Structuring and layering contour drawings of organic shapes

Abstract

Complex vector drawings serve as convenient and expressive visual representations, but they remain difficult to edit or manipulate. For clean-line vector drawings of smooth organic shapes, we describe a method to automatically extract a layered structure for the drawn object from the current or nearby viewpoints. The layers correspond to salient regions of the drawing, which are often naturally associated to 'parts' of the underlying shape. We present a method that automatically extracts salient structure, organized as parts with relative depth orderings, from clean-line vector drawings of smooth organic shapes. Our method handles drawings that contain complex internal contours with T-junctions indicative of occlusions, as well as internal curves that may either be expressive strokes or substructures. To extract the structure, we introduce a new partaware metric for complex 2D drawings, the radial variation metric, which is used to identify salient sub-parts. These sub-parts are then considered in a priority-ordered fashion, which enables us to identify and recursively process new shape parts while keeping track of Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than the author(s) must be honored. Abstracting with credit is permitted. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from permissions@acm.org. Expressive '18, August 17-19, 2018, Victoria, BC, Canada © 2018 Copyright held by the owner/author(s). Publication rights licensed to ACM. ACM ISBN 978-1-4503-5892-7/18/08. . . $15.00 https://doi.org/10.1145/3229147.3229155 their relative depth ordering. The output is represented in terms of scalable vector graphics layers, thereby enabling meaningful editing and manipulation. We evaluate the method on multiple input drawings and show that the structure we compute is convenient for subsequent posing and animation from nearby viewpoints.

Stroke‐Based Drawing and Inbetweening with Boundary Strokes

“…Entem et al . [EPCB18] completes a boundary by minimizing the total variation of curvature. Although these approaches do close boundaries, they do not exploit occlusion information in a drawing.…”

“…[SSJ*10], sparse depth (in)equalities are used to convert a 2D drawing into 2.5D with user assignments. Relative depth is also frequently inferred from 2D geometric clues, such as junction and cusp [LMY*13, EPCB18]. These automatic layering methods may fail when there exists no geometric clue.…”

“…A complex drawing can be broken down into layers that contain closed shapes. These layers are then ordered in depth so that a layer can occlude other layers below it when rendering from back to front, such as [CMB17,BAEL19] [EPCB18] completes a boundary by minimizing the total variation of curvature. Although these approaches do close boundaries, they do not exploit occlusion information in a drawing.…”