[czj]

Invoices carry a payment QR code, but drawing one took another gem that makes a PNG, plus glue code to size it, and a bitmap scans worse once scaled. This is the first part of #74; the linear codes and DataMatrix follow in their own pull requests.

qr_code encodes the text and draws it as vector rectangles: one path and one fill per symbol, with no dependency.

• The whole standard: versions 1 to 40, levels :l, :m, :q and :h, and numeric, alphanumeric and byte modes; UTF-8 text is announced by an ECI. The smallest version that holds the text is chosen, and text too long for any version raises.
• Sized for scanners: size is the symbol's width with its four-module quiet zone, or module_size sets one module (2 pt by default). quiet_zone: false and color are options too.
• Placed like images: at, or position and vposition, and the cursor moves past the code.
• Native API: qr_code is a box with size, module_size, level, quiet_zone, color and align.
• Read back in CI: CI installs zbar, which reads every test code from the rendered page; the README and AGENTS.md list it among the test tools.

Proof

test/qr_code_test.rb draws 9 texts at each of the 4 levels and reads them back with zbar from the page rendered at 150 dpi: a URL, digits, the alphanumeric set, UTF-8 with CJK, an empty string, and random ASCII up to 400 characters. A version 28 code of 1500 bytes reads back too. Version choice matches the standard's capacities: 41 digits fit version 1-L and 42 do not, 7089 digits, 4296 alphanumerics and 2953 bytes fit version 40-L, 1273 bytes fit 40-H and 1274 raise. One code is one fill, at the expected corner and width. Encoding a 37-character URL takes 5.7 ms without JIT, most of it spent scoring the 8 masks; a full version 40 code takes 0.22 s. rake test: 1354 runs, 0 failures; RuboCop is clean.

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Generated by Claude Code