Each jigsaw is designed and developed entirely in the browser. Above are some random outputs generated on the fly just for you – crack open the explorer for finer control of the parameters.
The strokes are packed tightly together at a low opacity, making sweeping, feathery fans. In high density areas the strokes blend together to create a painterly effect, but in emptier areas the shape of the spines is made clear.
This was the closest to a gradient puzzle I've made so far - where the main strategy of solving it was to find the brightest / darkest / pinkest / bluest pieces and place them in order; I find this type of design much less engaging than having also to consider the texture, orientation, or composition of pieces to put them together.