Create beautiful boards with Gerbolyze
Today, there is an increasingly large crowd of people who do artistic circuit board designs. People who fuse the roles of engineer and artist. Unitl today, circuit board design tools mostly ignore this use case and present a multitude of obstacles for such use. Gerbolyze finally solves this problem and presents an integrated solution for artistic PCB design that is compatible with real designer's workflows on one side and with real electronic design automation software on the other side.
This design was created from a digital artwork in a raster image file after circuit board manufacturer PCBWay offered me some free boards. The artwork was pre-processed using a raster graphics tool: It was split into layers for the different colors. Then, its color components were adjusted for brightness and contrast and finally passed through a raster-based halftone filter. The resulting file was then converted into circuit board manufacturing files using Gerbolyze.
Thirty years ago, the world of printed circuit board design was revolutionized by the introduction of computer aided design tools. These tools enabled extremely complex designs through automation features like autorouting and through automatic design rule checking to weed out human error. While the first such tools were still very limited, their capabilites quickly grew and a few years after their introduction modern electronics design without computers was already unthinkable.
Today, circuit board design programs can look back on a rich history and have accumulated a healty amount of expert knowledge in their design. Despite their difficult economic niche, even free software design tools have grown to become usable for advanced designs. However, all modern circuit board design tools are severely lacking in one area: That of artistic design. Many design assumptions are hard-wired deep into their design: Traces should be at 45° angles. Silkscreen is one opaque color. etc. These design assumptions lead to these tools being in the way more often than not for the increasing crowd of designers who try to create art with them.
Gerbolyze solves this problem. Gerbolyze interfaces with circuit board design tools such as Altium or Kicad on one side through standard Gerber files. It interfaces with vector graphics editors such as inkscape on the other side through Scaleable Vector Graphics (SVG) files. By fusing both, it yields a powerful environment for artistic circuit board design.
Gerbolyze Algorithm Overview
Gerbolyze has two major components. The first is the gerbolyze executable itself, which orchestrates the process of fusing SVG and Gerber files. The second is svg-flatten, a tool encapsulating all of the heavy-duty computer graphics code. The gerbolyze executable is a python script for readability, while the geometry backend is a C++ binary for performance.
In the beginning of the fusing process, the orchestrator figures out what semantic layers such as silkscreen or copper the tool's input files correspond to. The assigned layers are then processed one by one. For each layer, the tool first checks the input SVG file for any content. If there is none on this layer, the layer file is directly copied to the output. If ther is some, this SVG content is passed through the geometry backend to convert it to Gerber code. The resulting Gerber code is then read and added on top of the input file's gerber code. The result is written to the output.
The Computer Geometry of Scaleable Vector Graphics
The heavy lifting during this process is done by the geometry backend. While its job seems simple at first, it is surprisingly stretching the state of the art in both academic research and technical implementations of computer graphics. In its core the problem is that while SVG and Gerber are both essentially vector graphics formats, both have very different conceptions of their drawing models: They differ significantly in what happens when one of the input file's vectors is drawn.
SVG is little more than a highly standardized description of the basic operations provided by the modern 2D graphics interfaces such as Qt, Cairo or Skia that are built-in to all operating systems. Drawing paths that are described by the vector coördinates of points along them is the most basic of these operations. SVG also includes support for a surprising number of decidedly raster operations such as masking but, operating on grayscales, these are less relevant for the type of design one would create when targeting circuit board production processes.
Similar to SVG, the Gerber file format also targets a type of graphics programming interface. Only instead of that of operating systems 2D graphics APIs of the 90ies and 2000s, the Gerber format was created as a way to encapsulate commands for photoplotters, computer-controlled machines that physically move a light source across a photo-sensitive material. Gerber's concept of "aptertures" goes back to mechanical photoplotters having magazines of stencils of different shapes and sizes that could be swapped into the path of light during the plotting process.
Like SVG has its paths, the Gerber format has polygons. Polygons were added to the format to ease the description of irregularly-shaped areas: Previously, these would have to be drawn by overlaying thousands of thin lines, described one by one in the Gerber file. Using a Polygon, one only needs to describe the shape's outline as a series of points and the photoplotter will fill in the rest.
Transforming Vectors into Vectors
The crux in converting from SVG to Gerber lies here, in the conversion of paths. While in both a path or polygon is described by its outline, which is described by points, there are significant differences in the limitations both place on these outlines. In SVG an outline can consist of several types of segments: besides basic straight lines, multiple types of parametrized curves including cubic bezier curves are possible. An SVG path's outline can self-intersect (cross over itself). The path can also have holes, additional parts that are inside the outline.
Gerber, on the other hand, has a much more limited view of what a polygon is. In gerber, a polygon is something bounded by straight line segments, that cannot touch except under very particular circumstances, and holes are simply not supported. Converting from SVG's flexible model of a path to Gerber's very limited model of a polygon while preserving the fidelity of the input data is the true challenge here. As an aside, a fun complication one will encounter when embarking on this endeavour is that most programs that display Gerber files use modern graphics libraries in the backend. In these programs, a valid SVG path ineptly converted into an illegal gerber polygon may still end up looking alright since these programs usually just pass through the gerber's input data to the underlying graphics layer without validation—and that graphics layer is the one from SVG.
Styles and Strokes
Gerbolyze Image Vectorization
