photocraft/docs/printing.md

Printing

File › Print renders the flattened document onto one PDF page (paper size and orientation, position and scale, crop and registration marks, labels, colour handling) and hands that page to a printer. The rendering is print_cmds.rs in photocraft-engine, shared by the dialog, the batch commands and automation (file.print, file.printOneCopy); this page is about the hand-off.

Positioning the preview

Drag the visible image on the paper to change Top and Left. Starting a drag switches Center off using the currently resolved layout, including Scale to Fit Media, so the image stays at the grab point. Top/Left stay visible but disabled while Center is on, keeping the dialog and paper stationary when a drag enables them. Position fields accept negative values in inches, centimetres or millimetres; the stored command parameters are inches from the sheet's top-left. Manual positions are bounded to ±10000 inches. Height, width and paper dimensions retain their positive fields.

The preview converts egui point displacement to PDF points using its paper display scale. No extra Retina pixel factor is needed: painting and pointer input both use egui points. Emulsion Down reverses the horizontal position change to match the mirrored output. The image is clipped to the paper; any visible portion remains a drag target. A completely off-page image can be recovered with Top/Left or Center. These controls affect print parameters only, and the preview and generated PDF continue to share print_cmds::layout.

Routes to the printer

Route	When	What the user sees
craft-print (lp on CUPS, the Windows spooler)	lp is on the path (macOS, Linux, the Flatpak, which bundles it) and CUPS lists a printer, or on Windows	Sent to the printer (request id is Office-42)
CUPS over IPP (photocraft-ipp)	No lp on the path and a print server answers: CUPS_SERVER, then /run/cups/cups.sock, /var/run/cups/cups.sock, /private/var/run/cupsd, then localhost:631; always for a printServer named in the request	Sent to the printer (job 42 on Office)
Print portal (org.freedesktop.portal.Print, desktop app on Linux)	Linux only (the Flatpak included): no print server reachable or no printer set up (including when lp is there but CUPS lists no printer and none was named), or always with PHOTOCRAFT_PRINT_PORTAL=1. Elsewhere a missing route is an error	The system print dialog, seeded with the copies and paper; the outcome goes to the log
Print to PDF	output given (the Output field of the dialog)	The file; nothing is spooled unless send is true

A route that exists but fails (an unknown printer, a job the queue refuses) is an error; only a missing route (no lp, no print server, no printer) moves on to the next one. With no printer named and no default, the only printer takes the job on the lp and IPP routes; Windows needs a named or default printer.

The IPP client is in-process, pure Rust (RFC 8010/8011: CUPS-Get-Printers, CUPS-Get-Classes, CUPS-Get-Default, Print-Job with the PDF as the document), so no lp binary is needed. It only sees queues the server has, not driverless network printers, which is why the Flatpak bundles lp/lpstat (the manifest's cups-client module) and grants --socket=cups (the host's CUPS socket) and org.freedesktop.Avahi (lpstat -e finds driverless printers). On a system without CUPS, or in a sandbox without the socket, the app falls back to the print portal, whose dialog runs outside the sandbox.

Which printer

The dialog's Printer field, or "printer" in the command, names a queue (case-insensitively; a CUPS class counts, as with lp -d). Left empty, the server's default printer is used; without a default, the only printer; with several and no default, the error names them. With no printer at all, the portal takes over when it is available, otherwise the error says to add one in the system settings or print to PDF.

file.printers lists what the print server knows: {"printServer": "host[:port]|socket"} is optional and defaults to the system's CUPS; the result is {server, default, printers: [{name, info, state, acceptingJobs, default, class}]}, or an empty list with a note when no server answers. "printServer" on file.print sends one job to a named server; "dryRun": true renders the page and reports the equivalent lp command without spooling.

Orientation (Windows)

On Windows the paper and its orientation are the driver's: the Print dialog takes them from the printer's settings. Its Orientation buttons (Portrait, Landscape; Photoshop's Layout) turn those settings, as Print Settings… would, and the paper and preview turn with them. file.print.page {"orientation": "portrait|landscape"} does the same for scripts: it returns the turned settings as printerSettings, with the page they give. A print sent to a Windows printer whose layout is the driver's paper the other way round (a landscape layout, portrait settings) turns the settings to the layout before printing, rather than stopping with "the driver paper or orientation differs"; another paper is still refused.

Scale to Fit Media fills the printable area the driver reports for that page (printable in file.print.page), so borderless paper prints edge to edge (#7782). The area turns with the paper, and a print sent to a Windows printer reads it from the driver itself. Without a driver page (CUPS, IPP, a PDF or a preview) it fits the paper less an 18 pt margin, as before.

Results

file.print returns sent, backend (lp, windows, ipp, portal), spooler (where the job went) and pdf (the page's path, only when output named one).

Environment

Variable	Effect
CUPS_SERVER	The print server, as CUPS itself reads it: host[:port] or a socket path
PHOTOCRAFT_PRINT_PORTAL=1	Always use the system print dialog (the portal) instead of lp or CUPS directly
PHOTOCRAFT_PRINT_PORTAL=0	Never use the portal; a missing print server is then an error

Verification

• crates/ipp/src/tests.rs: the client against a fake CUPS over TCP and a Unix socket: printer listing with state and default, the default printer and its absence, Print-Job with the document and the job id, chunked and content-length replies, HTTP and IPP error statuses, broken replies.
• crates/engine/src/print_cmds/tests.rs: printer resolution (requested, default, only one, several without a default, unknown, none); a complete file.print against a fake CUPS (printer URI, copies, job name, document format, the PDF itself) and file.printers; lp taking the job when it is on the path; the IPP route when it is not (a child process with an empty path); the app's spooler when preferred, as the fallback without a printer, and skipped when a server is named; print to PDF untouched.
• apps/photocraft/src/print_portal.rs: the request path rule and the paper/copies seeding of the dialog (PWG names for the standard papers, millimetres for custom sizes).