Trying to understand how to read object coordinates flags from xmap

[wilmer100101]

Hi,

How does the flags work really? I did read about them on the wiki, I'm used to Java, so doesn't understand the c++ code so well.

But how do I know which is the control points for my bézier calculation when reading the xmap file? I haven't found any logic in it really, it seems as sometimes it's the coordinate that's before and after the node, but sometimes it just jumps over coordinates, a bit weird.

I also got a bit scared when seeing this in the code:

mapper/src/core/objects/object.cpp

Line 1621 in 3d5bc45

out_pfactor = -(126*P0x*pow(Q2x,3.0)*pow(sp,3.0) - 49*pow(P0x,2.0)*pow(Q3x,2.0) - 88*pow(P0x,2.0)*pow(Q2y,2.0) - 88*pow(P0y,2.0)*pow(Q2x,2.0) - 88*pow(P0x,2.0)*pow(Q3y,2.0) - 88*pow(P0y,2.0)*pow(Q3x,2.0) - 49*pow(P0y,2.0)*pow(Q2y,2.0) -

// Wilmer

[dg0yt]

How does the flags work really? I did read about them on the wiki, I'm used to Java, so doesn't understand the c++ code so well.

But how do I know which is the control points for my bézier calculation when reading the xmap file? I haven't found any logic in it really, it seems as sometimes it's the coordinate that's before and after the node, but sometimes it just jumps over coordinates, a bit weird.

It is simple: Basically almost everything is attached to the first point of a (straight or curved) primitve. With beziers, there are start point (on path), first handle, second handle, end point (on path. You can sort-of see it in the symbol editor:

So the first point carries a curve start property. It is the lowest bit of the flags.

mapper/src/core/map_coord.h

Lines 77 to 96 in 3d5bc45

	/**
	* These flags provide extra information on each coordinate in a path.
	*
	* Don't change the values, they are used in import/export.
	*/
	enum Flag
	{
	CurveStart = 1 << 0,
	ClosePoint = 1 << 1,
	GapPoint = 1 << 2,
	//unused 1 << 3,
	HolePoint = 1 << 4,
	DashPoint = 1 << 5,
	//...
	// Special masks for VirtualPath::copy().
	// CurveStart is handled explicitly there.
	MaskCopiedFlagsAtStart = GapPoint | DashPoint,
	MaskCopiedFlagsAtEnd = GapPoint | DashPoint | HolePoint | ClosePoint,
	};
	Q_DECLARE_FLAGS(Flags, Flag)

It is really written out here:

mapper/src/core/map_coord.cpp

Lines 220 to 229 in 3d5bc45

	void MapCoord::save(QXmlStreamWriter& xml) const
	{
	XmlElementWriter element(xml, XmlStreamLiteral::coord);
	element.writeAttribute(literal::x, xp);
	element.writeAttribute(literal::y, yp);
	if (fp)
	{
	element.writeAttribute(literal::flags, Flags::Int(fp));
	}
	}

---

I also got a bit scared when seeing this in the code:

mapper/src/core/objects/object.cpp

Line 1621 in 3d5bc45

out_pfactor = -(126*P0x*pow(Q2x,3.0)*pow(sp,3.0) - 49*pow(P0x,2.0)*pow(Q3x,2.0) - 88*pow(P0x,2.0)*pow(Q2y,2.0) - 88*pow(P0y,2.0)*pow(Q2x,2.0) - 88*pow(P0x,2.0)*pow(Q3y,2.0) - 88*pow(P0y,2.0)*pow(Q3x,2.0) - 49*pow(P0y,2.0)*pow(Q2y,2.0) -

Off-topic for the file format. This is for the operation of deleting the point between two bezier segments.

[wilmer100101]

Okey, when you say "handle" is that as a control point then?

Because when I read the format, does it seem to me that it is control point, node point (the main point), and then an control point, which doesn't make so much sense.

Please see example below:

[dg0yt]

Okey, when you say "handle" is that as a control point then?

Yes. My language was taken from the user interface.

Because when I read the format, does it seem to me that it is control point, node point (the main point), and then an control point, which doesn't make so much sense.

I don't see where you get this impression. The only relevant thing is that the last point of the first curve is the first point of the second curve.

Please see example below

• Points 1-4 form a bezier. (Point 1 has flags.)
• Points 4-7 form a bezier. (Point 4 has flags.)
• Points 7-10 form a bezier. (Point 7 has flags.)
• Points 10-11 form a straight line. (Point 10 has no flags.)

The path is not closed.

• Point 11 is different from point 1.
• There is no ClosePoint flag at point 11.

[dg0yt]

The actual calculation and drawing of the bezier is done by https://doc.qt.io/qt-6/qpainterpath.html#cubicTo.