of latent circles.  I even tried a larger rectangles but when I moved the mouse very fast I still got latent circles.
2.  Without the call to draw the circle in the Paint routine I got a number of latent rectangles, so that was necessary.

You help would be greatly appreciated.

Public Class Form1
  Private QCircle As New Rectangle(0, 0, 0, 0)
  Private Sub Form1_MouseMove(ByVal sender As Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles Me.MouseMove
    ShowQualityCircle((e.X), (e.Y), 20)
  End Sub
  Private Sub Form1_Paint(ByVal sender As Object, ByVal e As System.Windows.Forms.PaintEventArgs) Handles Me.Paint
    If QCircle.Width > 0 AndAlso QCircle.Height > 0 Then
      DrawCircle(e.Graphics, Color.Red, QCircle.X, QCircle.Y, QCircle.Width, QCircle.Height, 0, 360)
    End If
  End Sub
  Private Sub DrawCircle(ByRef g As Graphics, ByVal currentColor As Color, ByVal x As Single, ByVal y As Single, ByVal width As Single, ByVal height As Single, ByVal startAngle As Single, ByVal sweepAngle As Single)
    Dim myBrush As New SolidBrush(currentColor)
    Dim myPen As New Pen(myBrush)
    myPen.Width = 1
    g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias
    g.DrawArc(myPen, x, y, width, height, startAngle, sweepAngle)
  End Sub
  Private Sub ShowQualityCircle(ByVal imgX As Integer, ByVal imgY As Integer, ByVal mypenradius As Integer)
    QCircle = New Rectangle(imgX - mypenradius, imgY - mypenradius, mypenradius * 2, mypenradius * 2)
    Dim g As Graphics = Me.CreateGraphics()
    DrawCircle(g, Color.Red, QCircle.X, QCircle.Y, QCircle.Width, QCircle.Height, 0, 360)
  End Sub
End Class

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Question by:tedunni
  • 3
LVL 86

Accepted Solution

Mike Tomlinson earned 1000 total points
ID: 24033304
Create a CURSOR instead of trying to draw that puppy all over the place...  ;)
Public Class Form1
    Private radius As Integer = 20
    Private startAngle As Integer = 0
    Private sweepAngle As Integer = 360
    Private currentColor As Color = Color.Red
    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    End Sub
    Private Sub CreateCursor()
        Dim bmp As New Bitmap(radius * 2, radius * 2)
        Dim g As Graphics = Graphics.FromImage(bmp)
        Dim myPen As New Pen(currentColor, 1)
        g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias
        g.DrawArc(myPen, 0, 0, bmp.Width - 1, bmp.Height - 1, startAngle, sweepAngle)
        Dim C As New Cursor(bmp.GetHicon)
        Me.Cursor = C
    End Sub
End Class

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Author Closing Comment

ID: 31564963
Thanks, this solution is perfect.

Author Comment

ID: 24051593
Idle_Mind, I'm going to ask a related question regarding this, but if I were to have a radius of say 48 it only draws part of the circle.  Additionally, if the radius gets quite large (try 576), then I get a GDI+ exception.  Any suggestions.  

Btw, the related question wizard keeps asking me to assign a title for the question (Even when I assign one), and so I'm posting here but once I get that figured out I'll post the link to the related question.

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