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Improve cluster construction performance (#5584)

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<!-- Enter a brief description/summary of your PR here. What does it fix/what does it change/how was it tested (even manually, if necessary)? -->
## Summary of the Pull Request

A tiny performance fix in `renderer.cpp`.

<!-- Other than the issue solved, is this relevant to any other issues/existing PRs? --> 
## References

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## PR Checklist
* [ ] Closes #xxx
* [X] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [ ] Tests added/passed
* [ ] Requires documentation to be updated
* [ ] 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: #xxx

<!-- Provide a more detailed description of the PR, other things fixed or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

The cluster construction code is intensively called during rendering. Even though a single `back()` is fast, but accumulated `back()`s still take a noticiable amount of CPU cycles.


Before:

![perf1](https://user-images.githubusercontent.com/4710575/80323322-4342aa80-885d-11ea-92fb-06998dcef327.png)

After:

![图片](https://user-images.githubusercontent.com/4710575/80323336-52c1f380-885d-11ea-8244-4d8d432f7c52.png)

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## Validation Steps Performed

Manually validated.
This commit is contained in:
Chester Liu 2020-04-28 23:41:44 +08:00 committed by GitHub
parent d6cae40d26
commit 97d6456476
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GPG key ID: 4AEE18F83AFDEB23
1 changed files with 6 additions and 3 deletions
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9
src/renderer/base/renderer.cpp
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@ -730,6 +730,8 @@ void Renderer::_PaintBufferOutputHelper(_In_ IRenderEngine* const pEngine,
}
// Walk through the text data and turn it into rendering clusters.
// Keep the columnCount as we go to improve performance over digging it out of the vector at the end.
size_t columnCount = 0;
// If we're on the first cluster to be added and it's marked as "trailing"
// (a.k.a. the right half of a two column character), then we need some special handling.
@ -743,7 +745,8 @@ void Renderer::_PaintBufferOutputHelper(_In_ IRenderEngine* const pEngine,
// And tell the next function to trim off the left half of it.
trimLeft = true;
// And add one to the number of columns we expect it to take as we insert it.
clusters.emplace_back(it->Chars(), it->Columns() + 1);
columnCount = it->Columns() + 1;
clusters.emplace_back(it->Chars(), columnCount);
}
else
{
@ -755,11 +758,11 @@ void Renderer::_PaintBufferOutputHelper(_In_ IRenderEngine* const pEngine,
// Otherwise if it's not a special case, just insert it as is.
else
{
clusters.emplace_back(it->Chars(), it->Columns());
columnCount = it->Columns();
clusters.emplace_back(it->Chars(), columnCount);
}
// Advance the cluster and column counts.
const auto columnCount = clusters.back().GetColumns();
it += columnCount > 0 ? columnCount : 1; // prevent infinite loop for no visible columns
cols += columnCount;