Fix origin-mode cursor positioning#6
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Pull request overview
Fixes DEC origin-mode cursor positioning semantics when a scroll region is active, aligning CUP/HVP, VPA, and DECSTBM behavior with expected VT/xterm semantics and adding regression tests to prevent future regressions.
Changes:
- Added a shared origin-mode row translation helper and applied it to
CUP/HVPandVPA. - Updated
DECSTBMhandling to home the cursor after setting the scroll region, and adjusted origin-mode enable/disable homing behavior. - Added regression tests covering origin-relative addressing and cursor homing with scroll regions; added a FIXES.md note describing the behavior.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.
| File | Description |
|---|---|
| src/XTerm.NET/InputHandler.cs | Implements origin-mode row translation and cursor homing changes for scroll regions and origin mode toggles. |
| src/XTerm.NET.Tests/InputHandlerTests.cs | Adds regression tests for origin-relative CUP/HVP, origin-relative VPA, and scroll-region cursor homing. |
| src/XTerm.NET.Tests/ModeHandlingTests.cs | Adds regression test ensuring enabling origin mode homes to the top margin when a scroll region is set. |
| FIXES.md | Documents the behavioral fixes and provides minimal reproductions and validation notes. |
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tomlm
approved these changes
Jun 21, 2026
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Summary
This fixes DEC origin-mode cursor positioning with scroll regions:
DECSTBM/CSI t;b rnow moves the cursor to home after setting the scroll region.CUP/HVP(CSI row;col H/f) now treat row coordinates as relative to the scroll region whenDECOM/ origin mode is enabled.VPA/CSI row dnow applies the same origin-mode row translation.Why
Terminal UIs that reserve a bottom prompt/status row commonly set a scroll region for the output area and use origin-relative cursor addressing. Without these semantics, content can be written to the wrong absolute rows and preserved into scrollback incorrectly.
This is a core emulator behavior fix only. It intentionally does not include any host-rendering, PTY, ConPTY, or Termrig-specific compatibility shims.
Validation
dotnet test src\XTerm.NET.slnx --no-restoreThe test run still reports the existing compiler warnings about
EscapeSequenceParser.DcsandTerminal.HyperlinkChanged; this PR did not introduce new warnings.