In conventional 2D drawing systems, a drawing usually consists of multiple layers and is composited by rendering layers from back to front. A shape in a higher layer occludes contents in lower layers. However, shapes must have boundaries that form closed regions for occlusion. This limitation causes problems in occlusion resolution. We therefore propose a method to allow users to specify and resolve occlusion in stroke‐based drawing with boundary strokes. Rather than defining shapes, we introduce boundary strokes, which are strokes with occluding sides that work as occluding surfaces. We further introduce a series of user interactions, such as grouping, linking and inverting, on the boundary strokes to realize different occlusion effects. Geometry is then used to find the regions of occluding surfaces to resolve occlusion. The drawings are ready to be coloured, if needed. We extend our method to resolve occlusion in 2D stroke‐based inbetweening. We demonstrate the effectiveness of our method by applying it to resolve occlusion in single drawings and 2D stroke‐based inbetweening.

In computer-assisted 2D vector drawing systems, due to the precision of stroke representation, a stroke endpoint may not precisely connect to another stroke or endpoint during drawing so that the stroke endpoints become dangling. We call such dangling endpoints, gap points. With the presence of gaps on the region boundaries, regions formed by strokes frequently cannot be correctly colored using the standard 'flood fill' algorithm. In this paper, we propose a stroke-based technique to handle gaps in a vector drawing. The main contribution of our work is automatic computation of gap sizes of gap points without a predefined gap size and using a least energy method to handle gap points by estimating their relationship with surrounding strokes. Our approach consists of two major steps. Firstly, we cluster gap points in a drawing using Minimum Spanning Tree. Secondly, for each endpoint cluster, we use a least energy method together with predefined gap handling priority to estimate the connection of gap points. We demonstrate the effectiveness of our approach by applying it to line drawings with unresolved gap points.

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There are many approaches to paint line drawings. However, they are limited in dynamic color update while drawing editing. This curtails the editability of drawings and also hampers the auto-painting of animated drawings. We propose a stroke-based painting representation that associates colors with strokes. A painted drawing is represented purely with strokes, based on which region colors are resolved. With this representation, users can freely modify painted drawings with colors being updated automatically. Color stroke is further extended to auto-paint 2D animated drawings. Experimental results demonstrate the advantages of our method in painting drawings and managing colors.