| Creating
eyeballs in Softimage XSI
Depending on the style of animation you wish to create, a sphere with a texture map can work perfectly well in portraying an eyeball, especially if you are going for a cartoon look. However, I was quite interested in creating an eye which had a lot more depth.......the kind of eyeballs you might expect in 'Monsters Inc' and 'Ice Age'. When recreating such an eye, we notice that it shares alot of similarities with a real eye: they look wet, have subdued reflections and are able to catch sharp highlights in certain areas, which gives the illusion that the eye has depth. In this tutorial we are going to look at four stages associated when creating such an eye in XSI; the geometry, the shader, lighting and rigging the eye so that we can control the size of pupil and eyeball. Lets start with the geometry first. The best way to fake the eye is to break the eyeball into it's basic components and then model each one separately. We can then group each mesh together so that it resembles the eye. Normally the eye can be broken down into 4 components:
The Pupil is a simple flat black 2d circle that sits in the iris. The Cornea is
a key component to the eye. It allows us to catch sharp highlights
and it gives the eye depth. Actually the combination of the cornea,
iris and pupil are what give the appearance of depth but without
the cornea this eye would look flat. The cornea is transparent and
has a light reflection map. Its main purpose is to catch a sharp
highlight However I'm going to cheat. The pupil can be left out as we are going to use shape animation on the Iris to open and close, allowing us to see inside the eyeball....which will be an inner sphere with a constant black material. Don't worry, it will all make sense later on in the tutorial. All u need to know is that for now, we are going to model the 4 components below.
Note : Don't freeze any of the objects that we create (and make sure you are not in 'Immed' mode........as we want to keep some parts of the history and certain operators, the reason will become apparent as you work through the tutorial.......... First of all
grab a polygon sphere Get>Primitive>Polygon mesh>sphere
and name it 'white_eye' and rotate it locally in x
by -90 degrees (u can use a surface mesh if u prefer too). Up the
subdivision in the geometry property page to 12 for both u and v.
Then go toTransform>Freeze all transforms to reset
the rotations to 0. Select the sphere named 'Eye_white' and press return to open it's property page. If it doesn't open then go toselection and click on the polygon general property icon
In the property page that opens, change the start angle in V to 20 , so that we have a hole in the front of the sphere.
Unhide the sphere named 'cornea'. The corneas sits in the front of the eye, it's transparent and allows us to catch the highlight from any lightsources. Depending on whether you are using polygon or NURBS object, then the setting may be different.....just use values that look correct. I used a polygon object and increased geometry approximation at render time to get the look I want. Therefore if you used a polygon object, I found that after Opening the corneas property page, changing it's Subdivisions in U to 12 and V to 1, and then the End V to 20 was quite adequate. The cornea should fit tightly over the sphere called 'White_eye'. However the cornea should bulge slightly in the front as shown in picture below. Therefore grab the front points or polygons and move them slightly forward.
Some
thoughts on the Iris and Pupil
The Iris can be tackled in two ways. In both methods however, the Iris will also act as our pupil. The first method is a little long winded, however, could be useful if you wanted to create different pupil shapes....i.e. Like a cat or monster. 1) The Shape Key Way This method can only be used with Polygon meshes, as it requires us to delete faces. Unhide the Iris sphere and in it's property page make the subdivisions in U and V 12 and 1 respectively. The Iris bends inwards, so tag some points and move them backwards. Then go into raycast mode (u), select the inner polygons and delete them.......this hole is going to be our pupil.
Now duplicate the Iris object twice and move them to one side and name them 'default_shape' and 'big_iris_shape'. In order to give the illusion that the pupil is getting bigger and smaller, we need the original mesh's hole to increase/decrease in size, this is why we are going create shape targets for the 'iris' mesh to blend between in the animation mixer. Select the 'big_iris_shape' mesh and tag the points around the hole. Scale them using the transform tool, so that the hole gets bigger.
Select the original 'Iris' mesh and then in the Animation panel go to Deform>Shape>Select shape key and choose the meshes 'default_shape' and 'big_iris_shape'. Right click to end picking. We have now created the shape targets. To make them work we need to lay the shape clips on a shape track in the Animation mixer. From any of the viewports select Animation Mixer, or press alt+0 to bring up floating window. Select the original Iris mesh and update the mixer. You should see two green Action tracks, we want two shape tracks, so right click in the tracks and select Add Track>Shape or press shift+s. Two blue tracks will appear. To insert the shape clips, right click once again on the shape tacks and select Insert source, another menu will appear with the names of the shape clips that we created earlier. Place each one on separate track as shown below.
Resize the clips length so that it extends for the entire animation's length. You should now find that changing the blending weight on the track with the 'big_iris_shape' clip will make the iris mesh located on the eyeball change shape.
There is currently a problem though. Have you noticed that when blending between the shapes, the Iris is not morphing into the exact shape we had anticipated....instead the shape being created is more subdued. This is because the mixer is currently averaging between the two shape targets 'default_shape' and 'big_iris_shape'. We want the mixer to be in additive mode. With additive mixing, the shapes are literally added together to create a composite result. With additive mixing, you can exaggerate shapes by setting values higher than 1. In order for the mixer to deal with shape clips in a additive manner, we need to turn off 'Normalize' in the Shape Mixer Properties. Go to Mix>Shape Animation Properties in the Animation mixer window and turn off Normalize.
Now when we blend the weights, the iris shape should update correctly. One more thing to note: should you want the pupil to ever become as small as a pinhole, then we can amend the mesh 'default_shape' (the one that is a shape target) so that the hole is smaller (tag the points near the hole and scale them down). As there is a relationship between this mesh and the original iris mesh (because of the stored shape key information), the new meshes shape will propagate to the original 'iris' mesh. 2) The Property Page Method This method is a lot easier, bit not as flexible as the shape animation method. For a start, we won't be able to have different Iris/pupil shapes, however, because we are going to be using a standard property page that is associated with every object created within XSI, we will have no operators to slow our computers down. Whilst the NURBS 'Iris' mesh is sected, click on selection in the Transformation panel. Typically under each object, there is a subnode named Polygon Mesh, NURBS Surface Mesh etc. which contains parameters that allow us to change the properties of an object.
Because we have not frozen any of the meshes (I told u it would come in useful!) we can use this Property page to make further amendment to the mesh, and animate them. Because we are using a NURBS mesh, we won't be able to delete the points to create the hole. You can however set the subdivisions to 12 and 2 in U and V, and use the Start V in the Extent (Angles) sub heading to create the hole! Don't slide this value higher than the End V, otherwise the mesh will twist back on its self. The Constant shader The last component of the eye is another sphere. This sphere is given a constant black shader and scaled to be slightly smaller than the 'white_eye' sphere. It is then placed inside the 'white_eye' mesh, so that when we look at the Iris mesh, the hole allows us to see the black sphere behind it, or as I like to think of it, the Pupil! Because we don't have a pupil mesh, we don't have to worry about pupil resizing correctly when we want it too..............it's all taken care of by the Iris!
Putting it all together As mentioned before, in XSI there is an attribute that is associated with every primitive object that is created, and we can use this to tie together all our spheres geometry, so we can animate the Iris/pupil sizes, with just one slider. Once again we are going to use the subnode found under each mesh to amend the the Start and End U and V's found in the Extent (Angles) area. We know that all of the components we have created for the need to be amended as one. We are now going to place a simple expression on the Start and End UV so that they are all linked....therefore when one slider is moved, all the others move as well.
Select the 'White_eye' mesh, and open its property page by pressing return. Lock this window. Notice that when we increase the value of the Start V slider, the hole on the mesh appears to get bigger. Now open the 'Iris' mesh's property page. Lock this window too. Notice again that inceasing the value of the End V slider, the Iris mesh grows to create a sphere. (note, if you rotaed the sphere in + 90 degrees at the start of the tutorial, this will be the other way round!). Therefore, in effect ,it will plug the hole created when appending the 'white_eye Start V slider. To create the link, right click on the Iris's End V green nodule, and select Set Expression.
Click to enlarge In the expression editor that pops up, type:
We have now stated that the Iris's End V is equal to the white_eyes Start V. Now when you move white eyes Start V slider the iris should automatically follow. Link the 'inner_constant_colour' and 'cornea' sphere in the same way so that it too changes shape at the same time as the other components.
Polygons have been hidden on the 'White_eye'
mesh The only thing
to do now in terms of the eyes construction is to amend the Iris
mesh, so that when the Start V gets bigger, the Iris
is still bent inwards. At the moment is starts to straighten, which
will ruin the effect of depth once we apply shaders to the eye.
This can be done using a another blend shape, which bends further
inwards as V increases. |
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