James McCann

Responsive characters from motion fragments

In game environments, animated character motion must rapidly adapt to changes in player input - for example, if a directional signal from the players gamepad is not incorporated into the characters trajectory immediately, the character may blithely run off a ledge. Traditional schemes for data-driven character animation lack the split-second reactivity required for this direct control; while they can be made to work, motion artifacts will result. We describe an on-line character animation controller that assembles a motion stream from short motion fragments, choosing each fragment based on current player input and the previous fragment. By adding a simple model of player behavior we are able to improve an existing reinforcement learning method for precalculating good fragment choices. We demonstrate the efficacy of our model by comparing the animation selected by our new controller to that selected by existing methods and to the optimal selection, given knowledge of the entire path. This comparison is performed over real-world data collected from a game prototype. Finally, we provide results indicating that occasional low-quality transitions between motion segments are crucial to high-quality on-line motion generation; this is an important result for others crafting animation systems for directly-controlled characters, as it argues against the common practice of transition thresholding.

Real-time gradient-domain painting

We present an image editing program which allows artists to paint in the gradient domain with real-time feedback on megapixel-sized images. Along with a pedestrian, though powerful, gradient-painting brush and gradient-clone tool, we introduce an edge brush designed for edge selection and replay. These brushes, coupled with special blending modes, allow users to accomplish global lighting and contrast adjustments using only local image manipulations --- e.g. strengthening a given edge or removing a shadow boundary. Such operations would be tedious in a conventional intensity-based paint program and hard for users to get right in the gradient domain without real-time feedback. The core of our paint program is a simple-to-implement GPU multigrid method which allows integration of megapixel-sized full-color gradient fields at over 20 frames per second on modest hardware. By way of evaluation, we present example images produced with our program and characterize the iteration time and convergence rate of our integration method.

DynaMMo: mining and summarization of coevolving sequences with missing values

Given multiple time sequences with missing values, we propose DynaMMo which summarizes, compresses, and finds latent variables. The idea is to discover hidden variables and learn their dynamics, making our algorithm able to function even when there are missing values. We performed experiments on both real and synthetic datasets spanning several megabytes, including motion capture sequences and chlorine levels in drinking water. We show that our proposed DynaMMo method (a) can successfully learn the latent variables and their evolution; (b) can provide high compression for little loss of reconstruction accuracy; (c) can extract compact but powerful features for segmentation, interpretation, and forecasting; (d) has complexity linear on the duration of sequences.

Local layering

In a conventional 2d painting or compositing program, graphical objects are stacked in a user-specified global order, as if each were printed on an image-sized sheet of transparent film. In this paper we show how to relax this restriction so that users can make stacking decisions on a per-overlap basis, as if the layers were pictures cut from a magazine. This allows for complex and visually exciting overlapping patterns, without painstaking layer-splitting, depth-value painting, region coloring, or mask-drawing. Instead, users are presented with a layers dialog which acts locally. Behind the scenes, we divide the image into overlap regions and track the ordering of layers in each region. We formalize this structure as a graph of stacking lists, define the set of orderings where layers do not interpenetrate as consistent, and prove that our local stacking operators are both correct and sufficient to reach any consistent stacking. We also provide a method for updating the local stacking when objects change shape or position due to user editing - this scheme prevents layer updates from producing undesired intersections. Our method extends trivially to both animation compositing and local visibility adjustment in depth-peeled 3d scenes; the latter of which allows for the creation of impossible figures which can be viewed and manipulated in real-time.

A Layered Fabric 3D Printer for Soft Interactive Objects

We present a new type of 3D printer that can form precise, but soft and deformable 3D objects from layers of off-the-shelf fabric. Our printer employs an approach where a sheet of fabric forms each layer of a 3D object. The printer cuts this sheet along the 2D contour of the layer using a laser cutter and then bonds it to previously printed layers using a heat sensitive adhesive. Surrounding fabric in each layer is temporarily retained to provide a removable support structure for layers printed above it. This process is repeated to build up a 3D object layer by layer. Our printer is capable of automatically feeding two separate fabric types into a single print. This allows specially cut layers of conductive fabric to be embedded in our soft prints. Using this capability we demonstrate 3D models with touch sensing capability built into a soft print in one complete printing process, and a simple LED display making use of a conductive fabric coil for wireless power reception.

Physics-based motion retiming

By changing only the playback timing of a motion sequence, an animator can achieve a variety of effects that alter our perception of an event. In some scenarios, it may be important to consider physical properties of the motion when retiming (e.g., to preserve physical plausibility). However, existing retiming solutions can be quite time consuming when physical parameters are considered. This paper presents an interactive method for creating optimal motion retimings that takes into account physically based constraints and objective functions. We achieve fast performance through a precomputation phase where constraints are projected into the two-dimensional space of velocities and accelerations along the input motion path. Unlike previous approaches, our precomputation technique allows for rapid computation of plausible contact forces that result from retiming, and it also accommodates changing physical parameters. We demonstrate our approach by creating physically plausible results for changes in motion duration, manipulations of the gravity vector, and modifications of character limb masses.

A compiler for 3D machine knitting

Industrial knitting machines can produce finely detailed, seamless, 3D surfaces quickly and without human intervention. However, the tools used to program them require detailed manipulation and understanding of low-level knitting operations. We present a compiler that can automatically turn assemblies of high-level shape primitives (tubes, sheets) into low-level machine instructions. These high-level shape primitives allow knit objects to be scheduled, scaled, and otherwise shaped in ways that require thousands of edits to low-level instructions. At the core of our compiler is a heuristic transfer planning algorithm for knit cycles, which we prove is both sound and complete. This algorithm enables the translation of high-level shaping and scheduling operations into needle-level operations. We show a wide range of examples produced with our compiler and demonstrate a basic visual design interface that uses our compiler as a backend.

A 3D Printer for Interactive Electromagnetic Devices

We introduce a new form of low-cost 3D printer to print interactive electromechanical objects with wound in place coils. At the heart of this printer is a mechanism for depositing wire within a five degree of freedom (5DOF) fused deposition modeling (FDM) 3D printer. Copper wire can be used with this mechanism to form coils which induce magnetic fields as a current is passed through them. Soft iron wire can additionally be used to form components with high magnetic permeability which are thus able to shape and direct these magnetic fields to where they are needed. When fabricated with structural plastic elements, this allows simple but complete custom electromagnetic devices to be 3D printed. As examples, we demonstrate the fabrication of a solenoid actuator for the arm of a Lucky Cat figurine, a 6-pole motor stepper stator, a reluctance motor rotor and a Ferrofluid display. In addition, we show how printed coils which generate small currents in response to user actions can be used as input sensors in interactive devices.

Interactive light field painting

Since the seminal SketchPad work of Sutherland [1964], direct interaction with a computer has been compelling: we can directly touch, move, and change what we see. Direct interaction is a major contribution to the success of smartphones and tablets; yet, the world is not flat. While existing technologies can display realistic multi-view stereoscopic 3D content reasonably well [Lueder 2012], interaction within the same 3D space often requires extensive additional hardware. We present a cheap and easy system that uses the same lenslet array for both multi-view autostereoscopic display and 3D light-pen position sensing.

Laziness is a Virtue: Motion Stitching Using Effort Minimization

Given two motion-capture sequences that are to be stitched together, how can we assess the goodness of the stitching? The straightforward solution, Euclidean distance, permits counter-intuitive results because it ignores the effort required to actually make the stitch. The main contribution of our work is that we propose an intuitive, first-principles approach, by computing the effort that is needed to do the transition (laziness-effort, or ’L-score’). Our conjecture is that, the smaller the effort, the more natural the transition will seem to humans. Moreover, we propose the elastic L-score which allows for elongated stitching, to make a transition as natural as possible. We present preliminary experiments on both artificial and real motions which show that our L-score approach indeed agrees with human intuition, it chooses good stitching points, and generates natural transition paths.