How to Draw an Ellipse with Circle Statement in VB (83906)

MORE INFORMATION

The Circle statement takes two arguments that determine the shape of the ellipse drawn: the radius and the aspect ratio. For example:

   Circle (x, y), radius,,,, aspect
				

The aspect ratio is the y-radius divided by the x-radius of the ellipse drawn. An aspect ratio of 1.0 (the default) yields a perfect (non-elliptical) circle. If the aspect ratio is less than one, the radius argument specifies the x-radius. If the aspect ratio is greater than one, the radius argument specifies the y-radius. Both the x-radius and the y-radius are measured in units of the x-axis.

Steps to Create Example Program

1. Run Visual Basic, or from the File menu, choose New Project (ALT, F, N) if Visual Basic is already running. Form1 is created by default.
2. Enter the following code in the Form1_Click event procedure:

   Sub Form_Click ()
       Cls
   
       ' Set x-axis units different from y-axis to demonstrate
       ' that the ellipse still comes out right.
       Form1.ScaleWidth = Rnd * 100
       Form1.ScaleHeight = Rnd * 100
       Print "ScaleWidth  = "; Format$(Form1.ScaleWidth, "#")
       Print "ScaleHeight = "; Format$(Form1.ScaleHeight, "#")
   
       ' Print the dimensions of the ellipse.
       ' Draw an ellipse centered on the form and touching the
       ' borders.
       w = Form1.ScaleWidth / 2
       h = Form1.ScaleHeight / 2
       Call ellipse(Form1, w, h, w, h)
   End Sub
   						

3. Enter the following code in the general Declarations section:

   ' ellipse(frm, x, y, w, h)
   '   Purpose
   '     Draws an ellipse on a form.
   '   Parameters
   '     frm  -- the form to draw on
   '     x, y -- specify the center of the ellipse.
   '     w, h -- specify the width and height.
   '
   Sub ellipse (frm As Form, ByVal x!, ByVal y!, ByVal w!, ByVal h!)
       Dim swt As Long    ' ScaleWidth  in twips
       Dim sht As Long    ' ScaleHeight in twips
       Dim k As Double    ' conversion factor for x-units to y-units
       Dim ar As Double   ' aspect ratio
       Dim r As Single    ' radius
       Dim save_mode As Integer   ' for saving and restoring ScaleMode
       Dim save_width As Single   ' for saving and restoring ScaleWidth
       Dim save_height As Single  ' for saving and restoring ScaleHeight
   
       ' Check arguments.
       If w <= 0 Or h <= 0 Then Stop
   
       ' Determine form dimensions in twips.
       save_mode = frm.ScaleMode  ' save Scale... properties
       save_width = frm.ScaleWidth
       save_height = frm.ScaleHeight
       frm.ScaleMode = 1          ' set units to twips
       swt = frm.ScaleWidth
       sht = frm.ScaleHeight
       frm.ScaleMode = save_mode  ' restore Scale... properties
       If frm.ScaleMode = 0 Then
           frm.ScaleWidth = save_width
           frm.ScaleHeight = save_height
       End If
   
   ' Compute conversion factor of x-axis units to y-axis units.
       k = frm.ScaleWidth / frm.ScaleHeight * sht / swt
   
   ' Compute aspect ratio and radius.
       ar = k * h / w
       If ar <= 1 Then
           r = w
       Else
           r = k * h
       End If
   
       ' Draw the ellipse.
       frm.Circle (x, y), r, , , , ar
   End Sub
   						

4. Press F5 to run the program. Then click the form.

The program draws an ellipse centered in the form, and touching the sides of the form. Resize the form and/or click the form again to repeat the demonstration.