<?xml encoding=”UTF-8″>By Xiaodong Liang
Issue
How can I have a custom entity support the AutoCAD DIVIDE command?
Solution
To have a custom entity support the DIVIDE command , you must first must derive from AcDbCurve or one of its derived classes. Then override the following as a minimum implementation to support the DIVIDE command, e.g.
<pre>Acad::ErrorStatus getStartParam(double& startParam) const;<br>Acad::ErrorStatus getEndParam(double& endParam) const;<br>Acad::ErrorStatus getDistAtParam (double param, double& dist) const;<br>Acad::ErrorStatus getPointAtDist(double dist, AcGePoint3d& point) const;<br>Acad::ErrorStatus getPointAtParam(double param, AcGePoint3d& point) const</pre>
For a code sample on how to override these methods and to implement them in a custom entity, refer to polysamp sample in the ObjectARX SDK. This customer entity is a closed poly line e.g.
The relevant overridden methods are:
getStartParam (double& startParam) const
{
assertReadEnabled();
startParam = 0.0;
return Acad::eOk;
}
virtual Acad::ErrorStatus
getEndParam (double& endParam) const
{
assertReadEnabled();
endParam = 6.28318530717958647692;
return Acad::eOk;
}
double param,
double& dist) const
{
assertReadEnabled();
rx_fixangle(param);
double circumRadius =
(startPoint() – center()).length();
double alpha =
3.14159265358979323846 * 0.5 –
3.14159265358979323846 / mNumSides;
double sideLength =
2.0 * circumRadius * cos(alpha);
double includedAngle =
6.28318530717958647692 / mNumSides;
int numIncludedAngles =
int(param / includedAngle);
double theta =
param – numIncludedAngles * includedAngle;
if (theta > 1.0e-10) {
dist = sideLength * numIncludedAngles +
circumRadius * sin(theta) /
sin(3.14159265358979323846 – theta – alpha);
} else {
dist = sideLength * numIncludedAngles;
}
return Acad::eOk;
}
AsdkPoly::getPointAtParam(
double param,
AcGePoint3d& point) const
{
assertReadEnabled();
Acad::ErrorStatus es = Acad::eOk;
// Find out how many included angles “param” contains.
// Find that vertex, and the direction of the line defined
// by that vertex and the following vertex. Add the appropriate
// distance along that line direction to get the new point.
rx_fixangle(param);
double circumRadius =
(startPoint() – center()).length();
double includedAngle=
6.28318530717958647692 / mNumSides;
int numIncludedAngles =
int(param / includedAngle);
double theta =
param – numIncludedAngles * includedAngle;
double gamma =
3.14159265358979323846 * 0.5 +
3.14159265358979323846 / mNumSides – theta;
double distToGo =
circumRadius * sin(theta) / sin(gamma);
AcGeVector3d lineDir =
sideVector(numIncludedAngles);
AcGePoint3dArray vertexArray;
if ((es =
getVertices3d(vertexArray)) != Acad::eOk) {
return es;
}
if (theta > 1.0e-10) {
point = vertexArray[numIncludedAngles] + (distToGo * lineDir);
} else {
point = vertexArray[numIncludedAngles];
}
return es;
}
By these method, when DIVID command is executed, users input the segment number of division such as 10. AutoCAD will divide the poly along the sides and create the segment points.
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