In Ziva VFX, there are two options for connecting tissues and bones to one and other – Fixed and Sliding Attachments. Both are effective but significantly different, so it’s important to consider the effect you’re wanting to achieve in your simulation.

Sliding Attachments allow you to make any Ziva object (tissue, bone, etc.) slide along the surface of another object while preserving their separation distance. The object where attachment vertices are located and fixed to is the “Source Object” while the object that slides along the Source Object surface is the “Target Object”. The order in which you select your objects will dictate which is the Source and which is the Target. We've included a few examples to help illustrate the relationship at the bottom of this page.

• First Select = Source Object
• Shift+Select = Target Object
  
  

How to Make a Sliding Attachment

To create a Sliding Attachment, you can self-select the vertices that you wish to attach or use our built-in Proximity Tools to automatically discover the closest regions of contact between your tissue/muscle/bone objects. We recommend following these steps to create a Sliding Attachment between two muscle segments:

1. Select your Ziva Bone or other source object
2. Shift+select the tissue or bone that you wish to attach 
3. Go to the Ziva Menu —>  “Proximity Tools” —> “Select Vertices”
   This tool will help you select all of the vertices within a limited proximity on the two objects. You can alter the radius, but often default 0.2500 will suffice. 
4. With the selected vertices, go to Zive Menu —>  “Add Simulation Component” —> “Add Attachment”
   Immediately, you attachment will appear with red markers. However, the red markers indicate a FIXED attachment, not the Sliding Attachment. 
5. Go to the Attachment window on the right-hand side and change the “Mode” from “Fixed” to “Sliding”.

Your attachment markers will go from red (fixed) to blue (sliding). These coloured markers will help you identify where your attachments are and how they differ. 

Much like Fixed Attachments, you can change the strength of your Sliding Attachments by changing the “Stiffness” and “Stiffness Exponent” parameters. Since many users want sliding attachments to be in constant contact, they often attempt increasing their Stiffness Exp to extreme large quantities. We highly recommend against using stiffness strengths that are unrealistic or inorganic as it can cause scene instability. Try testing your attachment results with the default 1x10^8 and reducing or increasing the Stiffness Exponent as needed. 

Source–Target Relationship Example

A good reference for the Source–Target relationship is the Slithering Snake & Table example. The bottom surface of the snake must slide and slither along the surface of the table. So, since the points of contact of the snake does not change, nor does it's contact with the table, the snake must be the “Source” and the table surface must be the target “Target”. 

You can apply this very logic to an anatomical example, so, if you were to have a muscles and a skin with a sliding attachments, you’d need the muscles to be the Source objects since the skin must slide along the muscle surface and web across the muscle segments.

In the video tutorial above, Ziva Technical Director Andy van Straten illustrated the relationship using a drawn diagram and provides more Source-Target relationship examples. If you'd like the continue learning about ZIVA VFX Sliding attachments, we also recommend visiting the ZIVA VFX Documentation Attachments section.