QR codes

Qr:
  x: 2
  y: 2
  size: 6
  data: [code]

data: is a text expression, so the code can come straight from a sheet column (data: [code]), be interpolated (data: "https://example.com/[code]"), or be computed with a conditional — the usual coercions apply.

The idiom: one QR per card, on the back#

The point of a card's QR is usually to let a companion app scan it and act — a cross-media game where the app is out of scope for CardGoblin, but the code on the card is exactly what it needs. Because Back: templates evaluate per card just like Front: templates (every card sees its own row's data), a Back: template needs nothing extra to give every card in the deck a different code:

Qr:
  x: 2
  y: 2
  size: 16
  data: [code]

Those four lines — x y size data — are the whole idiom: a Text column of codes in your sheet, one Qr: block in a Back: template, and every card's back carries its own scannable code.

level: — error correction#

QR codes carry redundant data on purpose, so a code still scans even partly obscured, scratched, or printed small. level: picks how much:

A higher level may need a bigger code for larger payloads (more of the code's capacity goes to redundancy instead of your content, so less room is left for data: at a given size) — a short code (a plain URL, a short id) is often the same size at every level, but the difference shows up once the content pushes against a level's capacity. Worth raising for a code that'll be printed small or handled roughly, and safe to leave at the default otherwise.

The quiet zone lives inside the box#

Every QR code needs a plain border — the quiet zone — around the modules for a scanner to find it. size: is the side of the box you declare, and the quiet zone is drawn inside it, in background:, so an adjacent shape can never crowd a code's scan margin just by sitting close on the card. The box you draw is exactly the box a scanner sees.

When the data doesn't fit#

Every QR code has a capacity ceiling, set by level: (higher levels hold less content at a given size) — a code has a limit past which no code can be built at all, no matter how large. data: that exceeds it is a QR data is too long for one code error, and the card renders as a placeholder, the same "this one card's data was the problem" isolation every other data-time error gets — the rest of the deck is unaffected. An empty data: is not this case: it encodes as a normal, valid, tiny code — there's nothing special about zero-length data.