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Drawing Arrows

SimonWilliams
on
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Last Modified: 2012-06-22
I would like to know if there are any routines that, given
a line (x1,y1)-(x2,y2), will automatically draw an arrow-
head on it pointing in the right direction.
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Commented:
There's no built in function for drawing arrows, but the following function will do it.

Private Function Arrow(x1 As Long, y1 As Long, x2 As Long, y2 As Long, Direction As Long) As Long
Dim xdiff As Long

xdiff = x2 - x1
xdiff = xdiff / 5

Form1.Line (x1, y1)-(x2, y2)
If Direction = 1 Then
    x1 = x2 - xdiff
    y1 = y2 - xdiff
    Form1.Line (x2, y2)-(x1, y1)
    y1 = y1 + (xdiff * 2)
    Form1.Line (x2, y2)-(x1, y1)
Else
    x2 = x1 + xdiff
    y2 = y1 - xdiff
    Form1.Line (x1, y1)-(x2, y2)
    y2 = y2 + (xdiff * 2)
    Form1.Line (x1, y1)-(x2, y2)
End If

End Function

Just pass it the four endpoints of the line, and the direction you want the arrow to point.  1 is right and 2 is left.  It could be expanded to also include up and down, and probably diagonals also.

Author

Commented:
It should be possible to draw the arrow in ANY direction, at
ANY angle. There should be no need to pass a direction value
to the function as the direction is determined by the position
of the start and end points of the line. Thanks for trying though:)

Commented:
Following subroutine draws an arrow head at the line end point. The sample is written to draw an arrow formed by two line sections, but you can modify it to draw with an arrow style you like. It assumes the usage of a type

Private Type LineType
    xStart As Integer
    yStart As Integer
    xEnd As Integer
    yEnd As Integer
End Type

as the argument.

Private Sub DrawLineWithArrow(MyLine As LineType)
    Dim xTemp As Single
    Dim yTemp As Single
   
    ' Rotation coefficients
    Dim sCos As Single
    Dim sSin As Single
    Dim xDiff As Integer
    Dim yDiff As Integer
   
    ' Arrow coordinates
    Dim xTip As Single
    Dim yTip As Single
    Dim xCorner1 As Single
    Dim yCorner1 As Single
    Dim xCorner2 As Single
    Dim yCorner2 As Single
   
    ' Arrow dimensions. Set them to comply with your scale.
    Const xOffset = 5 'Lenght
    Const yOffset = 2 'Width
   
    With MyLine
        ' Calculate rotation coefficients
        xDiff = .xEnd - .xStart
        yDiff = .yEnd - .yStart
        sCos = xDiff / Sqr(xDiff * xDiff + yDiff * yDiff)
        sSin = Sqr(1 - sCos * sCos)
        If yDiff < 0 Then
            sSin = -Abs(sSin)
        End If
        If xDiff < 0 Then
            sCos = -Abs(sCos)
        End If
       
        ' Calculate arrow coordinates assuming horizontally
        ' positioned arrow at the line end point
        xTip = .xEnd
        yTip = .yEnd
        ' Translate origo to the the arrow tip
        xCorner1 = -xOffset '.xEnd - xOffset - xTip etc
        yCorner1 = yOffset
        xCorner2 = -xOffset
        yCorner2 = -yOffset
        ' Rotate and translate points
        xTemp = xCorner1 * sCos - yCorner1 * sSin
        yTemp = xCorner1 * sSin + yCorner1 * sCos
        xCorner1 = xTemp + xTip ' translate to original coordinates
        yCorner1 = yTemp + yTip
       
        xTemp = xCorner2 * sCos - yCorner2 * sSin
        yTemp = xCorner2 * sSin + yCorner2 * sCos
        xCorner2 = xTemp + xTip ' translate to original coordinates
        yCorner2 = yTemp + yTip
       
        'Draw line
        Picture1.Line (.xStart, .yStart)-(.xEnd, .yEnd)
        ' Draw arrow
        Picture1.Line (xTip, yTip)-(xCorner1, yCorner1)
        Picture1.Line (xTip, yTip)-(xCorner2, yCorner2)
    End With
End Sub

Commented:
That's the only thing I couldn't come up with is the formula to calculate the endpoints from the given angle.  Been too many years since Trig.

Author

Commented:
I'm afraid the solution doesn't work. The line:

sCos = xDiff / Sqr(xDiff * xDiff + yDiff * yDiff)

will produce an overflow error for all but the tiniest of lines, and even for the tiny lines, I see no arrow head.

I do appreciate the effort made in writing this answer however.
Commented:
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Commented:
Ooops .....

I meant to write, change all variable declarations having type integer to type single or double.

Sorry about that.

Author

Commented:
Great! It works perfectly now. Thankyou very much :)

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