ADD Droopiness to a singlevolume character In Ziva
While ZIVA VFX can be primarily used to create photorealistic characters driven by physics-embedded anatomy, it is also useful in producing dynamic feature animation characters that might not necessarily have complex anatomy. This example shows you how to increase the visible ‘droopiness’ and ‘weight’ of a specific body region on a single-volume character by altering its material parameters.
how objects IN ZIVA Work 01
Here, we have a cartoon elephant that consists of a single, uniform volume and a basic biped rig. Unlike a more complex anatomical character which would be comprised of numerous muscles, bones and cloth layers, this cartoon elephant is a single solid object.
All objects in ZIVA VFX have material properties that correspond to real-world physical properties such as density and elasticity. These properties can be set to a fixed value throughout the object, or can be made to vary across the object. For our elephant, this means that we have the flexibility to easily make part of its body appear heavier or jigglier.
control The Mesh 02
To achieve this, first select the character mesh by clicking on any point of the character. The tet mesh will appear as thin grey triangles (tets). These control the resolution at which the material can deform. From here, go to the Ziva menu on the top menu bar in Maya and then select the Material Layer option. This will automatically add a material layer to the character.
choose MATERIALS 03
Next, right-click on any area of your character and the Materials menu will appear. Here, hover over Paint and select zmaterials. In the zmaterials submenu, you can pick from the various material layers that you have created. For the purpose of this example, there is only one option available to us: ‘zmaterial1_weights’. However, if you had previously created multiple material types, then they would all be selectable here and would be numbered accordingly.
In ZIVA, a material refers to the physical properties of a tissue or cloth. This includes simple properties like density, which affects mass and inertia. It also includes some more complicated material properties, such as the model of the relationship between strain (essentially displacement) and stress (essentially elastic forces).
APPLY MATERIALS 04
Upon clicking ‘zmaterial1_weights’, a paintbrush cursor and menu will appear. This tool enables us to easily define the areas of the character mesh where we wish to apply the material parameter changes (white paint) or, alternatively, select the areas we wish to leave unaffected (black paint). The intuitive paintbrush tool is used throughout for fast, effective section selecting.
In this example, only the bottom portion of the elephant has been painted, since we would like to increase the weight and jiggliness of the belly region only. We’ve also selected the Flood option located on the paintbrush menu, on the left-hand side. This function will automatically smooth out the otherwise rough painting we just completed. This creates a more organic, natural transition between the painted and not-painted areas.
MATERIAL QUALITIES 05
Once you’ve finished painting, select your new material in the channel box. This will prompt a list of material parameter input fields to appear. To show a significant material change around the lower half of the elephant, we can reduce the Young’s Modulus to 10^2 and lower the Volume Conservation to 10^6.
The Young’s Modulus parameter controls the ‘stiffness’ of the material. We suggest using the standard real-world stiffness values for muscle, tendon, fat, etc. provided in the ZIVA VFX Documentation. Volume Conservation, on the other hand, controls the liquidity and compression resistance of a material. Typically, the numeric value for Volume Conservation is set to be 10^2 – 10^7 greater than that of Young’s Modulus. With a sufficient level of volume conservation or compression resistance in ZIVA VFX, you can even achieve a soft, goop-like behaviour. In this example, though, we will set the stiffness and volume conservation values to be similar to gelatin.
See The RESULTS 06
Once animated, the results of the new material settings are very distinguishable. By painting only the lower portion of the elephant and modifying the material parameters in the region, we are able to visibly increase the droopiness of the character’s lower stomach region while still preserving its volume.
Adding profound secondary dynamics, even on simple feature animations, is easily achievable with ZIVA VFX. Not only can this function be applied to single-volume characters made with the Maya plugin, but characters created outside ZIVA can benefit from the robust physics simulations too.