ID Number: Q83906
1.00
WINDOWS
Summary:
This article describes how to use the Circle statement to draw an ellipse
of a specified width and height by calculating the radius and aspect
ratio appropriate for the dimensions of the ellipse and the units of
measurement, determined by the ScaleMode property.
This information applies to Microsoft Visual Basic programming system
version 1.0 for Windows.
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 on the form.
The program draws an ellipse centered in the form, and touching the
sides of the form. Resize the form and/or click on the form again to
repeat the demonstration.
Additional reference words: 1.00