SOLVED Bend Deformer Using C++

@zipit @mfersaoui not quite; the pivot of the rotation is also changing (only along one axis, but still...), and it's not a linear movement but some exponential one between 0 (approaching only) and infinity (when no bend). The infinity one may also be tricky numerically.

I have an idea how to solve (my Google-fu seems weak on this) but haven't tried in praxis yet.

okay, calculate with me...

The arc length L for an angle alpha on a circle with radius r is L = 2* pi * r * alpha / 360
(assuming alpha is in degree). alpha is known; it is the bend angle.
The arc length is also known - it's the distance of the bending point to the center of the bend
(assuming we want to keep that length constant).
The radius is actually the wanted value. So we transform
L * 360 = 2 * pi * r * alpha
(L * 360) / (2 * pi * alpha) = r
Obviously, this is numerically bad since with alpha approaching 0, r is approaching infinity. But maybe we can solve this in the transformation and get rid of either alpha or r.

The rotation of the target coordinate system (the object to place on the bend) is obviously alpha itself.
The position p of the target needs to be moved according to sin and cos of alpha on the circle with radius r.

Remember that all of this needs to be expressed in the coordinate systems of either the object, the world, or the bend deformer, which makes the calculation perhaps a bit awkward.

For simplification, we'll assume that world, bend, and object coordinates are all the same.

Now you can draw a circle with radius r and check where a point p is going. Let's just look at the point p = (L,0) - the farthest centered point of our object, or the center of the coordinate system of out object if you want to move a whole object.

Then p'.x is going to be r * sin(alpha), and p'.z will be r - r * cos(alpha), as per the definitions of sine and cosine.

And that's all there is! Okay, after you did the necessary coordinate transformations between the base coordinate systems and adapted the calculation for other points than p, but that's homework.

Here I made a little scene where a Python tag does the calculation. A flattened cube is bent by a bend deformer; a torus primitive is moved accordingly to stay flush with the left edge of the cube. Note that the calculation for the torus position and rotation is done solely through the Python tag, whose only input the bend deformer's angle is, so the Python tag is actually replicating the bend deformer functionality.


The main part is the code of the Python tag (I'm calculating with radians here so don't wonder why there is no pi; also the bend deformer in my scene is pointing to the negative x so we have additional minus signs:

import c4d
from math import sin, cos

def main():
    torus = op.GetObject()
    source = torus.GetPred().GetDown()
    strength = source[c4d.DEFORMOBJECT_STRENGTH]
    originx = -400.0
    originz = 0.0
    if strength == 0.0:
        targetx = originx
        targetz = originz
        roth = 0.0
        alpha = strength
        radius = originx / alpha
        targetx = radius * sin(alpha)
        targetz = -(radius - radius * cos(alpha))
        roth = -alpha
    torus[c4d.ID_BASEOBJECT_REL_POSITION,c4d.VECTOR_X] = targetx
    torus[c4d.ID_BASEOBJECT_REL_POSITION,c4d.VECTOR_Z] = targetz
    torus[c4d.ID_BASEOBJECT_REL_ROTATION,c4d.VECTOR_X] = roth

Obviously this is a very simplified sample that works only for this scene, but you can adapt the calculation for yours.

Thank you so much for your help and for your detailed explanation, I started to testing your code in python to better understand and now I will try to adapt it to my project in c++. If I have a problem I return to this topic.
Thanks again.

Thanks to you, I have obtained the desired result.
In my project the "strength" and the "originx" values is not constant, also the total count of the lights object is not constant. So I made the necessary changes on your code.
Here is the final code:


AutoAlloc<BaseObject>	containertPtr(Onull);
AutoAlloc<BaseObject>	parentlighstPtr(Onull);
AutoAlloc<BaseObject>	recPtr(Osplinerectangle);
AutoAlloc<BaseObject>	bendPtr(Obend);

if (!containertPtr || !recPtr || !parentPtr || !bendPtr)
	return false;

// Set names

// Variables
Int32 Count = 7;

Float	Xpos, Ypos,
		Width = 150.0,
		Height = 250.0,
		interval = 40.0;

Ypos = Height / 2;

// Rectangle object

// Bend object
Float fullWidthSize = (Width*Count) + interval*(Count - 1);
Float	bendStrength = 90.0;

bendPtr->SetParameter(DEFORMOBJECT_SIZE, Vector(Height, fullWidthSize / 2, 10.0), DESCFLAGS_SET_0);
bendPtr->SetParameter(DEFORMOBJECT_STRENGTH, bendStrength, DESCFLAGS_SET_0);
bendPtr->SetParameter(DEFORMOBJECT_ANGLE, DegToRad(-90.0), DESCFLAGS_SET_0);
bendPtr->SetAbsRot(Vector(0, 0, DegToRad(-90.0)));
bendPtr->SetAbsPos(Vector(fullWidthSize / 4, Height / 2, 0.0));

Float strength, alpha, radius, originx, originz = 0.0, targetx, targetz, roth, step;

Float	centerx = fullWidthSize/2;

for (Int32 i = 0; i < Count; i++)
	AutoAlloc<BaseObject>	InstancePtr(Oinstance);
	AutoAlloc<BaseObject>	ExtrudePtr(Oextrude);
	AutoAlloc<BaseObject>	LightPtr(Olight);

	if (!InstancePtr || !ExtrudePtr || !LightPtr)
		return false;
	Xpos = (Width*i) + (interval*i) + (Width / 2);

	originx = centerx - Xpos;
	originx = originx*-1;

	step = centerx / originx;
	strength = bendStrength / step;

	if (strength == 0.0) {
		targetx = originx;
		targetz = originz;
		roth = 0.0;
	else {
		alpha = strength;
		radius = originx / alpha;

		targetx = radius * sin(alpha);
		targetz = -(radius - radius * cos(alpha));

		roth = -alpha;
	// Set names
	ExtrudePtr->SetName("Extrude_" + String::IntToString(i));
	InstancePtr->SetName("Instance_" + String::IntToString(i));
	LightPtr->SetName("Light_" + String::IntToString(i));

	// Light object
	LightPtr->SetParameter(LIGHT_TYPE, 8, DESCFLAGS_SET_0);
	LightPtr->SetParameter(LIGHT_AREADETAILS_SIZEX, Width*0.9, DESCFLAGS_SET_0);
	LightPtr->SetParameter(LIGHT_AREADETAILS_SIZEY, Height*0.9, DESCFLAGS_SET_0);

	// Instance object
	InstancePtr->SetParameter(INSTANCEOBJECT_LINK, recPtr, DESCFLAGS_SET_0);

	// Extrude object
	ExtrudePtr->SetParameter(EXTRUDEOBJECT_MOVE, Vector(0, 0, 0), DESCFLAGS_SET_0);
	ExtrudePtr->SetAbsPos(Vector(targetx, Ypos, targetz));
	ExtrudePtr->SetAbsRot(Vector(roth, 0, 0));



I'm not sure why my suggested solution didn't work. Did you apply the Bend to a Matrix object and then Clone onto that Matrix (Cloner in Object mode targeting the Matrix)? The Bend should modify the Matrix positions/rotations and the Cloner should pick up those modified positions for it's children (the lights).

Rolling your own bend algorithm definitely has its advantages over this, but I was surprised to hear that you got exactly the same result.


My bad, I misunderstood. I just retest and it's working well using Matrix and Cloner object.
Thanks you so much for your help and for reminding me.

Not that much to add it here I think everything was already said.

But I just would like to remind you to use the Q&A functionality

Sorry, but I haven't the ability to mark this post as solved. I don't see the button "Mark this post as the correct answer".

Yes because I've done it 🙂