Problem: Need to take a visual basic ellipse (whose code can not be

changed) and draw the exact ellipse in cppbuilder.

Need a function to translate a visual basic ellipse drawn with the circle

command (that takes an aspect ratio, a radius, and a center set of points)

and translate it to the winapi ellipse/vcl ellipse that takes 2 sets of

points for each edge of a rectange in which the ellipse is bound. For the

visual basic side of things, the radius was calculated by using

centerX = (X + startx) / 2

centerY = (Y + starty) / 2

Radius = ((Abs(X - centerX) ^ 2 + Abs(Y - centerY) ^ 2) ^ 0.5)

and the aspect was calculated by using

CircleAspect = Abs((Y * ScaleRatio - starty * ScaleRatio) / (X - startx))

startx and starty are where the mouse was originally clicked, and x,y is

where the mouseup condition occurs in vb.

Everything has to look the same and be proportional.

This seems like it should be a simple geometry problem. The following on

the visual basic circle command should be of help:

How to Draw an Ellipse with Circle Statement in VB

The information in this article applies to:

- Standard and Professional Editions of Microsoft Visual Basic for

Windows, versions 2.0 and 3.0

- Microsoft Visual Basic programming system for Windows, version 1.0

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.

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.

Additional reference words: 1.00 2.00 3.00 KBCategory: kbgraphic kbprg

kbcode KBSubcategory:

Thanx,

Davinci