Portal de Periódicos da CAPES

Interactive tools to support animation tasks.

1986; Complutense University of Madrid; Linguagem: Inglês

1988-2548

Frederic I. Parke,

3D Surveying and Cultural Heritage

Interactive tools have long been important fundamental components of computer animation systems. Interactive tools in the form of electronic paint systems, cel painting systems, and in-betweening systems are major components of two-dimensional character animation systems. Major interactive components of three-dimensional animation systems include motion design and motion previewing systems as well as geometric modeling systems.Two-dimensional animation systems have as design criteria the application of computer systems and technology to increase productivity and cost effectiveness while at the same time utilizing the skill and talent of non-computer oriented animation production staffs. One of the most effective ways to meet both criteria is through the use of highly interactive system components.One of the original motivations for the development of electronic paint systems was to support the task of creating background paintings for computer animation. Additional applications of paint systems to animation include color selection and matching, storyboard development, and character design.One of the major tasks in two-dimensional animation is the creation of very large numbers of line drawings. These drawings are of the characters, portions of characters, and other objects contributing to the animation action. In conventional systems, these are created by a hierarchy of animation artists using pencil and paper techniques. A relatively few “key” frame drawings are drawn by lead animators with the remainder of the drawings done by junior animators and inbetweeners. In computer based systems considerable economy can be realized by using algorithms to generate the in-between drawings based on key frame drawings created interactively by the lead animators.Once these many drawings are created, they must be colored. In conventional systems this is done by transferring the drawings to acetate sheets which are colored on the reverse surface with specially formulated paints. In computer based systems, interactive workstations based on specially modified paint systems are used. These workstations usually include the capability to automatically fill in similar areas of drawing sequences. These interactive cel painting stations can greatly increase productivity over conventional techniques.These interactive workstations usually use tablets and menus to support artist interaction. The paint and cel painting systems use raster displays driven from frame buffers. The in-betweening systems make use of high performance two-dimensional calligraphic vector displays.In current three-dimensional animation systems, interaction is used in two major task areas; motion design and geometric modeling. Because the rendering processes commonly used in such systems are so computationally intensive there is great motivation for being able to carefully design and preview the various motions before actually rendering the finished frames. As a result, most serious three-dimensional animation systems include interactive workstations specifically designed to allow animators to set-up and preview the animation in real-time. Such systems are built around very high performance display systems which support three-dimensional coordinate system transformation and high speed vector drawing. This high performance is needed to allow the three-dimensional object positions to be updated in real-time at video or film frame rates. The graphic display systems that have been used include the Evans & Sutherland MPS and PS-300 as well as the Silicon Graphics Iris.Examples of such motion design systems include the BBOP [1,2,3] system originally developed by Garland Stern at NYIT and the TWIXT [4] system developed by Julian Gomez at Ohio State. The BBOP system is currently in its third generation. It has been supported on a succession of hardware systems including the E&S PS1, PS2, and MPS systems. Since the E&S MPS systems are no longer being manufactured, the BBOP system has been ported to the PS-300 family and a port to the Trillium 1100 system is expected.These motion control systems are basically “key pose” oriented. The animator can interactively position or pose the animated objects at specified key frames. Software then automatically creates the object positions for all the intermediate frames based on the key poses specified by the animator. The objects or characters being animated typically consist of a hierarchically structured tree of sub-objects. Each node of these structures corresponds to a coordinate system transformation. By manipulating the transformations at each node, the animator can pose the objects or characters as desired. The intermediate frames are created by interpolating the key frame node transformations. In addition to node transformations, the animator can control the camera parameters such as viewing position path and field of view.Interaction with this system is through tablet, joystick, and “joyswitch.” The joyswitch allows the animator to select the current transformation node by moving up, down, right, or left in the tree structure. The three-axis joystick allows interactive control of node rotation, scaling, and translation. The tablet provides an additional interactive input mechanism. In addition, the system allows all actions to be specified from the keyboard if desired.The other major use of interaction in three-dimensional animation is to support the creation of object models. To create the synthetic images and to drive the motion control systems, geometric models of the various objects and sub-objects must be specified. Without interactive modeling systems this can be a very labor intensive and time consuming task. The goal of interactive modeling systems is to support the rapid development of complex object descriptions.The current modeling system in use at NYIT is supported on both E&S MPS and PS-300 systems. The original work was done by Pat Hanrahan [5]. This has since been expanded into a framework for interactive modeling packages. The framework provides an interaction core which provides windowing, menuing, and interactive device handling support. A number of specific modeling functions have been developed which are supported by this framework. This framework makes developing a new modeling function relatively easy.To date, interactive three-dimensional motion specification and geometric modeling systems have utilized high performance vector display systems. This is simply because these have been the only reasonable systems available. High performance, full color, shaded systems have been in existence for some time in the form of real-time visual simulators. But until recently these have all been much too expensive for regular use in animation systems. Recently, however, relatively inexpensive but still high performance full color shaded systems such as the Trillium 1100 have become available. The Trillium system provides real-time performance as good or better than previous vector systems but with the advantage of full color shaded images and a movable light source. Major software development efforts are underway to port motion control and modelling software to this system.In addition to rapid vector generation and/or polygon shading the major hardware feature utilized by current interactive workstations is rapid coordinate transformation hardware. Interactive modeling systems could greatly benefit from rapid hardware to support a much wider range of geometric operations such as the computation of planar equations, surface intersections, spatial set operations, etc.The current hardware systems are well suited for articulated structures of rigid bodies. However, they currently provide little support for the modeling or motion specification of objects with deformable surfaces. The incorporation of real-time interpolation hardware would be a great help in dealing with “organic” structures such as the human form.