EG 2024 - Short Papers
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Item 3D Reconstruction from Sketch with Hidden Lines by Two-Branch Diffusion Model(The Eurographics Association, 2024) Fukushima, Yuta; Qi, Anran; Shen, I-Chao; Gryaditskaya, Yulia; Igarashi, Takeo; Hu, Ruizhen; Charalambous, PanayiotisWe present a method for sketch-based modelling of 3D man-made shapes that exploits not only the commonly considered visible surface lines but also the hidden lines typical for technical drawings. Hidden lines are used by artists and designers to communicate holistic shape structure. Given a single viewpoint sketch, leveraging such lines allows us to resolve the ambiguity of the shape's surfaces hidden from the observer. We assume that the separation into visible and hidden lines is given, and focus solely on how to leverage this information. Our strategy is to mingle two distinct diffusion networks: one generates denoized occupancy grid estimates from a visible line image, whilst the other generates occupancy grid estimates based on contextualized hidden lines unveiling the occluded shape structure. We iteratively merge noisy estimates from both models in a reverse diffusion process. Importantly, we demonstrate the importance of what we call a contextualized hidden lines image over just a hidden lines image. Our contextualized hidden lines image contains hidden lines and silhouette lines. Such contextualization allows us to achieve superior performance to a range of alternative configurations and reconstruct hidden holes and hidden surfaces.Item Accurate Boundary Condition for Moving Least Squares Material Point Method using Augmented Grid Points(The Eurographics Association, 2024) Toyota, Riku; Umetani, Nobuyuki; Hu, Ruizhen; Charalambous, PanayiotisThis paper introduces an accurate boundary-handling method for the moving least squares (MLS) material point method (MPM), which is a popular scheme for robustly simulating deformable objects and fluids using a hybrid of particle and grid representations coupled via MLS interpolation. Despite its versatility with different materials, traditional MPM suffers from undesirable artifacts around wall boundaries, for example, particles pass through the walls and accumulate. To address these issues, we present a technique inspired by a line handler for MLS-based image manipulation. Specifically, we augment the grid by adding points along the wall boundary to numerically compute the integration of the MLS weight. These additional points act as background grid points, improving the accuracy of the MLS interpolation around the boundary, albeit with a marginal increase in computational cost. In particular, our technique makes the velocity perpendicular to the wall nearly zero, preventing particles from passing through the wall. We compare the boundary behavior of 2D simulation against that of naïve approach.Item DeepIron: Predicting Unwarped Garment Texture from a Single Image(The Eurographics Association, 2024) Kwon, Hyun-Song; Lee, Sung-Hee; Hu, Ruizhen; Charalambous, PanayiotisRealistic reconstruction of 3D clothing from an image has wide applications, such as avatar creation and virtual try-on. This paper presents a novel framework that reconstructs the texture map for 3D garments from a single garment image with pose. Since 3D garments are effectively modeled by stitching 2D garment sewing patterns, our specific goal is to generate a texture image for the sewing patterns. A key component of our framework, the Texture Unwarper, infers the original texture image from the input garment image, which exhibits warping and occlusion of the garment due to the user's body shape and pose. This is effectively achieved by translating between the input and output images by mapping the latent spaces of the two images. By inferring the unwarped original texture of the input garment, our method helps reconstruct 3D garment models that can show high-quality texture images realistically deformed for new poses. We validate the effectiveness of our approach through a comparison with other methods and ablation studies.Item Driller: An Intuitive Interface for Designing Tangled and Nested Shapes(The Eurographics Association, 2024) Butler, Tara; Guehl, Pascal; Parakkat, Amal Dev; Cani, Marie-Paule; Hu, Ruizhen; Charalambous, PanayiotisThe ability to represent not only isolated shapes but also shapes that interact is essential in various fields, from design to biology or anatomy. In this paper, we propose an intuitive interface to control and edit complex shape arrangements. Using a set of pre-defined shapes that may intersect, our ''Driller'' interface allows users to trigger their local deformation so that they rest on each other, become tangled, or even nest within each other. Driller provides an intuitive way to specify the relative depth of different shapes beneath user-selected points of interest by setting their local depth ordering perpendicularly to the camera's viewpoint. Deformations are then automatically generated by locally propagating these ordering constraints. In addition to being part of the final arrangement, some of the shapes can be used as deformers, which can be later deleted to help sculpt the target shapes. We implemented this solution within a sketch-based modeling system designed for novice users.Item Efficient and Accurate Multi-Instance Point Cloud Registration with Iterative Main Cluster Detection(The Eurographics Association, 2024) Yu, Zhiyuan; Zheng, Qin; Zhu, Chenyang; Xu, Kai; Hu, Ruizhen; Charalambous, PanayiotisMulti-instance point cloud registration is the problem of recovering the poses of all instances of a model point cloud in a scene point cloud. A traditional solution first extracts correspondences and then clusters the correspondences into different instances. We propose an efficient and robust method which clusters the correspondences in an iterative manner. In each iteration, our method first computes the spatial compatibility matrix between the correspondences, and detects its main cluster. The main cluster indicates a potential occurrence of an instance, and we estimate the pose of this instance with the correspondences in the main cluster. Afterwards, the correspondences are removed to further register new instances in the following iterations. With this simplistic design, our method can adaptively determine the number of instances, achieving significant improvements on both efficiency and accuracy.Item Emotional Responses to Exclusionary Behaviors in Intelligent Embodied Augmented Reality Agents(The Eurographics Association, 2024) Apostolou, Kalliopi; Milata, Vaclav; Škola, Filip; Liarokapis, Fotis; Hu, Ruizhen; Charalambous, PanayiotisThis study investigated how interactions with intelligent agents, embodied as augmented reality (AR) avatars displaying exclusionary behaviors, affect users' emotions. Six participants engaged using voice interaction in a knowledge acquisition scenario in an AR environment with two ChatGPT-driven agents. The gaze-aware avatars, simulating realistic body language, progressively demonstrated social exclusion behaviors. Although not statistically significant, our data suggest a post-interaction emotional shift, manifested by decreased positive and negative affect-aligning with previous studies on social exclusion. Qualitative feedback revealed that some users attributed the exclusionary behavior of avatars to system glitches, leading to their disengagement. Our findings highlight challenges and opportunities for embodied intelligent agents, underscoring their potential to shape user experiences within AR, and the broader extended reality (XR) landscape.Item EUROGRAPHICS 2024: Short Papers Frontmatter(Eurographics Association, 2024) Hu, Ruizhen; Charalambous, Panayiotis; Hu, Ruizhen; Charalambous, PanayiotisItem FACTS: Facial Animation Creation using the Transfer of Styles(The Eurographics Association, 2024) Saunders, Jack R.; Namboodiri, Vinay P.; Hu, Ruizhen; Charalambous, PanayiotisThe ability to accurately capture and express emotions is a critical aspect of creating believable characters in video games and other forms of entertainment. Traditionally, this animation has been achieved with artistic effort or performance capture, both requiring costs in time and labor. More recently, audio-driven models have seen success, however, these often lack expressiveness in areas not correlated to the audio signal. In this paper, we present a novel approach to facial animation by taking existing animations and allowing for the modification of style characteristics. We maintain the lip-sync of the animations with this method thanks to the use of a novel viseme-preserving loss. We perform quantitative and qualitative experiments to demonstrate the effectiveness of our work.Item Fast Dynamic Facial Wrinkles(The Eurographics Association, 2024) Weiss, Sebastian; Chandran, Prashanth; Zoss, Gaspard; Bradley, Derek; Hu, Ruizhen; Charalambous, PanayiotisWe present a new method to animate the dynamic motion of skin micro wrinkles under facial expression deformation. Since wrinkles are formed as a reservoir of skin for stretching, our model only deforms wrinkles that are perpendicular to the stress axis. Specifically, those wrinkles become wider and shallower when stretched, and deeper and narrower when compressed. In contrast to previous methods that attempted to modify the neutral wrinkle displacement map, our approach is to modify the way wrinkles are constructed in the displacement map. To this end, we build upon a previous synthetic wrinkle generator that allows us to control the width and depth of individual wrinkles when generated on a per-frame basis. Furthermore, since constructing a displacement map per frame of animation is costly, we present a fast approximation approach using pre-computed displacement maps of wrinkles binned by stretch direction, which can be blended interactively in a shader. We compare both our high quality and fast methods with previous techniques for wrinkle animation and demonstrate that our work retains more realistic details.Item A Fresnel Model for Coated Materials(The Eurographics Association, 2024) Vernooij, Hannes B.; Hu, Ruizhen; Charalambous, PanayiotisWe propose a novel analytical RGB model for rendering coated conductors, which provides improved accuracy of Fresnel reflectance in BRDFs. Our model targets real-time path tracing and approximates the Fresnel reflectance curves with noticeably more accuracy than Schlick's approximation using Lazanyi's error compensation term and the external media adjustment. We propose an analytical function with coefficients fitted to measured spectral datasets describing the complex index of refraction for conductors. We utilize second-order polynomials to fit the model, subsequently compressing the fitted coefficients to optimize memory requirements while maintaining quality. Both quantitative and visual results affirm the efficacy of our model in representing the Fresnel reflectance of the tested conductors.Item A Generative Approach to Light Placement for Street Lighting(The Eurographics Association, 2024) Evangelou, Iordanis; Vitsas, Nick; Papaioannou, Georgios; Gkaravelis, Anastasios; Hu, Ruizhen; Charalambous, PanayiotisThe design of plausible and effective street lighting configurations for arbitrary urban sites should attain predetermined illuminance levels and adhere to specific layout intentions and functional requirements. This task can be time consuming, even for automated solutions, since there exists an one-to-many mapping between illumination goals and lighting options. In this work, we propose a generative approach for this task, based on an adversarial optimisation scheme. Our proposed method effectively overcomes these task-specific limitations by providing a range of viable solutions that adhere to the input constraints and can be generated within an interactive design life cycle.Item A Highly Adaptable and Flexible Rendering Engine by Minimum API Bindings(The Eurographics Association, 2024) Kim, Taejoon; Hu, Ruizhen; Charalambous, PanayiotisThis paper presents a method for embedding a rendering engine into different development environments with minimal API bindings. The method separates the engine interfaces into two levels: System APIs and User APIs. System APIs are the lowlevel functions that enable communication between the engine and the user environment, while User APIs are the high-level functions that provide rendering and beyond rendering functionalities to the user. By minimizing the number of System APIs, the method simplifies the adaptation of the engine to various languages and platforms. Its applicability and flexibility are demonstrated by the successful embedding the engine in multiple environments, including C/C++, C#, Python, Javascript, and Matlab. It also demonstrates its versatility in diverse forms such as CLI renderers, Web GUI framework-based renderers, remote renderers, physical simulations, and more, while also enabling the easy adoption of other rendering algorithms to the engine.Item An Inverse Procedural Modeling Pipeline for Stylized Brush Stroke Rendering(The Eurographics Association, 2024) Li, Hao; Guan, Zhongyue; Wang, Zeyu; Hu, Ruizhen; Charalambous, PanayiotisStylized brush strokes are crucial for digital artists to create drawings that express a desired artistic style. To obtain the ideal brush, artists need to spend much time manually tuning parameters and creating customized brushes, which hinders the completion, redrawing, or modification of digital drawings. This paper proposes an inverse procedural modeling pipeline for predicting brush parameters and rendering stylized strokes given a single sample drawing. Our pipeline involves patch segmentation as a preprocessing step, parameter prediction based on deep learning, and brush generation using a procedural rendering engine. Our method enhances the overall experience of digital drawing recreation by empowering artists with more intuitive control and consistent brush effects.Item Modern Dance Retargeting using Ribbons as Lines of Action(The Eurographics Association, 2024) Vialle, Manon; Ronfard, Rémi; Skouras, Melina; Hu, Ruizhen; Charalambous, PanayiotisWe present a method for retargetting dancing characters represented as articulated skeletons with possibly different morphologies and topologies. Our approach relies on the use of flexible ribbons that can bend and twist as an intermediate representation, and that can be seen as animated lines of action. These ribbons allow us to abstract away the specific morphology of the bodies and to well transmit the fluidity of modern dance movement from one character to another.Item Neural Moment Transparency(The Eurographics Association, 2024) Tsopouridis, Grigoris; Vasilakis, Andreas Alexandros; Fudos, Ioannis; Hu, Ruizhen; Charalambous, PanayiotisWe have developed a machine learning approach to efficiently compute per-fragment transmittance, using transmittance composed and accumulated with moment statistics, on a fragment shader. Our approach excels in achieving superior visual accuracy for computing order-independent transparency (OIT) in scenes with high depth complexity when compared to prior art.Item Real-time Seamless Object Space Shading(The Eurographics Association, 2024) Li, Tianyu; Guo, Xiaoxin; Hu, Ruizhen; Charalambous, PanayiotisObject space shading remains a challenging problem in real-time rendering due to runtime overhead and object parameterization limitations. While the recently developed algorithm by Baker et al. [BJ22] enables high-performance real-time object space shading, it still suffers from seam artifacts. In this paper, we introduce an innovative object space shading system leveraging a virtualized per-halfedge texturing schema to obviate excessive shading and preclude texture seam artifacts. Moreover, we implement ReSTIR GI on our system (see Figure 1), removing the necessity of temporally reprojecting shading samples and improving the convergence of areas of disocclusion. Our system yields superior results in terms of both efficiency and visual fidelity.Item Skeleton-Aware Skin Weight Transfer for Helper Joint Rigs(The Eurographics Association, 2024) Cao, Ziyuan; Mukai, Tomohiko; Hu, Ruizhen; Charalambous, PanayiotisWe propose a method to transfer skin weights and helper joints from a reference model to other targets. Our approach uses two types of spatial proximity to find the correspondence between the target vertex and reference mesh regions. The proposed method first generates a guide weight map to establish a relationship between the skin vertices and skeletal joints using a standard skinning technique. The correspondence between the reference and target skins is established using vertex-to-bone projection and bone-to-skin ray-casting using the guide weights. This method enables fully automated and smooth transfer of skin weight between human-like characters bound to helper joint rigs.Item SPnet: Estimating Garment Sewing Patterns from a Single Image of a Posed User(The Eurographics Association, 2024) Lim, Seungchan; Kim, Sumin; Lee, Sung-Hee; Hu, Ruizhen; Charalambous, PanayiotisThis paper presents a novel method for reconstructing 3D garment models from a single image of a posed user. Previous studies that have primarily focused on accurately reconstructing garment geometries to match the input garment image may often result in unnatural-looking garments when deformed for new poses. To overcome this limitation, our work takes a different approach by inferring the fundamental shape of the garment through sewing patterns from a single image, rather than directly reconstructing 3D garments. Our method consists of two stages. Firstly, given a single image of a posed user, it predicts the garment image worn on a T-pose, representing the baseline form of the garment. Then, it estimates the sewing pattern parameters based on the T-pose garment image. By simulating the stitching and draping of the sewing pattern using physics simulation, we can generate 3D garments that can adaptively deform to arbitrary poses. The effectiveness of our method is validated through ablation studies on the major components and a comparison with other methods.Item StarDEM: Efficient Discrete Element Method for Star-shaped Particles(The Eurographics Association, 2024) Schreck, Camille; Lefebvre, Sylvain; Jourdan, David; Martínez, Jonàs; Hu, Ruizhen; Charalambous, PanayiotisGranular materials composed of particles with complex shapes are challenging to simulate due to the high number of collisions between the particles. In this context, star shapes are promising: they cover a wide range of geometries from convex to concave and have interesting geometric properties. We propose an efficient method to simulate a large number of identical star-shaped particles. Our method relies on an effective approximation of the contacts between particles that can handle complex shapes, including highly non-convex ones. We demonstrate our method by implementing it in a 2D simulation using the Discrete Element Method, both on the CPU and GPU.Item Utilizing Motion Matching with Deep Reinforcement Learning for Target Location Tasks(The Eurographics Association, 2024) Lee, Jeongmin; Kwon, Taesoo; Shin, Hyunju; Lee, Yoonsang; Hu, Ruizhen; Charalambous, PanayiotisWe present an approach using deep reinforcement learning (DRL) to directly generate motion matching queries for longterm tasks, particularly targeting the reaching of specific locations. By integrating motion matching and DRL, our method demonstrates the rapid learning of policies for target location tasks within minutes on a standard desktop, employing a simple reward design. Additionally, we propose a unique hit reward and obstacle curriculum scheme to enhance policy learning in environments with moving obstacles.