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    Creating a Circle (spline) with varying number of points.

    Cinema 4D SDK
    python r20
    4
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    • P
      pim
      last edited by

      If I create a circle, it has always just 4 points.
      How can I create a circle (spline) with for example, 5 or 28 points?

      1 Reply Last reply Reply Quote 0
      • eZioPanE
        eZioPan
        last edited by eZioPan

        Hi @pim,
        As far as I know, there is no way to make a "perfect circle" with any type of spline in Cinema 4D.
        I search on the Internet, based on this answer: How to create circle with Bézier curves?.
        I write the following code to create a circular-like spline shape:

        import c4d, math
        #Welcome to the world of Python
        
        deg = math.pi/180.0
        
        def main():
            pCnt = 4             # Here is the point count
            radius = 200         # Here is the radius of circle
            subdAngle = 5*deg    # Here is the subdivision angle
        
            #Prepare the data
            tangentLength = (4/3)*math.tan(math.pi/(2*pCnt))*radius # single side tangent handle length
            pointPosLs = []
            tangentLs = []
            for i in range(0,pCnt):
        
                angle = i*(2*math.pi)/pCnt    # caculate the angle
        
                # caculate point position
                y = math.sin(angle)*radius
                x = math.cos(angle)*radius
                pointPosLs.append(c4d.Vector(x, y, 0))
        
                # tangent position
                lx = math.sin(angle)*tangentLength
                ly = -math.cos(angle)*tangentLength
                rx = -lx
                ry = -ly
                vl = c4d.Vector(lx, ly, 0)
                vr = c4d.Vector(rx, ry, 0)
                tangentLs.append([vl, vr])
        
            # init a bezier circle
            circle = c4d.SplineObject(pcnt=pCnt, type=c4d.SPLINETYPE_BEZIER)
            circle.ResizeObject(pcnt=pCnt, scnt=1)
            circle.SetSegment(id=0, cnt=pCnt, closed=True)
            circle[c4d.SPLINEOBJECT_CLOSED] = True
            circle[c4d.SPLINEOBJECT_ANGLE] = subdAngle
            
            circle.SetAllPoints(pointPosLs) # set point position
        
            # set tangent position
            for i in range(0, pCnt):
                circle.SetTangent(i, tangentLs[i][0], tangentLs[i][1])
        
            circle.Message(c4d.MSG_UPDATE)
        
            return circle
        

        You can try put this code in a Python Generator object to get the result.

        I'm not very sure about my answer, waiting for more convincing answers.

        1 Reply Last reply Reply Quote 2
        • M
          mp5gosu
          last edited by

          You may also want to take a look at the official Cinema 4D SDK for an example of a circle object: https://github.com/PluginCafe/cinema4d_cpp_sdk_extended/blob/master/plugins/cinema4dsdk/source/object/circle.cpp

          Though it's C++, the algorithm should be easily adaptable.

          1 Reply Last reply Reply Quote 3
          • S
            s_bach
            last edited by

            Hello @pim ,

            I guess you are talking about the "Circle" spline primitive? The generated spline has always 4 control points; there is no way to change that.

            But you could try to get the generated spline and apply the "Subdivide" tool. Whit that tool you can add additional points.

            Or you could, as @eZioPan and @mp5gosu and have shown, create the spline completely by yourself.

            best wishes,
            Sebastian

            MAXON SDK Specialist

            Development Blog, MAXON Registered Developer

            1 Reply Last reply Reply Quote 2
            • P
              pim
              last edited by

              Thank you all, great answers!
              I will take a different approach.
              I convert the circle to a spline and then divide that spline into the wanted number of points.

              -Pim

              1 Reply Last reply Reply Quote 0
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