C++ - How to get points of rotating cylinder? - c++

Question

I need the points of a "rotating cylinder". I've got some lines of a curve and looking for an implementation to calculate 16 points arount them to get a cycle. My implemenation looks like:
QPointF MappingModel::calcThicknessYarns(float fCurrentX, float fCurrentY, int iCurrentCounter)
{
QPointF nextPoint;
int iAmountOfThicknessYarns = 16;
float fSingleAngle = 360.0 / iAmountOfThicknessYarns;
float fCurrentAngle = fSingleAngle * iCurrentCounter;
nextPoint = getXY(fCurrentAngle, 1.0, 1.0, fCurrentX, fCurrentY);
return nextPoint;
}
and
QPointF MappingModel::getXY(float angle, float width, float height, float xOffset, float yOffset)
{
QPointF xy;
float FI = angle*PIdev;
xy.setX((width * qCos(FI)) + xOffset) ;
xy.setY((height * qSin(FI)) - yOffset);
return xy;
}
My looks like this:
http://www.directupload.net/file/d/3741/e8bafwni_jpg.htm
http://www.directupload.net/file/d/3741/tkykay7w_jpg.htm
As you can see, the the vertical cylinder works fine, but the curve is false

Answer 1

This may help.
It shouldn't be difficult to adapt Vertex to QPointF.
typedef struct {
double x;
double y;
} Vertex;
/**
* #param radius Radius of circle
* #param angle Degrees
* #return The offset of vertex from the center of circle given radius and angle
*/
Vertex getVerticeOffset(double radius, double angle) {
double yOffset = -radius*cos((90 - angle)*M_PI/180); // convert to radians
return Vertex({(angle >= 90 && angle < 270 ? -1 : 1) * sqrt(pow(radius, 2) - pow(yOffset, 2)), yOffset});
}