Conferencias y publicaciones

Conferencias, charlas y ponencias

Why Iterators Got It All Wrong — and what we should use instead
Arno Schödl

You understand iterators, right? How would you describe them? "Iterators are used to point into sequences of elements." Sounds good? More recently, the concept of ranges has been introduced to mean anything that exposes iterators. In particular, ranges include range adaptors for lazily transforming or filtering sequences of elements, and they, too, have iterators.
All good? Unfortunately, no. The iterator concept, which we have been using since the advent of C++, is fundamentally flawed. In particular, some iterators must behave differently depending on whether they are meant to point at an element or at a boundary between elements. So elements and boundaries are really two distinct concepts. In this talk, I will convince you that the problem is real and has practical implications, make a proposal on how to fix it and show how the solution not only fixes the problem but makes for clearer code and prevents mistakes.

From Iterators To Ranges — The Upcoming Evolution Of the Standard Library
Arno Schödl

Pairs of iterators are ubiquitous throughout the C++ library. It is generally accepted that combining such a pair into a single entity usually termed Range delivers more concise and readable code. Defining the precise semantics of such Range concept proves surprisingly tricky, however. Theoretical considerations conflict with practical ones. Some design goals are mutually incompatible altogether.

A Practical Approach to Error Handling
Arno Schödl

Every program may encounter errors, some originating from internal bugs in the program, others coming from the environment the program is operating in. Ignoring all errors will make the program utterly unreliable, while treating every conceivable one introduces lots of extra complexity with little benefit. At think-cell, we have been using and refining our own principled approach to error handling, which we have not seen elsewhere. This lecture teaches our method, so that you in your next project, too, can write more reliable software with less effort.

Industrial Strength Software Hacking
Simon McPartlin

Software patching is a powerful but potentially risky method for fixing bugs, adding functionality, and improving the usability or performance of software. This lecture looks at patching software where the source code is unavailable, an activity commonly referred to as hacking. We discuss why and when such activity may be necessary before looking in detail at the design and implementation of robust patches. We finish off by describing various tools and techniques that can be used to find suitable patching locations.

std::cout is out — Why iostreams must go
Sebastian Theophil

We have recently begun to port our software to other platforms. In this process, we discovered the world of pain that are iostreams and C-style I/O. In this talk we give a short overview over why we have banished iostreams from our code base and what we have replaced them with.

C++ Memory Model
Valentin Ziegler and Fabio Fracassi

The C++ memory model defines how multiple threads interact with memory and shared data, enabling developers to reason about concurrent code in a platform independent way. The talk explains multi-threaded executions and data races in C++, how concurrent code is affected by compiler and hardware optimizations, and how to avoid undefined behavior by using locks and atomic operations. Then it focuses on different memory orders for atomic operations, their guarantees and performance implications.

C++ vs. Java
Valentin Ziegler and Fabio Fracassi

We love C++ and use it daily. In this talk we explain why – despite its reputation for complexity – C++ is conceptually a much better language than Java. Why? Because C++ knows value semantics. Because C++ has undefined behaviour. Because C++ does not enforce garbage collection. Because with C++ we can write code that is both abstract and efficient.

Publicaciones científicas

An Efficient Algorithm for Scatter Chart Labeling
Sebastian Theophil and Arno Schödl
Proceedings of AAAI 2006

This paper presents an efficient algorithm for a new variation of the point feature labeling problem. The goal is to position the largest number of point labels such that they do not intersect each other or their points. First we present an algorithm using a greedy algorithm with limited lookahead. We then present an algorithm that iteratively regroups labels, calling the first algorithm on each group, thereby identifying a close to optimal labeling order. The presented algorithm is being used in a commercial product to label charts, and our evaluation shows that it produces results far superior to those of other labeling algorithms.

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A Smart Algorithm for Column Chart Labeling
Sebastian Müller and Arno Schödl
Proceedings of SMART GRAPHICS 2005

This paper presents a smart algorithm for labeling column charts and their derivatives. To efficiently solve the problem, we separate it into two sub-problems. We first present a geometric algorithm to solve the problem of finding a good labeling for the labels of a single column, given that some other columns have already been labeled. We then present a strategy for finding a good order in which columns should be labeled, which repeatedly uses the first algorithm for some limited lookahead. The presented algorithm is being used in a commercial product to label charts, and has shown in practice to produce satisfactory results.

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Graphcut Textures: Image and Video Synthesis Using Graph Cuts
Vivek Kwatra, Arno Schödl, Irfan Essa, Greg Turk and Aaron Bobick
Proceedings of SIGGRAPH 2003

In this paper we introduce a new algorithm for image and video texture synthesis. In our approach, patch regions from a sample image or video are transformed and copied to the output and then stitched together along optimal seams to generate a new (and typically larger) output. In contrast to other techniques, the size of the patch is not chosen a-priori, but instead a graph cut technique is used to determine the optimal patch region for any given offset between the input and output texture. Unlike dynamic programming, our graph cut technique for seam optimization is applicable in any dimension. We specifically explore it in 2D and 3D to perform video texture synthesis in addition to regular image synthesis.

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Controlled Animation of Video Sprites
Arno Schödl and Irfan Essa
Proceedings of SCA 2002

In this paper we present a new approach for generating controlled animations of video sprites. Video sprites are animations created by rearranging recorded video frames of a moving object. With our technique, the user can specify animations using a flexible cost function, which is automatically optimized by repeated replacement of video sprite subsequences.

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Video Textures
Arno Schödl, Richard Szeliski, David H. Salesin and Irfan Essa
Proceedings of SIGGRAPH 2000

This paper introduces a new type of medium, called a video texture, which has qualities somewhere between those of a photograph and a video. A video texture provides a continuous infinitely varying stream of images. While the individual frames of a video texture may be repeated from time to time, the video sequence as a whole is never repeated exactly. Video textures can be used in place of digital photos to infuse a static image with dynamic qualities and explicit action.

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