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We're back for the second installment on the topic
of using pre-fab scenery.
Last time we talked
about the basic concepts behind pre-fabs, drew up
some rough specifications for our own scenery
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started with a simple wall/niche block. Now we
need to add a little visual interest - through
textures! The image at the right shows our
creation as it should look when we're all done
- ready for whatever dungeon nasties inhabit
your game to move right in. It even has a spot
for their favorite boiling pot of delver
chilli! So, let's get to it, shall we?
First,
download the resource
file for this course! |
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Part
Three: UV Mapping Overview |
If you have a hard time
getting your head around the concept of UV mapping,
don't worry - a lot of people do. The good news is
that it really isn't that complex once you
understand the fundamentals. For those who need it
we will take a closer look at what UV mapping is and
how it works. The rest of you can just skip to the
next section.
| UV mapping, very simply,
specifies where the renderer should look for
texture information for a given point on a
model. UV space is limited - ranging from 0 to
1 in the U direction and from 0 to 1 in the V
direction (see image at right). If we specify
a UV co-ordinate of (0.25, 0.5) the renderer
will look into the texture and retrieve the
color of the pixel located one-quarter of the
way across and half way down the co-ordinate
space. Now that we know about UV space the
concept of UV mapping is very simple. Each
vertex of your model, in addition to having an
XYZ co-ordinate in 3D space, also has an UV
co-ordinate in texture (UV) space. |
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So, for a cube you might 'lay out' the UVs as
in the image to the right. Here, we've
'folded' the cube's faces so that they lay
flat in the plane. Boxes are easy, but what
about something a little more complex? Most
objects are easy to map as long as you keep
some simple rules of thumb in mind. The first
is that, the larger the area taken up by the
face in UV space, the more pixels you will see
on that face in the rendered image. In
general, you should keep all of the faces laid
out in UV space fairly proportional to their
sizes in 3D space - i.e. if a face is twice as
large in 3D space then it should be twice as
large in UV space. |
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This is a rule made to be broken, however. Some
areas of your models will naturally need more detail
than others. Areas of greater interest can be larger
in UV space, giving you more room for texturing - a
common example is for a human model, where the face
area is generally quite a bit larger than any of the
other parts (in fact, many modelers actually use a
separate map for the head altogether.)
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Another basic
pointer is to try to keep adjoining faces next
to each other. This will allow the texture to
flow naturally across seams and will lead to
fewer texturing artifacts. Of course, some
seams will be separated in order to get the
model to 'lay flat', as with our cube example
above. Finally, try to keep faces from
becoming too 'skewed' as this will distort the
texture applied to them. Of course, you can
sometimes use this to your advantage. On the
left is an example of a fairly complex UV map
laid out for one of my character models - a
Space Marine Terminator from Games Workshop. |
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Part
Four: Laying Out The UVs |
| UV mapping our wall should be
a breeze because it is a pretty simple model -
consisting mostly of a single front face and a
small rectangular 'flap' at the top. Your
first thought might be to make the UV
projection take up most of the texture space,
to get as many pixels as possible into play.
In this case that might cause us problems down
the road. Why? Because we have other models
that will be interacting directly with this
one - and some of those have more surface
area. Take a look at the Hallway End pre-fab
we mentioned last time. It has three wall
sections, each as large as this one. With the
UVs laid flat we will have much less space per
wall face - and that means that the pixels
won't quite match up next to this one. Take a
look at the image for a visual comparison.
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So, with this in mind we should probably lay out
this model's UVs a little smaller than we ordinarily
would. Getting started mapping is easy. Just open
the new gameSpace1.6 UV Editor and you'll see the
default layout as ‘automagically’ generated by
gameSpace. Not very impressive is it? That's okay,
no software can do this - we have to fix it by hand!
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If you have complex geometry, such as our
little niche, you might find your polygons are
a little out of whack in the UV Editor. 3D
software has a hard time dealing with polygons
with more than four sides. You should use the
Add Edges and Add Vertex tools to make sure
your model consists of reasonably shaped
quadrangles and triangles before you start
mapping. NEVER allow the software to
triangulate the model for you - it won't do it
correctly and will destroy your textures. The
image shows how our wall segment could be
divided.
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So, let's map the most important part first. It's
going to be hard to figure out which polygons are
which in the UV Editor until we get them sorted out
a bit so you will need to enter Point Edit mode in
the 3D window by right-clicking on the object. You
should now see the edges and vertices of your model.
Choose the Face Selection tool and select one of the
faces that make up the front of the wall. Then,
holding the CTRL key, click on each of the other
front faces one-by-one until they are all selected.
They are all in a plane so just click on the Planar
UV Projection icon and you should see a distorted
version of your wall in the UV Editor.
The UVs are distorted because gameSpace scaled your
selection to the entire texture space. We will need
to correct this by scaling it down. Click the Point
Scale tool from the UV Editor toolbar and, while
holding the left mouse button, scale the selection
until it's roughly the same proportions as your
original wall. Note that if you hold the right mouse
button instead the selection will scale uniformly,
keeping original proportions the same.
Believe it or not, we're mostly done. Using the same
technique, select the faces at the top of the wall
and scale them to roughly match the wall UVs. You
may also have to use the Point Rotate and Point Move
tools to get the UVs going in the right direction
and positioned properly. The image below shows the
wall top laid out and in position. Note that this
can just be done roughly at this point - we are just
'sorting out' the UVs for now, finding out what goes
where. When that step is complete we can clean
everything up.
Finally, let's do something with that niche. Select
the faces that make up the back of the niche and do
a planar projection. Scale the selection down and
move it out of the way. Now, map the inside edges of
the niche. The easiest way is to select the faces in
groups, based on how close to 'flat' they are. For
our example, the two faces at the top of the arch,
the two vertical faces on either side of the niche,
and the bottom face, were selected as groups and
projected as planar. Scaled down it looks like this:
Looks like we have all of the faces identified and
in their proper places. So, now the tedious part -
cleaning it all up. In the UV Editor use the Point,
Edge, and Face selection modes along with the
manipulation tools to pull and stretch the UVs until
they line up nicely, are straightened, and have
little or no distortion. Make use of the Weld
Vertices tool to attach adjacent faces as needed.
The time you spend here will really tell in the
final model. Even professional modelers sometimes
take shortcuts here - and it shows in their final
works (just freeze frame some of your favorite 3D
games and have a look.) My suggestion, take you time
and do it right - this is YOUR game after all!
Well, that's that. Now, select the Export Bitmap
icon and save an image of the UV map in your
preferred format - BMP or PNG are good ones
depending on which image editor you use to create
your bitmaps. Now, to splash on some paint!
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