StrokeStrip: Joint Parameterization and Fitting of Stroke Clusters

Dave Pagurek van Mossel¹, Chenxi Liu¹, Nicholas Vining^1,2, Mikhail Bessmeltsev³, Alla Sheffer¹

¹University of British Columbia, ²NVIDIA, ³Université de Montréal

@article{strokestrip,
	title = {StrokeStrip: Joint Parameterization and Fitting of Stroke Clusters},
	author = {Pagurek van Mossel, Dave and Liu, Chenxi and Vining, Nicholas and Bessmeltsev, Mikhail and Sheffer, Alla},
	year = 2021,
	journal = {ACM Transactions on Graphics},
	publisher = {ACM},
	address = {New York, NY, USA},
	volume = 40,
	number = 4,
	doi = {10.1145/3450626.3459777}
}

StrokeStrip jointly parameterizes clusters of strokes (a) that, together, represent strips following a single intended curve (b). We compute the parameterization of this strip (c) restricted to the domain of the input strokes (d), which we then use to produce the parameterized intended curve (d).

Usage

./strokestrip input.scap [...args]

Additional optional arguments:

• --cut: If your input strokes include sharp back-and-forth turns, this flag will use the Cornucopia library to detect and cut such strokes.
• --debug: Generate extra SVG outputs to introspect the algorithm
• --rainbow: Generate an SVG showing parameterized strokes coloured with a rainbow gradient (default is red-to-blue)
• --widths: Generate fitted widths along with centerlines
• --taper: Force fitted widths to taper to 0 at endpoints

Input format

Drawings are inputted as .scap files, which encode strokes as polylines. Strokes are contained in pairs of braces { ... }. Each stroke has a unique stroke id and a cluster id shared by all strokes that colleectively make up one intended curve. Polyline samples can omit pressure by setting it to a default value of 0.

#[width]	[height]
@[thickness]
{
	#[stroke_id]	[cluster_id]
	[x1]	[y1]	[pressure1]
	[x2]	[y2]	[pressure2]
	[x3]	[y3]	[pressure3]
	[...etc]
}
[...etc]

Example .scap inputs are found in the examples/ directory.

Stroke clusters for new .scap files can be generated using the StrokeAggregator ground truth labeling program.

Development

Dependencies

Gurobi

This package relies on the Gurobi optimization library, which must be installed and licensed on your machine. If you are at a university, a free academic license can be obtained. This project was build with Gurobi 9.0; if you are using a newer version of Gurobi, update FindGUROBI.cmake to reference your installed version (e.g. change gurobi90 to gurobi91 for version 9.1.)

Eigen 3

Ensure that Eigen is installed and that its directory is included in $CMAKE_PREFIX_PATH.

Building

StrokeStrip is configured with Cmake:

mkdir build
cd build
cmake ..
make