/**
* Compute the positions of the arrow head of the graphic's legs.
*
* @param dc Current draw context
* @param base Position of the arrow's starting point.
* @param tip Position of the arrow head tip.
* @param arrowLength Length of the arrowhead as a fraction of the total line length.
* @param arrowAngle Angle of the arrow head.
* @return Positions required to draw the arrow head.
*/
protected List<Position> computeArrowheadPositions(
DrawContext dc, Position base, Position tip, double arrowLength, Angle arrowAngle) {
// Build a triangle to represent the arrowhead. The triangle is built from two vectors, one
// parallel to the
// segment, and one perpendicular to it.
Globe globe = dc.getGlobe();
Vec4 ptA = globe.computePointFromPosition(base);
Vec4 ptB = globe.computePointFromPosition(tip);
// Compute parallel component
Vec4 parallel = ptA.subtract3(ptB);
Vec4 surfaceNormal = globe.computeSurfaceNormalAtPoint(ptB);
// Compute perpendicular component
Vec4 perpendicular = surfaceNormal.cross3(parallel);
double finalArrowLength = arrowLength * parallel.getLength3();
double arrowHalfWidth = finalArrowLength * arrowAngle.tanHalfAngle();
perpendicular = perpendicular.normalize3().multiply3(arrowHalfWidth);
parallel = parallel.normalize3().multiply3(finalArrowLength);
// Compute geometry of direction arrow
Vec4 vertex1 = ptB.add3(parallel).add3(perpendicular);
Vec4 vertex2 = ptB.add3(parallel).subtract3(perpendicular);
return TacticalGraphicUtil.asPositionList(globe, vertex1, vertex2, ptB);
}
/**
* Determine the positions that make up the arrowhead.
*
* @param dc Current draw context.
* @param startPosition Position of the arrow's base.
* @param endPosition Position of the arrow head tip.
* @return Positions that define the arrowhead.
*/
protected List<Position> computeArrowheadPositions(
DrawContext dc, Position startPosition, Position endPosition) {
Globe globe = dc.getGlobe();
// Arrowhead looks like this:
// _
// A\ | 1/2 width
// ________B\ _|
// Pt. 1 /
// C/
// | |
// Length
Vec4 p1 = globe.computePointFromPosition(startPosition);
Vec4 pB = globe.computePointFromPosition(endPosition);
// Find vector in the direction of the arrow
Vec4 vB1 = p1.subtract3(pB);
double arrowLengthFraction = this.getArrowLength();
// Find the point at the base of the arrowhead
Vec4 arrowBase = pB.add3(vB1.multiply3(arrowLengthFraction));
Vec4 normal = globe.computeSurfaceNormalAtPoint(arrowBase);
// Compute the length of the arrowhead
double arrowLength = vB1.getLength3() * arrowLengthFraction;
double arrowHalfWidth = arrowLength * this.getArrowAngle().tanHalfAngle();
// Compute a vector perpendicular to the segment and the normal vector
Vec4 perpendicular = vB1.cross3(normal);
perpendicular = perpendicular.normalize3().multiply3(arrowHalfWidth);
// Find points A and C
Vec4 pA = arrowBase.add3(perpendicular);
Vec4 pC = arrowBase.subtract3(perpendicular);
return TacticalGraphicUtil.asPositionList(globe, pA, pB, pC);
}