Posted on 2010-10-01 15:20:32

Rigging a Book Part 2

For this part of this akward book rigging tutorial, we'll deal with the stack of pages that's left behind when you turn pages. I'm talkin about the bulk that bends when the book is bent.

If you noticed, whenever the book opens, there are two stacks left on either side. We can't call these pages cuz we've already used the term to refer to the lose leaves that sort of flap when you turn pages. The first part of this tutorial talks about the initial phase of rigging those lose leaves. This tutorial will talk about the stack left behind.

It's fairly simple to rig this stack, if the book is to remain close the whole time. But once the book opens, the stack remains rectangular from some views, but from the dominant view of the video you get this cross-section that's unique to books. It starts out like a fan and toward the end it's a skewed rectangle. The middle part is a gradual blend of the shape from fan to skewed rectangle.

wegetthis1.

Achieving this shape in Maya (or I presume any 3d Program with the right amount of tools) is fairly simple. First, let's talk about the fan shape.

fan

To make a mesh, cubical in nature in the typical way books are, bend in the same way the illustration above depicts, you'll need dual quaternion skinning. Since Maya 2011, dual quaternion has been added as an alternative method of deforming skinClusters. What this means is we don't lose volume when we have joints of conflicting rotations influencing the same vertexes.

Consider the following scenario. Have a block of mesh with a moderate number of subdivisions sit on the grid. On two opposing bottom corners of the mesh, have one joint each. Have the weights of the joints on the mesh look like a black and white gradient (linear) from one side to the other (horizontal, if your joints are lined up horizontally). Then rotate one joint. If you don't have dual quaternion, your mesh will form a sort of fan but skewed in the same direction you are rotating to. If you have dual quaternion, you'll have a perfect fan.

In the rig I made, I applied this concept on a lattice deforming a mesh instead of directly applying it to the mesh.

fan lattice

The two spots represent two joints. The cage on the left is the lattice when the book is closed. The cage on the right is the lattice when the book is open. I'll have our actual mesh (two of them) sit on one corner (one corner each) and let it scale from that corner, on cue.

fan lattice with contents

The color red represent the mesh state when it's thin. The color yellow stands in for the mesh when it's stretched. If you saw the video of the book rig, you'll remember the part when I was adjusting the page index. This controls the thickness of the mesh inside the lattice that spreads into a fan when the book is open exactly the same way a mesh represented by red becomes a mesh represented by yellow in the illustration. We'll leave this for a while.

The next thing we need to accomplish is another shape that would give us the "skewed rectangle" effect common in books' edges. This is actually simpler achieved than you'd think. It's a simple blendshape activated either by the rotation of the stack or the distance of one corner of the book to the other.

blendshape

You'd also want to give this shape a scale control similar to the what we gave the first ("fan") shape that controls thickness, just to keep them matched.

The last step to controlling the stack is to have yet another copy of the block shaped mesh. This will receive a blendshape that has two targets, and yes you guessed it, we'll make this shape morph into both the shapes we just created earlier: 1)the fan looking thing and 2) the skewed rectangle. To make this blendshape work properly, we'll need to set up the mode of the blendshape to world instead of local. We'll turn on both targets. Then we'll use the edit blendshapes tool to make the fan shape target influence only the lower part of the mesh and the skewed shape target influence only the upper part. And viola.

Next part of this tutorial, we'll try to finish this book rig.

happisis chan
2010-10-05 06:46:00

this is cool!

ric
2010-10-23 04:09:26

awesome

justin
2011-01-28 07:51:27

Hey David the rig looks great! Any chance you'll post it on your site?

animo
2011-02-03 09:11:35

hello, thank you for your tutorial, could you plesa finich the third part please

animo
2011-02-03 09:12:37

hello, thank you for your tutorial, could you please finish the third part please. It would be awesome cuz such there is no analog tut on rigging the book. Nice work!

ayhan baruch
2011-04-11 17:27:44

Thanks for this.

wangyan
2012-05-28 02:09:47

Hi~the book system is amazing,I learned a lot from your scense that you puted on your website.but I still couldn't understand several detials on it.would you please make a video tutorial or sometings step by step when you are free,I'll keep my eyes on your blog.

dhia.designer
2017-07-25 09:34:58.231940

Thanks for this.