Calculating the angle of a Line in a circle(resolved)

[dglienna]

Or swap x2 and x1 of x2>x1, and the same for y

[paralinx]

Or swap x2 and x1 of x2>x1, and the same for y

I tried this also and I get the same exact thing for whichever I try

[moeur]

Private Function GetAngle(X1 As Long, Y1 As Long, X2 As Long, Y2 As Long) As Double
    Dim PI As Double
    Dim theta As Double
    Dim deltaX As Long
    Dim deltaY As Long
    'get angle of line in radians
    'deltay/deltax = tan(angle)
    deltaY = Y1 - Y2
    deltaX = X2 - X1
    PI = Atn(1) * 4
    'adjust to our coordinate system
        If deltaX = 0 Then
            'fix division by zero errors
            If Y1 > Y2 Then
                theta = 180
            Else
                theta = 90
            End If
        ElseIf deltaX > 0 And deltaY >= 0 Then '1st quadrant
            theta = Atn((Y1 - Y2) / (X2 - X1))
        ElseIf deltaX < 0 And deltaY >= 0 Then '2nd quadrant
            theta = Atn((Y1 - Y2) / (X2 - X1)) + PI
        ElseIf deltaX < 0 And deltaY < 0 Then '3rd quadrant
            theta = Atn((Y1 - Y2) / (X2 - X1)) + PI
        ElseIf deltaX > 0 And deltaY < 0 Then '4th quadrant
            theta = Atn((Y1 - Y2) / (X2 - X1)) + 2 * PI
        End If
    
    'convert to degrees
    'there are 180 degrees per PI radians
    'if theta < 0 then theta =
    GetAngle = theta * 180 / PI
End Function

[paralinx]

great thanks moeur

[dglienna]

moeur, could you possible explain that? I thought that it had something to do with quadrants, but didn't want to try to guess at the answer. If not, that's ok, also. I was thinking that 0 degrees was at 9'oclock, and that was the issue. Maybe I was close.

[moeur]

The problem is how the ArcTangent is defined
-90° < Atn(x) < 90°
for
-infinity < x < infinity

But that is not what we wanted so I had to adjust

[dglienna]

Well, I wish that I could have seen an explanation, but I found this link, and it didn't help much.

http://mathworld.wolfram.com/InverseTangent.html

I looked up tangent, and saw the same images.

http://mathworld.wolfram.com/Tangent.html

I guess I don't know what I'm looking at.

I used to know the formula to draw a circle with COS and SIN, so thought this wouldn't be too hard to grasp