View source for Doc talk:Cut-out Animation using Group Transformation Widget

   Rewrite preparation for 0.65

== Grouping the parts ==
After importing the png images they are automatically placed in a switch layer. We have to turn them into normal groups first. Also make sure that your groups have the same hierarchy as in picture (a). So the pivotRightarm layer has to be on top, followed by the pivotHip layer, etc.

Setting pivot points.
We are going to animate the parts of our character by using the Group Transformation Widget. If we click on a group in the Layers Panel then we can see the Group Transformation Widget on the canvas picture(b). Click here for more information about the Group Transformation Widget. To rotate the parts of our character we have to set a pivotpoint for each of the part. The Group transformation Widget will rotate the part using the pivotpoint as the origin for the rotation. We will start with the hip. Select the pivotHip group in the Layers Panel. Press space and drag the bottom left green handle of the Transformation Widget to the position of the hip where we want have our pivotpoint picture(c). Do the same for all the others parts of the character. Just select the group in the Layers Panel, press space and drag the bottom left green handle of the corresponding Group Transformation Widget to the correct position. When finished control select all layers in the Layers Panel and your canvas should look like picture(d). To rotate a part just select its corresponding group in the Layers Panel and drag the blue (rotation) handle of the group transformation widge and the part should rotate around its pivotpoint. The parts are not connected yet. When we rotate the hip then the body, head and arms should rotate alongside it and we still have to assemble the pieces so that we get one cohesive character. 

== Building limb hierarchy ==
We are now going to connect the body, the head and the arms to the hip so that when we rotate the hip all the other parts rotate alongside with it. Select the pivotHip group in the Layers Panel and then go to the Parameters Panel (e)and open up the Group Transformation Widget information by clicking the little plus in front of it (e1). Right click on Offset (e2) and choose export (e3) and name the exported value pivotHip (e4). Also right click on Angle (e5), choose export and name the exported value angleHip (e6). When we go to the Library panel (f) and click on the little plus sign (f1) in front of ValueBase Nodes then we see our two exported values (f2) and (f3). 
First we will connect the right arm to the hip. Select the pivotRightarm group in the Layers Panel, right click and choose group. Name the group rightArm. Now go to the library panel and select the pivotHip ValueBase Node (f2). Go to the Parameters Panel (g), open the Group Transformation widget information by clicking the little plus in front of it (g1)and right click on Offset (g2)and choose connect (g3). The arm will move slightly downwards but we will correct that later when we assemble the character. Now go to the library panel again and select the angleHip ValueBase Node. With the rightArm group still selected go to the Parameters Panel, open up the Group Transformation Widget information by clicking the little plus in front of it (it's probably still open) and right click on Angle and choose export. We now have a group called rightArm that is connected to the hips origin and angle and a subgroup pivotRightarm that rotates around its own pivot point. When we select the pivotHip group in the Layers Panel and rotate it with the blue handle of the group transformation widget the the hip will rotate and the right arm wil rotate alongside with it. When we select the pivotRightarm group and rotate its blue handle then the arm will rotate independently from the hip. After you tried both rotations just press undo untill you get to the original layout. Now we will have to do the same for the body, the head and the left arm. Select the pivotBody group in the layers panel, right click and choose group and name the group Body. Select the new Body group and connect its origin and angle of its Group Transformation Widget to the corresponding exported ValueBase Nodes. Don't forget to select the right ValueBase Node in the library Panel before you connect them. 

== Assemble the character ==
Now that all parts are connected it is time to assemble our character, because it kind of looks messy at the moment. 
Select the pivotBody group in the layers panel and drag the bottom left green handle (do not press space!) untill the body is in the right place above the hip. Do the same for the pivotHead group, the pivotLeftarm group, the pivotRightarm group, the pivotRightleg group and the pivotLeftleg group. When finished our character should look like this.(h). We have to be able to move the entire character including the legs so select all groups in the Layers Panel, right click and choose group and call the group Character. When we select the group Character we can use its group transformation widget to transform the entire character and all the connection in the group will stay intact.

== Tip == 
Elbow and wrist joints or knee and ankle joints do not have to be connected to the exported ValueBase Nodes of the pivotHip group because it is enough that you put them in a subgroup and they will rotate properly.