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[UV
Edit - Polygon Mode]
Works with the currently selected
Polygons, or all Polygons of the mesh, if none are selected.
This command is very handy
for creating symmetrically mapped UVs on a symmetrically modelled
mesh. If you lost half of your mapping through using a Symmetry
Object, you can use this command to fix up the UVs for the polygons
of the new half. You can also use this after tweeking one side
or the other by hand to get those tweeks copied to the other
side.
This command has a few options
in how it works. To best describe those options, it will help
to give some background information...
There is a command within BodyPaint
named "Mirror U". When you use this command,
the currently selected polygons are 'flipped' in place
from left to right. An analogy might be that you pick up a card
off a deck, flip it over and place it back on top of the deck.
Put another way, the polygons are flipped from side to side about
some axis and the position (center of rotation) of that flipping-axis
is the average center of the selected polygons. This new "UV
Symmetry" command performs a similar function, but with
several differences in operation...
The first major difference
is that with UV Symmetry, you select polygons that are already
mapped, oriented and placed where you want them. The UV Symmetry
command tries to find the matching-but-mirrored polygons on the
other side of the mesh and mirrors (modifies) the UV mapping
of those polygons - not the ones that are selected.
The other differences have
to do with how the flipping-axis is determined (the point
about which the mirroring/reflection/flipping takes place)...
Default mode:
By default, the flipping-axis
is placed at 0.5, which would be the center of the UV screen
space (which goes from 0.0 on the left, to 1.0 on the right).
This means that if one of a selected polygon's UV vertices was
at 0.7 (0.2 greater than 0.5) on the U axis, the mirrored
UV vertex would end up at 0.3 (0.2 less than 0.5). An
analogy for this mode might be like picking up a card from a
deck, flipping it over and placing it to the side of the deck
(but exactly where the flipped card ends up depends on the position
of the deck - more on this below).
Shift Key Depressed:
If you are holding the [SHIFT]* key, this command tries to do something more
clever with the flipping-axis. An anology for this mode is more
like turning the page of a book or unfolding a flyer... the two
sides are still connected at the center.
The details of how this works
would probably best be described using a video tutorial (I'll
try to some up with one), but for here, I'll try to describe
it with an example...
Let's assume that we have a
humanoid head model. At some point, it was UV-mapped, but then
it was split in half and put into a Symmetry Object for further
modelling work. When the model was split in half, we lost half
of the polygons and half of the UV mapping. Now we're ready to
make the model whole again for export, so we collapse (Make Editable)
the Symmetry Object. When we do that, we get the other half of
the polygons back, but those new polygons are using a duplicate
copy of the UV mapping from the original polygons. The idea is
that we want the new polygons to have thier own UV mapping, which
is symmetrically mirrored from the other side of the mesh.
So, at this point, we have:
- a humanoid head mesh.
- half of the mesh's polygons
and vertices are on the POSITIVE-X (PX for short) side
of the mesh and the other half of the polygons are on the NEGATIVE-X
(NX) side of the mesh.
- the UV mapping of the head
is all on one side or the other (let's assume the PX side
for discussion purposes).
- with a typical UV mapping
of a humanoid head (Cylindrical-style), the center of the face
would be in the center of the mapped section and the left and
right edges of that mapping would be a 'seam' that ran up the
back of the skull - note that that seam/split would be at vertices
in the center of the mesh in the back of the head (this
is important for later...)...
- ...but since we split the
mesh in half and then re-joined it, both the PX and NX sides
of the mesh are now using the PX side of the UV mapping.
The mapped section we're left with goes from the center of the
nose on the left-most side of the mapped area to the seam at
the back of the skull on the right-most side of the mapped area.
Note that both the left-most and right-most UV polygons/vertices
correlate to mesh polygons/vertices that are at the center
of the mesh X-axis.
...so, now we want to flip
the NX uv polygons (which are currently on the PX side) over
to the NX side, where they belong.
So you select the PX polygons
(which are already correctly mapped) and click on "UV Symmetry"
with no keys pressed. Since the default mode of the command
puts the flipping-axis at 0.5, if the center of the nose
mapping (left-most edge) was exactly at 0.5, then you'd get a
perfectly symmetrical mapping, with the seam that runs up the
center of the face effectively 'stitched' together (assuming
that edge was a straight/vertical line). If the left-most edge
was at a position greater than 0.5, you'd have a 'gap' up the
center. If it was less than 0.5, you'd have some overlap between
the PX and NX sides of the mapping. Now for the 'clever' part...
If you hold the [SHIFT]* key down, the plugin will try to do a better
job of stitching the seam in the center, regardless of the position
of the current/existing mapping. To do this, the plugin can't
magically know 'how' you uv mapped your mesh, so it has to make
some assumptions about what you're trying to do, in order to
set up an appropriate flipping-axis...
- it assumes you have some Center
Polys selected (polygons that contain vertices which are
at the center of your mesh - have an X value of 0.0). If there
are no Center Polys selected, it just uses 0.5 as the flipping-axis.
- it assumes that you want the
'center' of the resulting uv mapping stitched up (or at
least as close as possible, without overlaps).
- it scans the list of selected
polygons, looking for Center Polys and keeps track of
the left-most U position (MinU) used by a Center
PX Poly, as well as the right-most position (MaxU)
used by a Center NX Poly.
- it then makes 2 more passes
through the selected polygon list...
- "1st pass" for flipping
from PX->NX, it uses MinU as the flipping-axis
- "2nd pass" for flipping
from NX->PX, it uses MaxU as the flipping-axis
...note that in our example,
we have the PX side (right side of the screen) of the mapping,
and the left-most U position (MinU) of that mapping correlates
to the center of the nose. So we see that this situation will
get handled by the "1st pass" above. If we had deleted
the other side of the polygons, then the right-most U position
(MaxU) would correlate to the center of the nose and that situation
would be handled by the "2nd pass".
I realize that all of this
may be confusing and more than you care to know, so the short
explanation is: Just try it :). If it doesn't do what you expect,
then use the command without the [SHIFT] key and move/stitch
things up manually.
The longer explanation is:
if you understand the gory details above, it might help explain
'why' it doesn't work as you expect it to in some situation or
another (your mapping might be flipped backwards, you might have
selected the wrong side of the mesh or you might have some Center
Poly in some odd place on the map selected that's throwing
things off, etc.).
The one thing to keep in mind
about this mode is: If your selection contains any Center
Polys (any polygon that contains a mesh vertex who's
X position is 0.0), then the plugin will try to position the
mirrored polys as if it was unfolding two halves of a piece of
paper.
Ctrl Key Depressed:
At the risk of adding to the
confusion... by default, when the command completes, the "Current
Selection" hasn't changed. If you hold the [CTRL]* key, the newly-altered polygons will be selected
when the command completes.
** TIP:
If you are getting ready to
collapse your Symmetry Object to make a whole mesh...
1. before you hit the
"Make Editable" button, do a "Select All"
on your mesh in polygon mode.
2. hit the "Make Editable" button.
3. your 'half' mesh will still be selected, so.. before you do
anything else, create a new polygon selection ("Selection->Set
Selection") and name it "left-side" (or "right-side").
4. "Selection->Invert".. now the other (new) half
is selected, so make another polygon selection and name that
one appropriately.
...NOTE: if you do step 3 BEFORE
you do step 2, your selection get's updated with the entire mesh
after the Make Editable - you don't want that.
Now you have easy access to select one side of your mesh or the
other for future "UV Symmetry" operations.
** NOTE: As mentioned in the UV Tile
commands documentation, I realized that I was using the [SHIFT]/[CTRL]
keys inconsistently on some of the commands... the new/current/future
paradigm I'm trying to follow is "[SHIFT] = include
xx, [CTRL] = control or modify direction/operation".
Unfortunately, this command
(and others) is still using the opposite meaning for those keys...
this may change in a future update.
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