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| Title | Draw an arrowhead on a line |
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| Keywords | arrow, arrowhead, line, draw |
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| Categories | Graphics |
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Use the geometry of the line to figure out how to draw the arrowhead. Suppose a line connects points (X1, Y1) and (X2, Y2). Then the vector (where dx = X2 - X1 and dy = Y2 - Y1) points in the direction of the line. The vectors and <-dy, dx> are perpendicular to the line.
The DrawArrow routine divides dx and dy by the length of the vector to get a unit vector (of length 1). It multiplies by an arm length to give the program control over ho long the arrowhead's sides are.
The routine then adds <-dx, -dy> to the perpendicular vectors and <-dy, dx> to get vectors pointing out and backwards, making the arrowhead.
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Private Sub DrawArrow(ByVal x1 As Single, ByVal y1 As _
Single, ByVal x2 As Single, ByVal y2 As Single, ByVal _
arm_length As Single)
Dim dx As Single
Dim dy As Single
Dim length As Single
Line (x1, y1)-(x2, y2)
dx = x2 - x1
dy = y2 - y1
length = Sqr(dx * dx + dy * dy)
dx = dx / length * arm_length
dy = dy / length * arm_length
Line (x2, y2)-Step(-dx - dy, -dy + dx)
Line (x2, y2)-Step(-dx + dy, -dy - dx)
End Sub
Private Sub Form_Paint()
DrawArrow 200, 200, 3000, 2000, 200
End Sub
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