Like edge intersecion in Vatti --how many 4 or 8 ---

[Ignorant]

[Jay Tee]

No, those kinds if intersections are impossible. That is a direct consequence of the definition of left / right edges: The inner area of the polygon is located to the right of a left edge (and vice versa). If a left edge intersected a left edge of the same polygon type (subject / clip), their definitions of inside / outside would contradict for the area between them.

[Ignorant]

Jay, what about self intersecting polygons ?do they have inside outside
?(odd/even winds only).

On Thu, Feb 6, 2020 at 4:44 PM Jay Tee jay-tee@users.sourceforge.net
wrote:

No, those kinds if intersections are impossible. That is a direct
consequence of the definition of left / right edges: The inner area of the
polygon is located to the right of a left edge (and vice versa). If a left
edge intersected a left edge of the same polygon type (subject / clip),
their definitions of inside / outside would contradict for the area between
them.

---

Like edge intersecion in Vatti --how many 4 or 8 ---
https://sourceforge.net/p/polyclipping/discussion/1148419/thread/4542a3b35b/?limit=25#5f29

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[Ignorant]

I expectd that but …..
I decided to put guards in the Boolean op codes I have..
They fail.!
What happens when one has multiple input polygons for both subject and Clip?.
Sent from Mail for Windows 10

From: Jay Tee
Sent: 06 February 2020 16:44
To: [polyclipping:discussion]
Subject: [polyclipping:discussion] Like edge intersecion in Vatti --how many 4or 8 ---

No, those kinds if intersections are impossible. That is a direct consequence of the definition of left / right edges: The inner area of the polygon is located to the right of a left edge (and vice versa). If a left edge intersected a left edge of the same polygon type (subject / clip), their definitions of inside / outside would contradict for the area between them.

Like edge intersecion in Vatti --how many 4 or 8 ---

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[Jay Tee]

Yes, it is completely the same for self-intersecting polygons.

[Ignorant]

?. What is the relation between Left/right of edge and side of edge ..?.I have a damaged clipper which gives proper output but testing for inequality of sides for ( e1 polygon type ==e2 polygon type) fails.filtering the intersection does NOT help.!

[Jay Tee]

I'm afraid I don't understand your question. Left / Right are the two possible sides of an edge. That classification indicates if the edge is left or right to the interior of its original polygon (subject or clip).

[Ignorant]

I want to understand HOW we get the L/R labels of a edge.
For Within Beam intersections sometimes ...
e1->PolyType==e2->polytype but e1->side != e2->side fails.

 The code is mutated from  Angus clipper ..but works...so...!!??

I confirm by area coverage of filled region in output with anothe on/off parity clipper...

here is the code fragment :

// ======Filter   lifted from clipperv2==============
    const bool e1_windcnt_in_01 = e1Wc == 0 || e1Wc == 1;
    const bool e2_windcnt_in_01 = e2Wc == 0 || e2Wc == 1;
    // ---Global Filter---

if ((!e1IsHot && !e1_windcnt_in_01) || (!e2IsHot && !e2_windcnt_in_01))
return;
// =================================================
if(e1->PolyTyp ==e2->PolyTyp)
{ //guard ----------------feb 2020--------------------------
///It seems that bound type and side are different attributes.....!@#$...
if( e1->Side == e2->Side) //LC X LC,LS X LS RC X RC RS X RS should NOT occur ??
{ // within beam ?? Across scan line
if(XWithinBeam)
CLipperOut<< "poly sides unexpected"<<std::endl;
// return;
}
}

[Jay Tee]

Maybe the side attribute indicates (for contributing edges) if they form the left / right bound of their associated output polygon? That classification can differ from the actual bound type of the edge.

And regarding your question on how to obtain the left / right bound type label: When a new minimum bound is inserted into the AEL, one counts the edges of the same polygon type (left / right) that precede the new bound. If their number is even, the first bound edge is labeled 'left' and the second one 'right'. Otherwise, those labels swap places.

[Ignorant]

Thanks. That will comfort me to switch off the guard at this spot.
I am trying to get a good description of the edges which lead to vertices being added to output polygons bypassing the edge X edge intersections.[before horizon,after horizon,attopscanbeam..).
If they are described properly then vattis method can be coded as a simple collection of rendering routines(for odd/even coding,Angus Windings NOT included).

[Ignorant]

What is special about the XOR command.I have a vatti like clipper in which the XOR works as indicated.BUT when I do edge budles the XOR bundles somehow deviate to indicate Left Intermediate/RIGht Intermediate (I ignrore both).The areal output covergae is still correct.For the
other 3 boolean ops no extra commands are generated(within beam intersections).So I was wondering what is special about XOR.?
Clipper2 has so much internal cleaning that it is (for me) scarry to trace what is happening for XOR within the Murta Quadrants..odd/even parity.