DIPLOMARBEIT Pivy - Embedding a Dynamic Scripting Language into a Scene Graph Library ausgef¨uhrt am Institut f¨ur Interaktive Mediensysteme der Technischen Universit¨atWien unter Anleitung von Univ.Prof. Dipl.-Ing. Dr.techn. Dieter Schmalstieg und Mag. Dr.techn. Hannes Kaufmann als verantwortlich mitwirkendem Universit¨atsassistenten, sowie unter Mitbetreuung von Dipl.-Ing. Dr.techn. Gerhard Reitmayr, durch Tamer Fahmy Urbarialgasse 1 A-2422 Pama Matrikelnummer: 9526976 Datum Unterschrift Abstract This thesis presents the design and implementation of “Pivy”: a Python language binding for the Coin scene graph library. Pivy allows for development of Coin applications in Python, interactive modification of Coin programs from within the Python interpreter at runtime and incorporation of Scripting Nodes – capable of executing Python code and callback functions – into the scene graph. Coin is a high-level 3D graphics toolkit for developing cross-platform real-time 3D visualization and visual simulation software; Coin’s properties and features are e.g. suitable for application development in the Augmented Reality (AR) domain. We differentiate between extending and embedding the Python interpreter. To create a Python extension, a C wrapper needs to be written and built as a shared library; Python then imports and makes use of this shared library at runtime. Different Python wrapping techniques and approaches – from manual wrapping to automatic wrapper generators such as SWIG – with a special focus upon large C++ libraries/frameworks applicable for Python are compared. The opposite direction is called embedding, where already existing Coin applications or libraries (written in C++) are given direct access to the Python interpreter. Both use cases are showcased and their distinction explained through Python applications using Pivy and the special SoPyScript scene graph node which has been created to allow Python code to be embedded into a regular scene graph and executed during traversal of the same. The SoPyScript scene graph node is making use of both extending and embedding techniques; it is based upon ideas of the VRML JavaScript node and can be used from either Python or C++ applications. Furthermore, the suitability and benefits of dynamically typed “scripting” languages over statically typed “system programming” languages such as C++ for Rapid Application Devel- opment (RAD) and Rapid Application Prototyping (RAP) are analyzed and demonstrated. Keywords: 3D Graphics, Augmented Reality, Scripting Language, C++, Python, Coin, Open Inventor, Rapid Application Development, Rapid Application Prototyping I Kurzfassung Die vorliegende Arbeit stellt das Design und die Implementierung von Pivy vor, einer Python- Anbindung f¨urdie Szenengraph-Bibliothek Coin. Coin ist eine plattformunabh¨angige 3D-Graphik-Bibliothek, deren hoher Abstraktionsgrad die Entwicklung von Echtzeit-Visualisierungssoftware, z.B. im Bereich von Augmented Re- ality (AR), erleichtert. Pivy erlaubt die Entwicklung von Coin-Applikationen in Python und macht es m¨oglich, Coin-Programme aus dem Python-Interpreter zur Laufzeit interaktiv zu modifizieren sowie Skript-Knoten, die Python-Code und Callback-Funktionen ausf¨uhren k¨onnen, in den Szenengraph einzuf¨ugen. Grunds¨atzlich sind zwei verschiedene Arten der Anbindung zu unterscheiden: die Erweiterung (“extension”) des Python-Interpreters und seine direkte Einbindung (“embedding”). Eine Python-Erweiterung ben¨otigteinen C-Wrapper in Form einer gemeinsam genutzten Biblio- thek, die von Python zur Laufzeit geladen und verwendet wird. Verschiedene Techniken und Ans¨atze– von der manuellen Generierung bis zur automatischen Erstellung durch Gen- eratoren wie SWIG – werden vorgestellt und verglichen. Das Hauptaugenmerk liegt dabei auf der Erweiterung von Python durch grosse C++-Bibliotheken. Umgekehrt ist es auch m¨oglich, bestehenden Coin-Applikationen oder -Bibliotheken, die in C++ geschrieben sind, durch Einbindung des Python-Interpreters direkt Zugang zu diesem zu geben. Beide Anwendungsf¨allewerden beschrieben und die Unterschiede zwischen ihnen erl¨autert. Dies geschieht anhand von Python-Applikationen, die Pivy verwenden, sowie insbesondere am Beispiel des SoPyScript-Knoten, der es erlaubt, Python-Code in einen regul¨arenSzenengraph einzubetten und bei der Traversierung auszuf¨uhren. Der SoPyScript-Knoten verwendet beide Techniken (Erweiterung und Einbindung); er basiert auf der Idee und dem Design des VRML JavaScript-Knoten und kann wie dieser sowohl von Python- wie auch C++-Applikationen verwendet werden. Des weiteren enth¨altdie Arbeit auch eine Betrachtung der grundlegenden Einsatzm¨oglichkeit von dynamisch typisierten Skriptsprachen zur schnellen Entwicklung von Applikationen und/oder Prototypen – Rapid Application Development (RAD), Rapid Application Prototyping (RAP) – und den Vorteilen von Skriptsprachen gegenueber statisch typisierten “Systemprogram- mierungssprachen” wie C++. II Acknowledgements I am full of love, so here is whom I’d like to thank: Mervat and Mohamed, my parents, for all their support and love in all those years and without whom I could have never achieved anything. Dalia and Rascha, my two sisters, who always assisted me in difficult times and greatly enriched my life. Prof. Dieter Schmalstieg, my supervisor, for giving me the opportunity to work as an undergraduate research assistant in his group at Vienna University of Technology; there I had the unique chance to learn the fundamentals of scientific work and research in the exciting field of Augmented Reality and was allowed to work on the creation of Pivy. Gerhard Reitmayr, guru and supervisor, for his invaluable help, suggestions for improve- ments, many insightful discussions which greatly influenced the design of Pivy, memorable and very enjoyable coding sessions and in general for allowing me to watch and learn from a brilliant researcher at work. The former VRGroup at Vienna University of Technology, namely Istv´anBarakonyi, Hannes Kaufmann, Florian Ledermann, Joseph Newman, Thomas Pintaric, Thomas Psik, Daniel Wagner for making our group an interesting and enjoyable workplace. Systems in Motion for all the support over all those years, without Pivy would not have been what it is today; especially Lars J. Aas, Peder Blekken, Morten Eriksen and Marius Kintel. Michael Kalkusch, who apart from being a marvelous friend over all those years, introduced me to computer graphics, making it accessible to me through his unique skill of explaining even the most complex topic in a very simple and graspable fashion (sometimes by abusing my cigarette packet and Zippo lighter to enhance his 3D explanations. ). Karin Kosina, for being such a lovely friend during all those years, making my life interesting and exciting again and who showed me that there seems to be vivid life and still sunlight on this planet outside the sphere of computer screens by opening the jalousie of my window (and forcing me to look out of my then monitor-lit room. ). Omar Medani, for dragging me with him through our study, making it so much more enjoyable and for sharing some of the most memorable and unforgettable moments in my life (from killing ourselves side by side in hopeless and lost soccer matches to taking part in mission impossible exams ;)) and being the splendid friend he was and is for so many years. III Andreas Pongratz, who helped me through troubled times in life, making math accessible to me (and showing me that there is a whole universe full of “exact definition” pitfalls hiding behind unsuspiciously simple equations such as a + b = c, ∀a, b, c ∈ C) and for being such a wonderful, reliable, altruistic friend always willing to help (and never minding to plainly name things the way they are). Very special thanks to Oyvind Rideng for his enduring patience, providing me with all the time and support I needed to finish this thesis and pushing me into the right direction when my motivation was wearing off. I’d like to thank P˚al-Robert Engnæs, who read my thesis while it was in progress and provided me with printouts containing valuable comments, feedback, suggestions for improve- ments and most importantly very constructive criticism. Of course, I cannot leave this section without at least mentioning Herbert and Gerhard Aguinaga, Maresa Dormann, Robert Fuchs, Elham Hedayati Rad, Karyn Laudisi, Barbara Langm¨uller, Herbert Schneeweiß, Terje Wiesener and all of my other friends and supporters (who got not mentioned here, because of my supervisors impatiently waiting for me to finish this thesis. *shrug*). Anyways, you know who you are! Thanks so much to all of you! IV Pivy - Embedding a Dynamic Scripting Language into a Scene Graph Library Contents 1 Introduction 1 1.1 System programming and dynamic scripting languages ............. 1 1.1.1 Contribution ................................ 4 1.2 Deficiencies of system programming languages .................. 5 1.2.1 RAP/RAD and interpreted environments for interactive 3D applications 6 1.2.2 The benefits of a Python binding ..................... 6 1.3 Development history ................................ 8 2 Related work 9 2.1 Existing 3D graphics APIs ............................. 9 2.1.1 Immediate vs. retained mode APIs .................... 9 2.2 Open Inventor/Coin - a high-level 3D graphics toolkit ............. 12 2.2.1 Overview of the Open Inventor/Coin API ................ 12 2.2.2 Scripting in Open Inventor/Coin ..................... 17 2.3 Python - a dynamic general purpose programming language .......... 20 2.3.1 Overview