Update the virtual bottom location if the cursor moves below it #5317
Conversation
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
|
I'm not absolutely certain that this is the right solution, but if you're looking for a quick fix for #5302, this is at least one option. |
zadjii-msft
requested changes
Apr 10, 2020
ghost
added
the
Needs-Author-Feedback
miniksa
approved these changes
Apr 10, 2020
There was a problem hiding this comment.
Am hitting approve as I think this is decent and @zadjii-msft is already holding the block for a test.
ghost
removed
the
Needs-Author-Feedback
j4james
force-pushed
the
fix-virtual-bottom
branch
from
2bd027a
to
6b8fac1
Compare
Yeah I figured you'd probably want a unit test for this - I just wasn't exactly sure how I would do it. But I think I've now got something that is a reasonable approximation of the original bug report (6b8fac1). |
DHowett-MSFT
approved these changes
Apr 13, 2020
zadjii-msft
approved these changes
Apr 14, 2020
DHowett-MSFT
changed the title
ghost
pushed a commit
that referenced
this pull request
May 2, 2022
The "virtual bottom" marks the last line of the mutable viewport area, which is the part of the buffer that VT sequences can write to. This region should typically only move downwards as new lines are added to the buffer, but there were a number of cases where it was incorrectly being moved up, or moved down further than necessary. This PR attempts to fix that. There was an earlier, unsuccessful attempt to fix this in PR #9770 which was later reverted (issue #9872 was the reason it had to be reverted). PRs #2666, #2705, and #5317 were fixes for related virtual viewport problems, some of which have either been extended or superseded by this PR. `SetConsoleCursorPositionImpl` is one of the cases that actually does need to move the virtual viewport upwards sometimes, in particular when the cmd shell resets the buffer with a `CLS` command. But when this operation "snaps" the viewport to the location of the cursor, it needs to use the virtual viewport as the frame of reference. This was partially addressed by PR #2705, but that only applied in terminal-scrolling mode, so I've now applied that fix regardless of the mode. `SetViewportOrigin` takes a flag which determines whether it will also move the virtual bottom to match the visible viewport. In some case this is appropriate (`SetConsoleCursorPositionImpl` being one example), but in other cases (e.g. when panning the viewport downwards in the `AdjustCursorPosition` function), it should only be allowed to move downwards. We can't just not set the update flag in those cases, because that also determines whether or not the viewport would be clamped, and we don't want change that. So what I've done is limit `SetViewportOrigin` to only move the virtual bottom downwards, and added an explicit `UpdateBottom` call in those places that may also require upward movement. `ResizeWindow` in the `ConhostInternalGetSet` class has a similar problem to `SetConsoleCursorPositionImpl`, in that it's updating the viewport to account for the new size, but if that visible viewport is scrolled back or forward, it would end up placing the virtual viewport in the wrong place. So again the solution here was to use the virtual viewport as the frame of reference for the position. However, if the viewport is being shrunk, this can still result in the cursor falling below the bottom, so we need an additional check to adjust for that. This can't be applied in pty mode, though, because that would break the conpty resizing operation. `_InternalSetViewportSize` comes into play when resizing the window manually, and again the viewport after the resize can end up truncating the virtual bottom if not handled correctly. This was partially addressed in the original code by clamping the new viewport above the virtual bottom under certain conditions, and only in terminal scrolling mode. I've replaced that with a new algorithm which links the virtual bottom to the visible viewport bottom if the two intersect, but otherwise leaves it unchanged. This applies regardless of the scrolling mode. `ResizeWithReflow` is another sizing operation that can affect the virtual bottom. This occurs when a change of the window width requires the buffer to be reflowed, and we need to reposition the viewport in the newly generated buffer. Previously we were just setting the virtual bottom to align with the new visible viewport, but that could easily result in the buffer truncation if the visible viewport was scrolled back at the time. We now set the virtual bottom to the last non-space row, or the cursor row (whichever is larger). There'll be edge cases where this is probably not ideal, but it should still work reasonably well. `MakeCursorVisible` was another case where the virtual bottom was being updated (when requested with a flag) via a `SetViewportOrigin` call. When I checked all the places it was used, though, none of them actually required that behavior, and doing so could result in the virtual bottom being incorrectly positioned, even after `SetViewportOrigin` was limited to moving the virtual bottom downwards. So I've now made it so that `MakeCursorVisible` never updates the virtual bottom. `SelectAll` in the `Selection` class was a similar case. It was calling `SetViewportOrigin` with the `updateBottom` flag set when that really wasn't necessary and could result in the virtual bottom being incorrectly set. I've changed the flag to false now. ## Validation Steps Performed I've manually confirmed that the test cases in issue #9754 are working now, except for the one involving margins, which is bigger problem with `AdjustCursorPosition` which will need to be addressed separately. I've also double checked the test cases from several other virtual bottom issues (#1206, #1222, #5302, and #9872), and confirmed that they're still working correctly with these changes. And I've added a few screen buffer tests in which I've tried to cover as many of the problematic code paths as possible. Closes #9754
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Summary of the Pull Request
If an application writes to the screen while not in VT mode, and the user has scrolled forward in the screen buffer, the virtual bottom location is not updated to take that new content into account. As a result, the viewport can later jump back to the previous virtual bottom, making the content disappear off screen. This PR attempts to fix that issue by updating the virtual bottom location whenever the cursor moves below that point.
PR Checklist
Detailed Description of the Pull Request / Additional comments
This simply adds a condition in the
SCREEN_INFORMATION::SetCursorPositionto check if the new Y coordinate is below the current virtual bottom, and if so, updates the virtual bottom to that new value.I considered trying to make it only update when something is actually written to the screen, but this seemed like a cleaner solution, and is less likely to miss out on a needed update.
Validation Steps Performed
I've manually tested the case described in issue #5302, and confirmed that it now works as expected. I've also added a unit test that checks the virtual bottom is updated correctly under similar conditions.