How to find Edge Direction?

[mayarulezzz]

Hi everyone and sorry if i've been posting like crazy but this plugin development thing is so exciting...

I started by creating a simple edgeSlide Node for sliding one edge across the connected edges. It is already working but with one problem, while some edges flow in one dir the others flow in other, Is there any way of knowing an edge first point in order to get it's direction?

Thanks for all the help

[deane]

Edges can be shared. A shared edge can (and most likely will) have different directions on different faces. So an edge by itself doesn't have any intrinsic direction. It only has direction in association with a given face.

If you have a face, then you can retrieve the face's vertex indices using MFnMesh::getPolygonVertices() and the edge's vertex indices using MFnMesh::getEdgeVertices() then step through the polygon's vertices in order to see which of the edge's vertices you find first.

[mayarulezzz]

hey deane,

thanks for your reply, it seems you're the only one that likes answering my questions .

According to that post of yours in order to get all the slides to slide the same direction i better check all which are connected and then propagate that direction to all the connected ones no? In irder to do that i guess i need to rethink my strategy. Thanks a lot for all the help.

Best regards,

MayaRulezzz

[joojaa]

Im not supprised deane ois the only one answering because theres a shortage of people who.

A) know maya
know how to use maya API
C) do not program things allready implemented in maya (youd be supprised how often you se people turning to api without looking around, or even understanding maya at all)
D) have the time to answer your questions, because theyre more likely programming something.

[deane]

it seems you're the only one that likes answering my questions

Everyone else is probably out doing their christmas shopping.

in order to get all the slides to slide the same direction i better check all which are
connected and then propagate that direction to all the connected ones no?

I don't really understand what you're saying.

When you talk about an edge's "direction", are you talking about it's worldspace direction, as if you treated it like a vector? Or are you talking about the ordering of its vertices as you travel counter clockwise around one of the faces of which it is part?

To take an example, let's say that we have a poly face which is a perfect square, having vertices A, B, C and D, like so:

A ---- D
| |
B ---- C

Normally, the vertices of a face are traversed in a counter-clockwise direction. So the left edge of the square would be called AB and the right edge CD. Similarly, the "direction" of the left edge is downward, from A to B while the direction of the right edge is upward, from C to D.

You say that you want "to get all the slides to slide the same direction". By that do you mean that if you were sliding along the left and right edges of this square you would want to slide counter-clockwise in both cases -- that is, downward on the left and upward on the right? Or do you mean that you want to slide in the same worldspace direction -- that is, either upward on both edges or downward on both?

If it's the worldspace direction you're concerned about, that's pretty easy to work out. Subtract one end of the edge from the other to get a vector. Do the same with the other edge, then take the dot product of the two vectors. If the result is negative then flip the ends of one of the edges and they'll now both be in the same direction (or as close as possible). If the result is 0 then the edges are perpendicular and it's up to how how you want to handle them since "same direction" becomes meaningless at that point.

I suppose a third possibility is that you want to slide along both edges away from some common point. For example, in the square above, sliding along the left and bottom edges away from vertex B. If that's the case then just order the edge endpoints according to their distance from the common point.