Generating LODs


Creating the LODs is in some ways similar to optimizing the mesh. There are two principal stages:

  • First, look for areas that can be sacrificed, or in this case, what can't be seen when the camera is at that particular distance. For example, if the individual fingers are not visible when you zoom out, you can combine the fingers to create a mitten-type hand.

  • After you have removed any unnecessary detail, you can remove more polygons. Look for areas that create shallow angles and places that house unused polygons, just as you do in optimization. Continue to do this until you reach the polygon limit of the LOD you are creating.

Kila is currently made up from 4094 polygons. This will be the first LOD and the main model that will be used for close-ups. It's more than likely the next LOD will be the one mostly viewed in game. So let's create four more levels of detail for her at the following polygon counts: 3000, 1000, 500, and 150.

LOD 2: 3000 Polygons

Make sure the Kila_Pose.mb file is open. Before creating the second LOD, we must duplicate the current character's geometry. We only need one copy at this stage, because the LOD after this one will be based on this LOD 2's complete geometry.

1.

You should have all the pieces of the character in a group called Kila. Rename this to Kila4094.

2.

Duplicate this group, calling the new copy Kila3000.

3.

Create two new display layers (go to Layer > Create Layer in the Layer Editor), one for each separate version of the model. Call one Kila_4096 and the other Kila_3000, placing the appropriate group into each layer.

4.

Hide the original file (Kila4094) by turning off the layer's visibility, so you are only working with the duplicate.

5.

Position the model (by just moving the camera) as seen in Figure 10.12. She should more or less fill the screen; this will be the size of the full-resolution character.

Figure 10.12. The full-resolution model will be seen at this distance.


6.

Now dolly out until she is roughly half-size (Figure 10.13). This is approximately the distance at which this model will be viewed when in a game. When the main model is this far away from the camera, the game will switch to this LOD.

Figure 10.13. The distance of the next level of detail.


7.

Now that you have a basic distance to gauge your model on, begin rotating around her and see what you can initially sacrifice. At this distance you can still see quite a bit of detail; even her individual fingers are still visible. What you can do, though, is

  • Remove the highlights created for her eyes, and delete her eyelashes and her tongue. (If she does talk at this distance, you will not see it.)

  • Remove the single strand of hair from the front of her head, as well as the first inside layer of her hair. After doing this, you will need to tweak the remaining inner layers of hair to fill the gap that now exists.

That's about as much as you can remove at this stage, but she is still using 3878 polygons. Next we will go in and remove some areas of small detail in order to get closer to our 3000 limit for this LOD.

Hands

Although Kila's fingers are still visible at this level, they don't need to have much detail in them; it's sufficient if they merely "suggest" fingers. In designing the main hand, we included polygons around the joints so that the fingers would not pinch badly when bent. There is no need for these polygons at this distance, so we can remove them.

Reduce the fingers down to basic cubes like the ones seen in Figure 10.14, right. If you are merely merging vertices or collapsing edges, the UV information should stay intact.

Figure 10.14. Reduce the fingers down to basic cubes.


Reducing the fingers brings us down to 3236 polygons, not too far from our goal.

Sash and Jeans Legs

Let's now reduce some areas of detail in the sash and the jeans legs, which won't be missed at this distance. When creating the main model, we built creases on her hip to give the sash additional detail, and creases and folds in the jeans. This detail can now be removed.

1.

Begin by collapsing the main edges that create the overhang for the folds of the sash. These are highlighted in Figure 10.15a.

Figure 10.15. Remove the folds from her sash.


2.

Remove the final set of edges that made up the folds (Figure 10.15b).

3.

As you can see in Figure 10.15c, the UVs have been altered. So, open up the UV Texture Editor and fix the UVs using the main model (Kila_4096) as reference (Figure 10.15d).

4.

Remove the similar folds in the jeans at the back of her knees. Do this by collapsing the edges highlighted in Figure 10.16.

Figure 10.16. Collapse the folds at the back of her knees.


5.

Now focus on the folds at the base of her legs. Work your way around these, collapsing the majority of the edges until you have a more rudimentary-looking lower leg (Figure 10.17, right).

Figure 10.17. Reduce the folds in the lower part of the jeans legs.


With these reductions to the sash and jeans, our polygon count now stands at 2948, just under the limit. This is great newsit means we can move on and begin work on the next LOD.

Before you do, rename the group and the display layer to represent the new polygon count. So Kila3000 would become Kila2948, and Kila_3000 would be Kila_2948. This helps to inform others of the polygon count and keeps you up to date.

Figure 10.18 shows our second level of detail. You shouldn't see much of a difference in Kila's form at present, which is good because this model won't be too far away from the camera.

Figure 10.18. The second level of detail, up close.


LOD 3: 1000 Polygons

LOD 3 will be quite a dramatic step down because we will be able to remove a huge amount of polygons from areas where they are not seen at this distance.

1.

Create the base geometry to work on. Duplicate the previous LOD's group (Kila2948) and call the new copy Kila1000.

2.

Create a new display layer called Kila_1000, placing into it the Kila1000 group and its contents.

3.

Turn off the visibility for the layer called Kila_2948. This leaves you with just the new geometry to work on.

4.

As you did before, zoom out to about half the size of LOD 2 to get an idea of how the geometry will be viewed in a game. You can see this in Figure 10.19. From this distance, you can't see very much detail. Her facial features are lost, as are her fingers. It should be quite easy to reduce this version down to 1000 polygons.

Figure 10.19. Dolly out to about half the size of LOD 2.


NOTE

We could even go lower than 1000 for LOD 3. Just because we have a limit doesn't mean we must hit it exactly; we just can't go over it. If areas are not seen, then there is no use for them, so we may as well delete them.

5.

Let's first remove obvious things that can't be seen. This version of the model will not have any facial animation because you simply won't be able to see it, so you can remove the inner mouth, including the teeth, and weld her lips together.

6.

Remove her eyes and her ear; they won't be seen, either.

7.

Both inner layers of her hair can go, too. We can adjust the outer layer to compensate for this loss.

With these elements removed, we are down to 2692, so let's zoom in and begin reducing the main geometry.

Hair Reduction

Begin by working on her hair.

1.

Focus on her hair geometry by selecting it and pressing F.

2.

Select the edges shown in Figure 10.20 (left) and then collapse them (Figure 10.20, right).

Figure 10.20. Begin reducing the polygons in the hair.


3.

Delete the triangular faces at the very bottom of the hair and then weld the separate strips together, making the mesh solid.

4.

Optimize the hair further, removing polygons not only from the outside, but from the fringe of hair at the forehead (Figure 10.21, left).

Figure 10.21. Make the outer hair solid before extending it down.


5.

Extend the hair down to roughly match its original length on the higher-resolution model (Figure 10.21, right). It doesn't have to be exact; we can edit it more precisely in the next step.

6.

Because we have removed polygons, the overall shape of the hair will be less full. Make the LOD 2's display layer visible, turning the display type to Template. This will show the second LOD's geometry as a gray wireframe over the current model (Figure 10.22, left).

Figure 10.22. Use the wireframe of LOD 3 as a template to thicken the hair.


7.

You can now work on the hair, shaping it as seen in Figure 10.22, right, "thickening" it to match its previous look.

We will leave the hair as it is for now; this should be sufficiently reduced. Next we will trim down her face.

Face Reduction

We only really need to keep basic features in the face. Take another look at Figure 10.19; you can't see any major details.

1.

Focus in on the face. Feel free to hide the hair at this stage, to make working on the head easier. Then, as demonstrated in Figure 10.23 (top-right), weld the eyes closed.

Figure 10.23. Reduce the polygons in Kila's face.


2.

By now you should have a good grasp of polygonal modeling, so go ahead and work on the nose and then the lips (Figure 10.23, middle). Finally, work your way around the face, collapsing edges there until you have a basic face like the one in Figure 10.23, bottom-right.

NOTE

Remember to keep updating the UVs as you work, as well as checking the shape against the next-higher LOD.

Don't worry too much about deciding where to remove faces. Once you start collapsing edges, you will notice other areas that can be collapsed. They will stand out because the detail in that area does not match where you are currently working.

NOTE

The model is starting to look quite odd now, but remember that this version will only ever be seen from a distance. Keep zooming out as you work, to get a realistic idea of how she will look in a game.


You will probably have the urge to continue reducing polygons on her neck and the rest of her body, mainly because the head and body don't match anymore. But wait; we will look at the rest of the body later on. Next up are the hands.

Hand Reduction

The hands have far too much detail in them for this level. We no longer require separate fingers, for example, so we will convert them into flat, mitten-style hands as mentioned earlier.

1.

Begin by welding the fingers together as seen in Figure 10.24b, making sure you delete the inner faces afterward.

Figure 10.24. Adjust the fingers to get a mitten-type hand.


2.

Remove the finger ends, flattening out the end of the hand (Figure 10.24c).

3.

Work on the whole hand, reducing the overall detail, and remember to fix the UVs afterward.

You should now have a low-polygon mitten-type hand like the one shown in Figure 10.24d.

The reduced hands can now be used to guide optimization of the arms.

Limbs Reduction

Because we reduced the hands, triangles will have appeared at the wrist area (Figure 10.25). This is because the sections there no longer match up to the ones where the hands attach to the arms.

1.

On each arm, follow the triangles, and select the edges all the way up Kila's arm. You should end up with each alternate strip selected (Figure 10.26, left).

Figure 10.26. Reduce the divisions around the arm's axis.


2.

As you can see in Figure 10.26 (middle), collapsing these edges will reduce the arm from having ten divisions around the axis to five.

3.

Optimize each arm further (Figure 10.26, right), removing most of the detail we added to allow it to deform correctly. At this camera distance, you won't be able to tell whether the elbow and wrist look wrong as they bend.

4.

Now take a look at the legs. Remove most of the detail highlighted in Figure 10.27, left, following the polygons around to her buttocks. This will leave the legs in a more or less cylindrical shape.

Figure 10.27. Removing details from the legs leaves them with a basic cylindrical shape.


5.

We have a shallow angle on the thigh area. Select the edges shown in Figure 10.27, middle, and collapse them. The legs will look like those in Figure 10.27, right.

6.

In the crotch and buttock area, remove the polygons shown in Figure 10.28.

Figure 10.28. Remove polygons at the crotch and buttocks.


7.

Now repeat for the legs the steps used when you reduced the arms. Select the edges that make up every second vertical strip (Figure 10.29, left) and collapse them, reducing the divisions around the legs from ten to five.

Figure 10.29. Collapse every second vertical strip of polygons.


Figure 10.25. Triangles have appeared because the hand and arm no longer match.


The legs are now sufficiently reduced. Remember to use LOD 2 as a template to fill them out, since they will have thinned down when the edges were collapsed.

Torso Reduction

Compared to the rest of the model, the torso now looks out of character; it has too much detail. We need to remove some of this detail to bring it in line with the rest of her reduced geometry.

1.

Select the edges highlighted in Figure 10.30a, just at the base of her spine, and collapse them as shown in Figure 10.30b.

Figure 10.30. Work your way around the torso, removing any major details.


2.

There are quite a few areas to reduce on the torso; let's do them all at once. Follow Figure 10.30, selecting and collapsing the edges that are marked in white on both front (Figure 10.30c) and back (Figure 10.30e). After you make these changes, the torso should now resemble Figures 10.30d and 10.30f.

3.

Next, collapse the edges that form the overhang of her top (Figure 10.31).

Figure 10.31. Remove the overhang on her top.


4.

There are still quite a few polygons in her stomach that we don't need, so delete those (Figure 10.32).

Figure 10.32. Delete the extra edges in her stomach.


5.

Work your way along as shown in Figure 10.33 to collapse the edges on the breasts.

Figure 10.33. Remove detail on the breasts.


6.

Under the breasts, collapse the edges highlighted in Figure 10.34, left.

Figure 10.34. Collapse these edges under the breasts.


7.

On the chest and at the cleavage, remove all of the geometry highlighted in Figure 10.35, left.

Figure 10.35. Optimize the cleavage area.


8.

Finish off the chest area by working on its general shape (Figure 10.36). Remember to use LOD 2 as a guide.

Figure 10.36. The optimized chest area


NOTE

Don't forget the UVscorrect any incorrect areas as you progress.

9.

To complete your work in the torso area, quickly remove the division in her neck (Figure 10.37, left), making it a single flat area (Figure 10.37, right).

Figure 10.37. Remove the division in her neck.


Only the accessories are left to finish the reductions for LOD 3.

Belt and Shoe Reduction

Although we could just delete the belt, it is still slightly visible at this distance, so we'll take the time to reduce the number of polygons used to construct it. Then we'll work on the shoes.

1.

Remove the inside polygons on the belt, as well as the upper and lower edges (Figure 10.38a).

Figure 10.38. Belt reduction


2.

Collapse every other set of edges, removing every second polygon (Figure 10.38b and c).

3.

Adjust the shape of the belt so it does not cut through the character model (Figure 10.38d).

4.

To complete this LOD, reduce the shoes until they resemble Figure 10.39, right.

Figure 10.39. The optimized shoe


LOD 3 is finished. Look at the polygon count to make sure you are below the limit of 1000. Goodthe final count is 794, well under the limit. Rename both the geometry group and the display layer to reflect this number. Figure 10.40 shows the third level of detail; as you can see, Kila is now starting to look quite different from her original form.

Figure 10.40. LOD 3 up close


We are beginning to see some dramatic alterations to Kila's geometry. When we are finished with the next two LODs, she will be almost unrecognizable up close.

LOD 4: 500 Polygons

Figure 10.41 shows the next LOD's distance from the camera. As you can see, we are getting quite far from our character and can no longer see any details. All we can see is her basic shape.

1.

Just as you did before, duplicate the previous LOD's group and rename it to Kila500, placing it into a new display layer called Kila_500.

2.

Start by deleting her belt, which is no longer visible at this distance.

3.

On the hands, remove the thumb before reducing both hands right down to their basic shapes (Figure 10.42).

Figure 10.42. Reduce the hands to basic shapes.


4.

The arms currently have five divisions around the axis, so we can reduce them down to four (Figure 10.43). Select the edges at the very front of the arm, and collapse them.

Figure 10.43. Optimize the arms down to basic shapes.


5.

Now you can remove the polygons that add shape to the arms, shown in Figure 10.43, middle. Again, these won't be visible when the camera is at this distance, so it's safe to remove them.

6.

Moving on to the hair now, this can be reduced to a basic box shape like the one in Figure 10.44, right. You can even remove all of the internal geometry, if any still exists.

Figure 10.44. Reduce the hair geometry down to a basic box shape.


7.

Reduce the face as demonstrated in Figure 10.45, removing the details for her eyes, nose, and lips and leaving her face more or less flat.

Figure 10.45. Remove details from the face.


8.

The legs can be reduced in the same way as you did the arms. Select the edges at the front and collapse them, reducing the divisions around the legs from five to four (Figure 10.46).

Figure 10.46. Reduce the divisions around the legs.


9.

When the legs are reduced, you will notice areas around the crotch and waist that can be optimized. At this level, polygons to aid deformation are not needed, so select and collapse the edges highlighted in Figure 10.47 top-left and top-right.

Figure 10.47. Optimize the waist and crotch.


10.

Now you've come to the torso. You only need the basic shape to represent the character, so there are quite a few areas you can reduce here. Remove the edges shown in Figure 10.48 top-left and bottom-left, giving you the torso seen in the top-right and bottom-right of Figure 10.48. After removing the polygons, you will need to fine-tune the shape slightly.

Figure 10.48. Remove most of the detail from her torso, leaving the basic shape intact.


11.

Finally, work on the shoe, reducing it down to the basic shape seen in Figure 10.49, right.

Figure 10.49. You only need a very fundamental shape for the shoe.


Figure 10.41. LOD 4's distance from the camera


LOD 4 is now complete and you can see it in Figure 10.50.

Figure 10.50. LOD 4 up close


Checking the polygon count shows we are down to 309another successful reduction. Rename the group and display layer to reflect the correct polygon count, and move on to create the final level of detail

LOD 5: 150 Polygons

We are now at the final level of detail, the most basic version of our character. Figure 10.51 shows the distance at which this version will be activated; not much at all can be seen. We can just about make out arms, legs, and a torso, so these are the areas we will concentrate on.

1.

Create a copy of the LOD 4, renaming it to Kila150.

2.

Place this copy into a new display layer called Kila_150, and hide the display layer of the previous version.

3.

Delete the hair and shoes.

4.

You only need a vague representation of arms, so completely remove the hands, merging the end of each arm into a single vertex (Figure 10.52).

Figure 10.52. Remove the hands and merge the ends of the limbs.


5.

You won't see the face at all at this distance, but you do need something to represent her head. Delete the faces under her chin, and then work on the head until it's a basic flat cube like the one in Figure 10.53. Not only will this use fewer polygons, but it will work well from a distance.

Figure 10.53. Reduce the head down to nothing but a basic cube shape.


6.

Remove any extra polygons on the legs that add to their shape. All you need at this stage are very basic cube shapes (Figure 10.54).

Figure 10.54. Leave just two basic cubes for the legs.


7.

Finally, there's no need for details on her torso, either. You just want a basic shape, so remove the areas highlighted in Figure 10.55 top-left and bottom-left to make them like Figure 10.55 top-right and bottom-right.

Figure 10.55. Optimize the torso area.


Figure 10.51. LOD 5's distance from the camera


Our final level of detail weighs in at 120 polygons. She's not much to look at (Figure 10.56), but you have to remember she will never be seen this close in the game. Rename the final group and display layer to represent the polygon count (Kila_120) and save the file as Kila_LOD_Prep.mb.

Figure 10.56. LOD 5 up close


Our LOD model for Kila is complete, but will it work? Once we have completed the reductions on Grae, we will test both characters' LODs to see how they will look in a game when the characters move away from the camera.



    Game Character Development with Maya
    Game Character Development with Maya
    ISBN: 073571438X
    EAN: 2147483647
    Year: 2004
    Pages: 169
    Authors: Antony Ward

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