Using a smartphone touchscreen to control apps mirrored to a distant display is hard, since the user cannot see where she is touching while looking at the distant screen. Tactile landmarks at the back of the phone can mitigate this problem, especially in landscape mode [3]: By moving a finger across these landmarks, the user can haptically estimate the finger position in proportion to the touchscreen. Upon pinching the thumb resting above the touchscreen towards that finger at the back, the finger position is transferred to the front and registered as a touch. However, despite proprioception, this technique leads to a shift between back and front position, denoted as pinch error. We investigated this error using different target locations, device thicknesses, and tilt angles to derive target sizes that can be acquired at a 96% success rate.

Using a smartphone for touch input to control apps and games mirrored to a distant screen is difficult, as the user cannot see where she is touching while looking at the distant display. We present HaptiCase, an interaction technique that provides back-of-device tactile landmarks that the user senses with her fingers to estimate the location of her finger in relation to the touchscreen. By pinching the thumb resting above the touch- screen to a finger at the back, the finger position is transferred to the front as the thumb touches the screen. In a study, we compared touch performance of different landmark layouts with a regular landmark-free mobile device. Using a land- mark design of dots on a 3x5 grid significantly improves eyes-free tapping accuracy and allows targets to be as small as 17.5 mm---a 14% reduction in target size---to cover 99% of all touches. When users can look at the touchscreen, land- marks have no significant effect on performance. HaptiCase is low-cost, requires no electronics, and works with unmodified software.

Tangible objects on capacitive multi-touch surfaces are usually only detected while the user is touching them. When the user lets go of such a tangible, the system cannot distinguish whether the user just released the tangible, or picked it up and removed it from the surface. We introduce PERCs, persistent capacitive tangibles that "know" whether they are currently on a capacitive touch surface or not. This is achieved by adding a small field sensor to the tangible to detect the touch screen's own, weak electromagnetic touch detection probing signal. Thus, unlike previous designs, PERCs do not get filtered out over time by the adaptive signal filters of the touch screen. We provide a technical overview of the theory be- hind PERCs and our prototype construction, and we evaluate detection rates, timing performance, and positional and angular accuracy for PERCs on a variety of unmodified, commercially available multi-touch devices.Through their affordable circuitry and high accuracy, PERCs open up the potential for a variety of new applications that use tangibles on today's ubiquitous multi-touch devices.

We report on the behavior of developers working with a live coding environment, which provides information about a program's execution immediately after each change to the source code. The live coding environment we used shows information about each individual source code line, e.g., changed variable values or truth values of conditions. In comparison to developers working in a non-live environment, those working live found and fixed bugs they introduced significantly faster. Further, working live encouraged developers to switch between editing and debugging phases more frequently.

Understanding source code is crucial for successful software maintenance, and navigating the call graph is especially helpful to understand source code [12]. We compared maintenance performance across four different development environments: an IDE without any call graph exploration tool, a Call Hierarchy tool as found in Eclipse, and the tools Stacksplorer [7]and Blaze [11]. Using any of the call graph exploration tools more developers could solve certain maintenance tasks correctly. Only Stacksplorer and Blaze, however, were also able to decrease task completion times, although the Call Hierarchy offers access to a larger part of the call graph. To investigate if this result was caused by a change in navigation behavior between the tools, we used a set of predictive models to create formally comparable descriptions of programmer navigation. The results suggest that the decrease in task completion times has been caused by Stacksplorer and Blaze promoting call graph navigation more than the Call Hierarchy tool.

Direct manipulation video navigation (DMVN) systems allow to navigate inside video scenes by spatially manipulating objects in the video. Problems arise when dealing with temporal ambiguities where a time span is projected onto a single point in image space, e.g., when objects stop moving. Existing DMVN systems deal with these cases by either disabling navigation on the paused object or by allowing jumps in the timeline. Both of these workarounds are undesirable as they introduce inconsistency or provoke loss of context. We analyze current practices regarding temporal ambiguities and introduce two new methods to visualize and navigate object pauses. User tests show that the new approaches are better suited for navigation in scenes containing temporal ambiguities and are rated higher in terms of user satisfaction.

Most presentation software uses the slide deck metaphor to create visual presentation support. Recently, canvas presentation tools such as Fly or Prezi have begun to use a zoomable free-form canvas to arrange information instead. While their effect on authoring presentations has been evaluated previously, we studied how they impact the audience. In a quantitative study, we compared audience retention and macrostructure understanding of slide deck vs. canvas presentations. We found both approaches to be equally capable of communicating information to the audience. Canvas presentations, however, were rated by participants to better aid them in staying oriented during a talk. This makes canvas presentation tools a promising slideware alternative.

We present Pinstripe, a textile user interface element for eyes-free, continuous value input on smart garments that uses pinching and rolling a piece of cloth between your fingers. The input granularity can be controlled in a natural way by varying the amount of cloth pinched. Pinstripe input elements physically consist of fields of parallel conductive lines sewn onto the fabric. This way, they can be invisible, and can be included across large areas of a garment. Pinstripe also addresses several problems previously identified in the placement and operation of textile UI elements on smart clothing. Two user studies evaluate ideal placement and orientation of Pinstripe elements on the users' garments as well as acceptance and perceived ease of use of this novel textile input technique.

We present Stacksplorer, a new tool to support source code navigation and comprehension. Stacksplorer computes the call graph of a given piece of code, visualizes relevant parts of it, and allows developers to interactively traverse it. This augments the traditional code editor by offering an additional layer of navigation. Stacksplorer is particularly useful to understand and edit unknown source code because branches of the call graph can be explored and backtracked easily. Visualizing the callers of a method reduces the risk of introducing unintended side effects. In a quantitative study, programmers using Stacksplorer performed three of four software maintenance tasks significantly faster and with higher success rates, and Stacksplorer received a System Usability Scale rating of 85.4 from participants.

Modern presentation software is still built around interaction metaphors adapted from traditional slide projectors. We provide an analysis of the problems in this application genre that presentation authors face and present Fly, a presentation tool that is based on the idea of planar information structures. Inspired by the natural human thought processes of data chunking, association, and spatial memory, Fly explores authoring of presentation documents.

We present PocketDRAGON, a demonstrator prototype that allows direct manipulation video navigation on mobile touchscreen devices. In contrast to traditional video navigation techniques, PocketDRAGON does not require any overlay UI elements that occupy valuable screen real estate and obstruct the users' view on the video. Also, direct manipulation video navigation techniques have been shown to compare favorably to the established timeline slider interfaces in terms of performance times, intuitiveness, precision, and perceived ease of use. Our demonstrator system still uses a backend server for the computationally expensive parts of the algorithms but delivers the full-fledged user experience on the mobile device.

We present DRAGON, a direct manipulation interaction technique for frame-accurate navigation in video scenes. This technique benefits tasks such as professional and amateur video editing, review of sports footage, and forensic analysis of video scenes. By directly dragging objects in the scene along their movement trajectory, DRAGON enables users to quickly and precisely navigate to a specific point in the video timeline where an object of interest is in a desired location. Examples include the specific frame where a sprinter crosses the finish line, or where a car passes a traffic light. Through a user study, we show that DRAGON significantly reduces task completion time for in-scene navigation tasks by an average of 19-42% compared to a standard timeline slider. Qualitative feedback from users is also positive, with multiple users indicating that the DRAGON interaction felt more natural than the traditional timeline slider for in-scene navigation.