Publications

Crafting satisfying narratives while preserving player freedom of action is a longstanding challenge for computer games. Many games use a quest structure, allowing players to experience content nonlinearly. However, this risks creating disjointed stories when side quests only minimally integrate with the main story. We propose a flexible, scene-based story system that reacts dynamically to the player's actions. In the proposed system, stories are defined within a graph where nodes represent scenes and edges represent causality. Nodes are tagged with information including possible locations for the scene, the plans or goals connected to the scene, and the agents and objects involved in the scene. At any time, the distance from the player's current game state to nodes in the story graph is measured according to five dimensions of nonlinearity: time, space, causality, agents involved, and the player's goal. The system will use the distance to determine what nodes should be available at any given time. Scenes will be modified dynamically according to when and where they ultimately take place, ensuring that each node has a narrative connection to its predecessors. This system allows for potentially connected stories driven by player action, leading to a more cohesive emergent story.

@poster{Carmichael:13:CES,
    author = {Carmichael, Gail and Mould, David},
    title = {Coherent Emergent Stories},
    booktitle = {GRAND},
    year = 2013,
}
                    

Study of images, in contexts as widespread as medicine, geography, and art history, demands attention to detail and exercise of memory. Presented with traditional textbooks, students have difficulty concentrating for the long periods of time needed to absorb the information. This paper presents a sketch-based game for learning images. We tested the game in the domain of art history, and in a controlled user study, we found that it dramatically increased the time that participants chose to spend learning about historical paintings. The increase in study time was accompanied by a proportionate increase in information retention and familiarity with the images.

@inproceedings{Wasson:2013:SGA:2487381.2487384,
    author = {Wasson, Rajinder and Mould, David and Biddle, Robert and Martinez, Cristina S.},
    title = {A Sketching Game for Art History Instruction},
    booktitle = {Proceedings of the International Symposium on Sketch-Based Interfaces and Modeling},
    pages = {23--31},
    year = 2013,
}
                    

Image abstraction traditionally eliminates texture, flattening gradients and removing small-scale details. However, abstracting while preserving irregular silhouettes and medium-scale details can produce a richer abstracted image. We propose a variant of geodesic image filtering which preserves the locally strongest edges, leading to preservation of both strong edges and weak edges depending on the surrounding context.

@article{Mould:2013:SSE:2493621.2493778,
    author = {Mould, David},
    title = {Image and Video Abstraction using Cumulative Range Geodesic Filtering},
    journal = {Computers and Graphics},
    volume = {37},
    number = {5},
    pages = {413--430},
    year = 2013,
}
                    

User control over fluid simulations is a long-standing research problem in computer graphics. Applications in games and films often require recognizable creatures or objects formed from smoke, water, or flame. This paper describes a two-layer approach to the problem, in which a bulk velocity drives a particle system towards a target distribution, while simultaneously a vortex particle simulation adds recognizable fluid motion.

@inproceedings{Madill:2013:TPC:2532129.2532151,
    author = {Madill, Jamie and Mould, David},
    title = {Target Particle Control of Smoke Simulation},
    booktitle = {Proceedings of the 2013 Graphics Interface Conference},
    pages = {125--132},
    year = 2013,
}
                    

Non-photorealistic rendering (NPR) has been used to produce stylized images, e.g., in a stippled or painted style. To evaluate NPR algorithms, similarity measurements used in image processing have been employed to assess the quality of rendered images. However, there is no standard objective measurement of stylization quality. In many cases, raw side-by-side comparisons are used to demonstrate improvements in aesthetic quality. This means of comparison often fails to be persuasive due to the small size of demonstrations and the subjective choice of images. We conducted a user study and examined responses of 30 subjects in order to determine two things: whether there exists a relationship between the structural quality and aesthetic quality of non-colored non-photorealistic images; and whether the choice of images matters for side-by-side comparisons.

@inproceedings{Li:2013:SAN:2532129.2532160,
    author = {Li, Hua and Mould, David and Davies, Jim},
    title = {Structure and Aesthetics in Non-photorealistic Images},
    booktitle = {Proceedings of the 2013 Graphics Interface Conference},
    pages = {181--188},
    year = 2013,
}
                    

Partition of unity parametrics (PUPs) are a recent framework designed for geometric modeling. We propose employing PUPs for procedural texture synthesis, taking advantage of the framework's guarantees of high continuity and local support. Using PUPs to interpolate among data values distributed through the plane, the problem of texture synthesis can be approached from the perspective of point placement and attribute assignment. We present several alternative mechanisms for point distribution and demonstrate how the system is able to produce a variety of distinct classes of texture, including analogs to cellular texture, Perlin noise, and progressively-variant textures.

@inproceedings{Caron:2013:PUP:2532129.2532159,
    author = {Caron, Jacquelin and Mould, David},
    title = {Partition of Unity Parametrics for Texture Synthesis},
    booktitle = {Proceedings of the 2013 Graphics Interface Conference},
    pages = {173--179},
    year = 2013,
}
                    

Computer science still faces a significant gender imbalance with women earning less than 20% of degrees. To address this issue, we designed an educational computer game, Gram's House, which aims to teach CS concepts and demonstrate how CS can be used for social good. We will introduce the game concept, demonstrate two early prototypes, report results of a pilot study, and share our future plans, including procedural content generation.

@inproceedings{Carmichael:2013:GHEG,
    author = {Carmichael, Gail and Gardiner, Carolee S.},
    title = {Gram's House: Encouraging Girls to Consider Computer Science Through Games},
    booktitle = {Grace Hopper Celebration of Women in Computing},
    year = 2013,
}
                    

Line-drawing usually focuses on creating back-and-white lines which are able to trace out objects by outlining features or matching tones. However, none of the algorithms proposed before can produce parallel lines that change spacings and thicknesses with neighbors automatically. We proposed a coordinated particle system which is capable of tracing out features and details with parallel lines changing directions and thicknesses automatically. To match tones and generate parallel lines, we allow new particles to be created in areas that have small spacings and let particles be terminated when collisions occur or when the desired spacings become larger. Natural yet irregular patterns are achieved by adding some randomness to particles' directions.

@report{wei13thesis,
    author = {Chujia Wei},
    title = {Coordinated Particle System},
    booktitle = {Carleton University},
    year = 2013,
}
                    

Image abstraction traditionally eliminates texture, but doing so ignores the more elegant alternative of texture indication, e.g., suggesting the presence of texture through irregular silhouettes and locally chosen details. We propose a variant of geodesic image filtering which preserves the locally strongest edges, leading to preservation of both strong edges and weak edges depending on the surrounding context.

@inproceedings{Mould:2012:TA:2330147.2330162,
    author = {Mould, David},
    title = {Texture-preserving Abstraction},
    booktitle = {Proceedings of the Symposium on Non-Photorealistic Animation and Rendering},
    pages = {75--82},
    year = 2012,
}
                    

Art history students see hundreds of different images and must memorize the details and significance of each one. Thus, learning the images takes a significant amount of time that students are often not willing to spend. However, games do a great job in motivating people to spend a lot of time performing repetitive tasks. We designed a game prototype aimed at art history students in which the users sketch on the images, encouraging them to spend more time with the images and drawing their attention to specific areas in them. The sketching task involves the user finding and tracing a glyph; the tracing requires precision, forcing the user to focus on specific parts of the image as well as attending to the image as a whole. Once the user completes the sketching of the glyph successfully, new information is unlocked and displayed. Providing information that relates to specific areas and features of an image can prevent important details from going unnoticed and helps the user with the overall understanding of the image. To test the effectiveness of our game, which was developed with images and content provided by an art history professor, we performed a user study with 25 university students. The user study showed some images through the sketching game mechanics and others in a static textbook style. We found that participants spent more time and remembered more details on the sketch-based images compared to the textbook-style images.

@poster{wasson12,
    author = {Raj Wasson and David Mould},
    title = {Sketch and Learn Poster},
    booktitle = {GRAND Conference},
    year = 2012,
}
                    

We propose a system for arranging images from a database into a collage that resembles some target image. These collages exploit large scale visual correspondences between the target image and the images in the database. We ensure that images of multiple sizes are used and are combined so that boundaries between images are not immediately apparently; as a result, the final collage consists of irregularly shaped image sections. The final collages contain a dynamic mixture of textures, images, and shapes that is in contrast to the geometric and regular character of many photomosaic techniques. In service of these tasks, we propose a fast scale-based method for querying an image library, a novel method for composing multiple images using geodesic distance Voronoi tesselations, and a novel base/detail method for shifting the colors of the final collage so that the target image is more accurately represented.

@inproceedings{Miller:2012:ADP:2328888.2328908,
    author = {Miller, Jordan and Mould, David},
    title = {Accurate and Discernible Photocollages},
    booktitle = {Proceedings of the Eighth Annual Symposium on Computational Aesthetics in Graphics, Visualization, and Imaging},
    pages = {115--124},
    year = 2012,
}
                    

Augmented reality has recently become a popular interface for various learning applications, but it is not always clear that AR is the right choice. We provide a theoretical grounding that explains the underlying value of AR for learning and identify when it is a suitable interface. Our list of operational design advantages includes AR's use of reality, virtual flexibility, invisible interface, and spatial awareness. This list is backed by four underlying cognitive theories: mental models and distributed, situated, and embodied cognition. We argue that the more design advantages a learning system incorporates, the better AR works as an interface. We also identify a set of questions to be used in the design and evaluation of AR projects. With this, we can begin to design AR for learning more purposefully.

@inproceedings{CarmBiddMoul2012aw,
    author = {Carmichael, Gail and Biddle, Robert and Mould, David},
    title = {Understanding the Power of Augmented Reality for Learning},
    booktitle = {Proceedings of World Conference on E-Learning in Corporate, Government, Healthcare, and Higher Education 2012},
    pages = {1761--1771},
    year = 2012,
}
                    

In this work we propose both implicit and parametric curves to represent aesthetic curves inscribed by Voronoi cells in R-2. A user survey was conducted to determine, which class of curves are generally accepted as the more aesthetic. We present the curves, the survey results, and the implications for future work on simulating sponge like volumes

@inproceedings{Wyvill:2012:DAI,
    author = {Brian Wyvill and Paul Kry and Raimund Seidel and David Mould},
    title = {Determining an aesthetic inscribed curve},
    booktitle = {Proceedings of the Eighth Annual Symposium on Computational Aesthetics in Graphics, Visualization, and Imaging},
    pages = {63--70},
    year = 2012,
}
                    

Non-photorealistic rendering (NPR) algorithms are used to produce stylized images, and have generally been evaluated on the aesthetic qualities of the resulting images. NPR-produced images have been used for aesthetic and practical reasons in media intended to produce an emotional reaction in a consumer (e.g., computer games, films, advertisements, and websites); however, it is not understood how non-photorealistic rendering affects the emotion portrayed in an image. We conducted a study of subjective emotional response and visual attention to five common NPR approaches, two blurring techniques, and the original image with 42 participants, and found that the NPR algorithms dampened participants' emotional responses in terms of arousal (activation) and valence (pleasure). Gaze data revealed that NPR rendering of images might reduce emotional response to an image by producing confusion, creating distracting visual artifacts, causing the loss of meaningful semantic information, or causing users to lose interest in the resulting image.

@article{Mould:2012:SSC:2350361.2350451,
    author = {Mould, David and Mandryk, Regan L. and Li, Hua},
    title = {Emotional Response and Visual Attention to Non-photorealistic Images},
    journal = {Computers and Graphics},
    volume = {36},
    number = {6},
    pages = {658--672},
    year = 2012,
}
                    

Partition of unity parametrics (PUPs) are a recent framework designed for geometric modeling. We propose employing PUPs for procedural texture synthesis. Using PUPs to interpolate among data values distributed through the plane, the problem of texture synthesis can be approached from the perspective of point placement and attribute assignment.

@poster{caron12PUP,
    author = {Jacquelin Caron and David Mould},
    title = {Partition of Unity Parametrics for Texture Synthesis Poster},
    booktitle = {GRAND},
    year = 2012,
}
                    

We present a method to generate models for trees in which we first create a weighted graph, organized based on the Yao graph, then place endpoints and root point and plan least-cost paths from endpoints to the root point. The collection of resulting paths forms a branching structure. We create a hierarchical tree structure by placing subgraphs around each endpoint and beginning again through some number of iterations. Powerful control over the global shape of the resulting tree is exerted by the shape of the initial graph, composed of simple geometric primitives arranged in part manually and in part procedurally. Users can create desired variations by adjusting the initial graph shape; more subtle variations can be accomplished by modifying parameters of the graph and subgraph creation processes and by changing the endpoint distribution mechanisms. The method is capable of matching a desired target structure with a little manual effort, and can easily generate a large group of slightly different models under the same parameter settings. Environmental effects can also be incorporated into the models by automatic parameter adjustment. The final trees are both intricate and convincingly realistic in appearance.

@article{Xu:2012:GIP:2405851.2406083,
    author = {Xu, Ling and Mould, David},
    title = {A Procedural Method for Irregular Tree Models},
    journal = {Computers and Graphics},
    volume = {36},
    number = {8},
    pages = {1036--1047},
    year = 2012,
}
                    

Art history students see hundreds of different images and must memorize the significant details of each one. Their learning potential would be increased by combining the pleasures and addictive properties of a video game with a mechanism to interact with the images while learning the details. This thesis describes the design and implementation of an educational framework, called Sketch and Learn, that applies effective game mechanics to motivate the player to spend more time viewing images and remember the accompanying details. We had 25 students participate in a game using Sketch and Learn images and textbook-style images. Our results showed that participants spent three times more time on Sketch and Learn images and remembered 60% more of their details. The Sketch and Learn framework has great potential as a learning tool to help students of any culture or language develop skills and knowledge in any subject matter that involves images.

@thesis{wasson12thesis,
    author = {Raj Wasson},
    title = {Sketch and Learn: a sketch based game framework for studying images},
    booktitle = {Carleton University},
    year = 2012,
}