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| Title | Draw ellipses by specifying their bounding boxes |
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| Keywords | ellipse, bound, box, bounding box |
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| Categories | Graphics |
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Drawing ellipses with the Circle method is a bit counterintuitive. You need to specify the center of the ellipse, the longer of its two radii, and its aspect ratio (ratio of height to width).
Subroutine DrawEllipse lets you specify an ellipse by giving its bounding box. It calculates the center of the ellipse, the radius it needs to specify, and the aspect ratio needed to place the ellipse inside the bounding box.
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' Draw an ellipse in the indicated rectangle.
Private Sub DrawEllipse(ByVal obj As Object, ByVal xmin As _
Single, ByVal ymin As Single, ByVal xmax As Single, _
ByVal ymax As Single)
Dim dx As Single
Dim dy As Single
Dim r As Single
dx = xmax - xmin
dy = ymax - ymin
If dx > dy Then
r = dx / 2
Else
r = dy / 2
End If
obj.Circle ((xmin + xmax) / 2, (ymin + ymax) / 2), r, , _
, , dy / dx
End Sub
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