It’s Springtime in the Quagg Garden, and several hummingbirds have declared it their own exclusive territory. When I take my lunch, I am greeted by spectacular aerial displays: both mating rituals and territorial defense. Less dramatic and yet equally (sonically) expressive, the mocking birds seem to be nesting nearby. Plenty of finches and bushtits and crows come by too.
As mentioned in Part 1, the purpose of this code is to help automate file format conversions and presentation for posting vector designs to Etsy. One kind of design I make is “shadow theaters,” which are essentially little layered dioramas that look nice when backlit.
The individual layers of these designs comprise an outline, scoring lines for folding the paper, and the design itself. However, creating a thumbnail to represent the design has a unique challenge: the layers are negatives. The design file fills the areas that will be cut out, but this is where the greatest illumination will come through. I want the thumbnail to look like the photograph above. Furthermore, I can’t simply composite all the layers, as they are opaque, and the result would only show the top layer.
So the task becomes to invert the layers. But even that isn’t so simple. In each of the layers, I want to take the filled area and make it transparent, and take the unfilled area and fill it. To really make it work, the filled areas should not be a uniform color, but should vary by how far “down” in the stack the layer is.
However, this isn’t as simple as removing layers like I did in Part 1. What I have to do is take the outermost layer, fill it, and subtract the geometry of the inner design from it. Fortunately, that’s not so difficult to do in SVG. If you take a path in SVG and close it, you can continue to add sub-paths. When those sub-paths are outside the original path, they are added to it. If the sub-paths are inside the original path, they are subtracted from it. If they overlap, they’re both added and subtracted. This is probably better explained with pictures.
Disclaimer: for the purpose of this discussion, I’m assuming two SVG settings: fill-rule and clip-rule are set to “evenodd”. There are other options, but they aren’t helpful for what I want to do.
What do these paths and sub-paths look like? If you look at the example from Part 1, you can see that a path has a d attribute, which is a string of commands and coordinates. Rather than go through those here, I’ll just link the relevant Mozilla SVG tutorial page which I found helpful. The key thing is that a complete, closed path ends with a Z command. Any path details after that are a subpath.
Looking at an SVG file of one of my shadow gallery layers, what I want to do is convert the “Design” layer to a fully-contained sub-path of the “PaperOutline” layer. Based on what we know of SVG paths, that means I can just append the design path to the outline path – the design path will become a sub-path which will be subtracted from the outline path! I then can set the fill color of this composite path, and I will effectively have filled the outline and subtracted my design.
I again take advantage of the fact that the layer names are following my standard. I search through the file for the “Design” layer, and copy its path into the $subtract_path variable. Then I loop through the groups again, find the “PaperOutline” layer, and append the path. While I’m at it, I set the fill color with a shade I calculate based on the layer number.
Not the most elegant code in the world, and will certainly fail on SVG files that don’t match my naming and layout conventions, but illustrates the process.
Once I’ve created these inverted SVGs, I convert them into PNGs, composite the stack into a single image, and come up with what I consider a handsome representation for my design thumbnail.
Once I have the ability to take layers and change the transparent areas and the fill color, I can do all sorts of other manipulations. For example, I can create striking negative images, or feed the the layers into other scripts to create “exploded” views of the shadow theaters.
To get people out to the polls, the numbers are pretty clear. Canvassing is the most effective technique to get people engaged. After that it’s not exactly clear whether texting, phone banking, or sending post-cards is next best.
But hey, Covid-19 means no canvassing right now. I hate telephones, so postcarding seems like a next-best approach. A lot of campaigns have their own systems set up, or you can contact Postcards to Voters and join up with their efforts.
You can get a lot of nice designs through a cooperation between Postcards to Voters and My Postcards. I wanted to come up with a few designs of my own. The individual files can be sent to a printing service and printed on 4″x6″ postcards, or you can download the combined version where they were squished to fit on a single sheet if you want to try printing them yourself.
Click on any of the images below to download a 300dpi PDF version.