Pass through soft fonts over conpty #13965
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This is so clever! I'm excited to review it. Thanks! |
src/renderer/vt/paint.cpp
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| // Write the actual text string. If we're using a soft font, the character | ||
| // set should have already been selected, so we just need to map our internal | ||
| // representation back to ASCII (handled by the _WriteTerminalDrcs method). | ||
| if (_usingSoftFont) |
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| if (_usingSoftFont) | |
| if (_usingSoftFont) [[unlikely]] |
@lhecker is this the correct usage of that annotation in C++?
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Yeah that would work. likely/unlikely aren't particularly impactful in MSVC right now, but it does influence the inalienability of functions quite a bit, which can help make our binaries more compact.
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I've just tried this, and it does make a bit of a difference. Both of the _WriteTerminalXXX calls are inline, so there is quite a lot of code in the two branches of that condition. With the unlikely attribute added, part of the first branch gets pulled out of the main body of code, so there is a slightly shorter jump to the else branch.
I don't know if that's really worth the effort, though. I think if you wanted to make a significant difference with these attributes, a good place to put them might be in the RETURN_IF_FAILED macros. That should remove all that diagnostic logging from the main path of execution which is probably quite a chunk of code.
I'm not an optimization expert though, so I'll leave it to you guys to decide.
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Only saw Leonard's reply after I posted mine. I've applied the suggested change now.
Apply [[unlikely]] attribute to less used branch. Co-authored-by: Dustin L. Howett <dustin@howett.net>
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This PR introduces a mechanism for passing through downloadable soft
fonts to the conpty client, so that we can support DRCS (Dynamically
Redefinable Character Sets) in Windows Terminal.
Soft fonts were first implemented in conhost (with the GDI renderer) in
PR #10011, and were implemented in the DX renderer in PR #13362.
The way this works is by passing through the
DECDLDsequencecontaining the font definition, but with the character set ID patched to
use a hardcoded value (this is to make sure it's not going to override
the default character set). At the same time we send through an
SCSsequence to map this character set into the G1 table so we can easily
activate it.
We still need to process the
DECDLDsequence locally, though, sincethe initial character set mapping take place on the host side. This gets
the DRCS characters into our buffer as PUA Unicode characters. Then when
the VT engine needs to output these characters, it masks them with
7Fto map them back to ASCII, and outputs an
SOcontrol to activate thesoft font in the conpty client.
Validation Steps Performed
I've manually tested with a number of soft fonts and applications that
make use of soft fonts. But if you're testing with the VT320 fonts from
the vt100.net collection, note that you'll need to enable the ISO-2022
coding system first, since they use 8-bit C1 controls.