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[PR #5758] Refactor the SGR implementation in AdaptDispatch #26464

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opened 2026-01-31 09:16:15 +00:00 by claunia · 0 comments
claunia commented 2026-01-31 09:16:15 +00:00
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Original Pull Request: https://github.com/microsoft/terminal/pull/5758

State: closed
Merged: Yes

Summary of the Pull Request

This is an attempt to simplify the SGR (Select Graphic Rendition) implementation in conhost, to cut down on the number of methods required in the ConGetSet interface, and pave the way for future improvements and bug fixes. It already fixes one bug that prevented SGR 0 from being correctly applied when combined with meta attributes.

References

  • This a first step towards fixing the conpty narrowing bugs in issue #2661
  • I'm hoping the simplification of ConGetSet will also help with #3849.
  • Some of the TextAttribute refactoring in this PR overlaps with similar work in PR #1978.

PR Checklist

Detailed Description of the Pull Request / Additional comments

The main point of this PR was to simplify the AdaptDispatch::SetGraphicsRendition implementation. So instead of having it call a half a dozen methods in the ConGetSet API, depending on what kinds of attributes needed to be set, there is now just one call to get current attributes, and another call to set the new value. All adjustments to the attributes are made in the AdaptDispatch class, in a simple switch statement.

To help with this refactoring, I also made some change to the TextAttribute class to make it easier to work with. This included adding a set of methods for setting (and getting) the individual attribute flags, instead of having the calling code being exposed to the internal attribute structures and messing with bit manipulation. I've tried to get rid of any methods that were directly setting legacy, meta, and extended attributes.

Other than the fix to the SGR 0 bug, the AdaptDispatch refactoring mostly follows the behaviour of the original code. In particular, it still maps the SGR 38/48 indexed colors to RGB instead of retaining the index, which is what we ultimately need it to do. Fixing that will first require the color tables to be unified (issue #1223), which I'm hoping to address in a followup PR.

But for now, mapping the indexed colors to RGB values required adding an an additional ConGetSet API to lookup the color table entries. In the future that won't be necessary, but the API will still be useful for other color reporting operations that we may want to support. I've made this API, and the existing setter, standardise on index values being in the "Xterm" order, since that'll be essential for unifying the code with the terminal adapter one day.

I should also point out one minor change to the SGR 38/48 behavior, which is that out-of-range RGB colors are now ignored rather than being clamped, since that matches the way Xterm works.

Validation Steps Performed

This refactoring has obviously required corresponding changes to the unit tests, but most were just minor updates to use the new TextAttribute methods without any real change in behavior. However, the adapter tests did require significant changes to accommodate the new ConGetSet API. The basic structure of the tests remain the same, but the simpler API has meant fewer values needed to be checked in each test case. I think they are all still covering the areas there were intended to, though, and they are all still passing.

Other than getting the unit tests to work, I've also done a bunch of manual testing of my own. I've made sure the color tests in Vttest all still work as well as they used to. And I've confirmed that the test case from issue #5341 is now working correctly.

**Original Pull Request:** https://github.com/microsoft/terminal/pull/5758 **State:** closed **Merged:** Yes --- ## Summary of the Pull Request This is an attempt to simplify the SGR (Select Graphic Rendition) implementation in conhost, to cut down on the number of methods required in the `ConGetSet` interface, and pave the way for future improvements and bug fixes. It already fixes one bug that prevented SGR 0 from being correctly applied when combined with meta attributes. ## References * This a first step towards fixing the conpty narrowing bugs in issue #2661 * I'm hoping the simplification of `ConGetSet` will also help with #3849. * Some of the `TextAttribute` refactoring in this PR overlaps with similar work in PR #1978. ## PR Checklist * [x] Closes #5341 * [x] CLA signed. * [x] Tests added/passed * [ ] Requires documentation to be updated * [x] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: https://github.com/microsoft/terminal/pull/3160#discussion_r341249386 ## Detailed Description of the Pull Request / Additional comments The main point of this PR was to simplify the `AdaptDispatch::SetGraphicsRendition` implementation. So instead of having it call a half a dozen methods in the `ConGetSet` API, depending on what kinds of attributes needed to be set, there is now just one call to get current attributes, and another call to set the new value. All adjustments to the attributes are made in the `AdaptDispatch` class, in a simple switch statement. To help with this refactoring, I also made some change to the `TextAttribute` class to make it easier to work with. This included adding a set of methods for setting (and getting) the individual attribute flags, instead of having the calling code being exposed to the internal attribute structures and messing with bit manipulation. I've tried to get rid of any methods that were directly setting legacy, meta, and extended attributes. Other than the fix to the `SGR 0` bug, the `AdaptDispatch` refactoring mostly follows the behaviour of the original code. In particular, it still maps the `SGR 38/48` indexed colors to RGB instead of retaining the index, which is what we ultimately need it to do. Fixing that will first require the color tables to be unified (issue #1223), which I'm hoping to address in a followup PR. But for now, mapping the indexed colors to RGB values required adding an an additional `ConGetSet` API to lookup the color table entries. In the future that won't be necessary, but the API will still be useful for other color reporting operations that we may want to support. I've made this API, and the existing setter, standardise on index values being in the "Xterm" order, since that'll be essential for unifying the code with the terminal adapter one day. I should also point out one minor change to the `SGR 38/48` behavior, which is that out-of-range RGB colors are now ignored rather than being clamped, since that matches the way Xterm works. ## Validation Steps Performed This refactoring has obviously required corresponding changes to the unit tests, but most were just minor updates to use the new `TextAttribute` methods without any real change in behavior. However, the adapter tests did require significant changes to accommodate the new `ConGetSet` API. The basic structure of the tests remain the same, but the simpler API has meant fewer values needed to be checked in each test case. I think they are all still covering the areas there were intended to, though, and they are all still passing. Other than getting the unit tests to work, I've also done a bunch of manual testing of my own. I've made sure the color tests in Vttest all still work as well as they used to. And I've confirmed that the test case from issue #5341 is now working correctly.
claunia added the pull-request label 2026-01-31 09:16:15 +00:00
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Reference: starred/terminal#26464
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