terminal/osc: accept iTerm2 OSC 1337 ReportCellSize query#379
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iTerm2 emitters like imgcat can query the cell pixel size with `OSC 1337;ReportCellSize ST`. The terminal replies with `OSC 1337;ReportCellSize=H;W;1.0 ST` carrying the cell dimensions in backing pixels (scale=1.0 so clients computing H*scale get the value they need without DPR plumbing). The dispatch reuses the existing size-report Action so that libghostty-vt embedders implementing reportSize get the response for free, mirroring csi_21_t which is similarly OSC-driven. Trailing `=` with an empty value is accepted defensively to match the FileEnd path's tolerance for naive `key=value` emitters; any `=non-empty` form is rejected because it would collide with the response shape.
Add the matching GHOSTTY_SIZE_REPORT_ITERM2_REPORT_CELL_SIZE entry to the C header so the libghostty-vt ABI mirrors the Zig enum, and tighten a few comments to ground them in the actual mechanism (key=value split producing an empty value, backing pixels instead of "logical pixels on retina").
This was referenced May 19, 2026
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iTerm2 emitters like imgcat can query the cell pixel size with `OSC 1337;ReportCellSize ST`. The terminal replies with `OSC 1337;ReportCellSize=H;W;1.0 ST` carrying the cell dimensions in backing pixels (scale=1.0 so clients computing H*scale get the value they need without DPR plumbing). The dispatch reuses the existing size-report Action so that libghostty-vt embedders implementing reportSize get the response for free, mirroring csi_21_t which is similarly OSC-driven. The libghostty-vt C ABI gains a matching GHOSTTY_SIZE_REPORT_ITERM2_REPORT_CELL_SIZE entry. Trailing `=` with an empty value is accepted defensively because the upstream key=value split produces an empty value for such input; any `=non-empty` form is rejected because it would collide with the response shape.
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Summary
Accept iTerm2's
OSC 1337;ReportCellSizebare-key query and reply with the cell pixel size on the pty. Sixth PR in the iTerm2 OSC 1337 series (after #375 #376 #377 #378), and the smallest by design.Emitters like
imgcatuse this to compute image-cell scaling. With the prior PRs we accept and render inline images; this PR closes the loop so clients can ask the terminal "how big is a cell?" before sending an image.Wire format
\x1b]1337;ReportCellSize\x1b\(bare key)\x1b]1337;ReportCellSize={cell_height};{cell_width};1.0\x1b\The trailing
1.0is iTerm2's HiDPI scale field. Ghostty reports cell metrics already in backing pixels, soscale=1.0lets clients computeH * scale = backing_pixelswithout us threading device-pixel ratio through the size-report pipeline. Clients that parse the legacy two-field form ignore the trailing scale.Architecture
Reuses the existing
size_report.Actiondispatch:iterm2_report_cell_sizevariant oncsi.SizeReportStyle(alongsidecsi_21_twhich is similarly OSC-driven, so this is not a new pattern)iterm2_report_cell_sizevariant onsize_report.Style(encoder-side enum) and an encoder branchparsers/iterm2.zigemittingCommand.iterm2_report_cell_size(void).size_reportwith the new stylesendSizeReport(termio) andreportSize(libghostty-vt embedders) both pick up the new variant through their existing switchesResult: libghostty-vt embedders that implement
effects.sizeget the ReportCellSize response without any C-side or apprt-side work.Parser permissiveness
ReportCellSize-> emit queryReportCellSize=-> emit query (defensive, matchesFileEnd=precedent)ReportCellSize=non-empty-> reject (would collide with the response shape)Tests
=empty value accepted,=non-emptyrejectedTest plan
zig build testpasses on Windowszig build testpasses on macOS (via SSH bundle)imgcatonce we have a Wintty.exe build