“Implementing Non-photorealistic Rendering Enhancements with Real-Time Performance” by Holger Winnemöller in February 2002 Submitted in fulfilment of the requirements for the degree of Master of Science of Rhodes University Abstract We describe quality and performance enhancements, which work in real-time, to all well-known Non- photorealistic (NPR) rendering styles for use in an interactive context. These include Comic rendering, Sketch rendering, Hatching and Painterly rendering, but we also attempt and justify a widening of the established definition of what is considered NPR. In the individual Chapters, we identify typical stylistic elements of the different NPR styles. We list problems that need to be solved in order to implement the various renderers. Standard solutions available in the literature are introduced and in all cases extended and optimised. In particular, we extend the lighting model of the comic renderer to include a specular component and introduce multiple inter-related but independent geometric approximations which greatly improve rendering performance. We implement two completely different solutions to random perturbation sketching, solve temporal coherence issues for coal sketching and find an unexpected use for 3D textures to implement hatch-shading. Textured brushes of painterly rendering are extended by properties such as stroke-direction and texture, motion, paint capacity, opacity and emission, making them more flexible and versatile. Brushes are also provided with a minimal amount of intelligence, so that they can help in maximising screen coverage of brushes. We furthermore devise a completely new NPR style, which we call super-realistic and show how sample images can be tweened in real-time to produce an image-based six degree-of-freedom renderer performing at roughly 450 frames per second. Performance values for our other renderers all lie between 10 and over 400 frames per second on home- PC hardware, justifying our real-time claim. A large number of sample screen-shots, illustrations and animations demonstrate the visual fidelity of our rendered images. In essence, we successfully achieve our attempted goals of increasing the creative, expressive and communicative potential of individual NPR styles, increasing performance of most of them, adding original and interesting visual qualities, and exploring new techniques or existing ones in novel ways. CR Categories I.3.3 [Computer Graphics] Picture/Image Generation - Bitmap and framebuffer operations I.3.3 [Computer Graphics] Picture/Image Generation - Display algorithms I.3.4 [Computer Graphics] Graphics Utilities - Paint systems I.3.5 [Computer Graphics] Computational Geometry and Object Modeling - Boundary representations I.3.5 [Computer Graphics] Computational Geometry and Object Modeling - Curve, surface, solid, and object representations I.3.7 [Computer Graphics] Three-Dimensional Graphics and Realism - Animation I.3.7 [Computer Graphics] Three-Dimensional Graphics and Realism – Color, shading, shadowing, and texture I.3.7 [Computer Graphics] Three-Dimensional Graphics and Realism – Hidden line/surface removal I.3.7 [Computer Graphics] Three-Dimensional Graphics and Realism – Virtual Reality I.4.3 [Image Processing and Computer Vision] Enhancements – Geometric Correction Additional Keywords 3D Texturing; Brownian motion; Brush-stroke extensions; Comic, Cartoon, Coal, Pencil, Chalk, Hatching, Painterly rendering; Control-vertex acquisition & identification; Edge-fading; Importance- functions; Level-of-detail measure; Linear, bi-linear, tri-linear interpolation; Morphing; Natural media simulation; Non-photorealistic rendering; Perspective-correction; Phong lighting; Projective texturing; Realistic rendering; Real-time; Reference-image acquisition; Super-realistic rendering; Temporal coherence; Textured brushes; Tweening; Uncertainty-functions. Acknowledgements and Legalities I would like to sincerely thank my supervisor Shaun Bangay for his loyal support, his cool vote of confidence and thought-provoking discussions; my girl-friend Danielle for her unconditional love and support; my parents for furnishing me with great values and always believing in me; Colin Dembovsky for years of excellent friendship; the Computer Science Department at Rhodes University for their friendliness and openness to new and exciting ideas; and Rhodes University for its vision, support, attitude and morale. The copyright for this entire document and all of its content lies solely with Holger Winnemöller. Duplication of the whole document or parts thereof, by electronic, mechanical or other means is granted exclusively to Rhodes University and for educational purposes only, provided that no part of it is changed or omitted. Written permission of the author is required for all other purposes or by any other parties. All models used in this project are publicly available (see Section 9.6 for source-references) in their original form and have subsequently been modified to suit our requirements. All images and figures are created and copyright by Holger Winnemöller, except where explicitly stated otherwise. i Table of Contents 1 INTRODUCTION ........................................................................................................................1 1.1 PROBLEM STATEMENT .............................................................................................................1 1.2 A HISTORY OF GRAPHICS EVOLUTION ([103]) ...........................................................................2 1.3 DEFINITIONS OF TERMS ............................................................................................................2 1.3.1 Photorealism vs. Non-photorealism .................................................................................3 1.3.2 Real-time.........................................................................................................................4 1.4 MOTIVATION FOR NON-PHOTOREALISTIC RENDERING ...............................................................5 1.4.1 Comic Style .....................................................................................................................6 1.4.2 Sketching.........................................................................................................................7 1.4.3 Painterly .........................................................................................................................9 1.5 DOCUMENT STRUCTURE ..........................................................................................................9 1.6 SUMMARY............................................................................................................................. 10 2 RELATED WORK..................................................................................................................... 11 2.1 NON-PHOTOREALISTIC TECHNIQUES....................................................................................... 11 2.1.1 General......................................................................................................................... 11 2.1.2 Comic Style ................................................................................................................... 12 2.1.3 Sketching....................................................................................................................... 13 2.1.4 Painting ........................................................................................................................ 17 2.1.5 Others........................................................................................................................... 19 2.2 TECHNICAL TERMS ................................................................................................................ 20 2.2.1 Object Description ........................................................................................................ 20 2.2.2 Standard Vectors........................................................................................................... 21 2.2.3 Edges............................................................................................................................ 21 2.2.4 Faces, Triangles and Polygons ...................................................................................... 23 2.3 GENERAL TECHNIQUES .......................................................................................................... 24 2.3.1 Custom Clear Operation................................................................................................ 24 2.3.2 Hidden Line Removal with Background preservation ..................................................... 26 2.4 PERFORMANCE TESTING ........................................................................................................ 27 2.4.1 Set-up............................................................................................................................ 28 2.4.2 Objects.......................................................................................................................... 29 2.4.3 Default Renderer........................................................................................................... 31 2.5 SUMMARY............................................................................................................................. 33 3 COMIC STYLE.......................................................................................................................... 35 3.1 INTRODUCTION.....................................................................................................................