Get the number of pixels

// Get the number of pixels on the X- and Y-edges of
// a unit square centered at (0.0, 0.0, 0.0), in
// world coordinates.
//
AcGePoint3d center(0.0, 0.0, 0.0);
AcGePoint2d area;
pV->viewport().getNumPixelsInUnitSquare(center, area);
// If the area values are negative, then we are in
// perspective mode and the center is too close or
// in back of the viewport.
//
if (area.x > 0.0) {
// Print out the number of pixels along the
// Y-axis of the unit square used in
// getNumPixelsInUnitSquare.
//
AcGeVector3d norm(0.0, 0.0, 1.0);
AcGeVector3d dir(1.0, 0.0, 0.0);
char buf[100];
sprintf(buf, "%7.3lf", area.y);
pV->geometry().text(center, norm, dir, 1.0, 1.0, 0.0, buf);
// Draw a circle that depends on how big the circle
// is in the viewport. This requires
// figuring out the fewest number of segments needed
// by a polyline so that it doesn’t look segmented.
//
// The worldDraw() and viewportDraw() of
// an entity in a viewport are only called during a
// regen and not necessarily during a ZOOM or PAN.
// The reason is that a regen produces something
// akin to a very high resolution image internally,
// which AutoCAD can zoom in or pan around. That is,
// until you get too close to this image or any of
// its edges, at which point a regen is internally
// invoked for that viewport and a new internal
// image is created (ready to be mildly zoomed and
// panned).
//
double radius = 0.5;
double half_pixel_hgt = 2.0 / area.x; // In WCS
int num_segs = 8;
double angle = two_pi / num_segs;
if (half_pixel_hgt > radius / 2) {
// The circle is approximately the same or less
// than the size of a pixel. So, generate a very
// small octagon.
//
num_segs = 8;
} else {
// Given a circle centered at the origin of a
// given radius in the XY-plane, and given a
// vertical line that intersects the X-axis at
// ’radius - half a pixel’, what is the angle
// from the X-axis of a line segment from the
// origin to the point where the vertical line

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