Don't allow a linefeed to scroll when outside DECSTBM margins #3704
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miniksa
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Dec 11, 2019
DHowett-MSFT
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Summary of the Pull Request
When the
DECSTBMmargins are set, scrolling should only allowed withinthose margins. So if the cursor is below the bottom margin, it should
just be clamped when it tries to move down from the bottom line of the
viewport, instead of scrolling the screen up. This PR implements that
restriction, i.e. it prevents scrolling taking place outside the
DECSTBMmargins, which was previously allowed.PR Checklist
Detailed Description of the Pull Request / Additional comments
This simply adds a condition in the
AdjustCursorPositionfunction tocheck if the cursor is moving below the bottom of the viewport when the
margins are set. If so, it clamps the y coordinate to the bottom line of
the viewport.
The only time it's acceptable for scrolling to happen when margins are
set, is if the scrolling is taking place within those margins. But those
cases would already have been handled earlier in the function (in the
fScrollDownorscrollDownAtTopconditions), and thus the ycoordinate would have already been prevented from moving out of the
viewport.
Validation Steps Performed
I've added some screen buffer tests to confirm this new behaviour, and
I've also checked the test case from the initial bug report (#2657) and
made sure it now matches the results in XTerm.