0.10.7 — an image variant

Image services can be particular about the shape of a frame. One of them accepts proportions from a narrow band and does no cropping of its own: a photograph outside the range simply does not go in, and the automation receives an error instead of a published post. In a feed where horizontal frames, vertical ones and generated quote cards stand side by side, sooner or later a frame turns up that the recipient will not take.

Cropping on the fly was out from the start. A photograph in a picture series is composed deliberately, and trimming it to someone else's format takes away precisely what it was made for. Instead there is a variant: the whole photograph fitted into a vertical canvas, filled out with the same ground as the preview cards. Nothing is lost, the format is the same for every entry, and a quote card blends into the canvas without a visible seam, because the ground is the same shade.

So the feed takes a second parameter, alongside the source marker. It was tempting to fold this into the marker — if an image service is reading, then it is obvious which files it wants. But these are two different things: the marker says WHO reads the feed, the variant says WHICH file is needed. Usually they travel together, not always: two services can want the same frame under different markers, and one service two frames in two scenarios. Glued together once, they come apart painfully later.

The basis for a variant is the full-resolution photograph, and where an entry has none, the quote card that every entry carries, text-only ones included. No entry drops out of the feed for want of a picture.

One thing remains that the engine will not do for anyone. The feed publishes the variant's address without checking whether the file exists — execution at the edge of the network cannot see a disk. A missing file is a four-oh-four and a post that does not go out. The tool that generates variants therefore has a checking mode: it walks the image directory and lists everything without a counterpart. That is the only sensible answer to a check that cannot be made where it hurts.