Add support for line renditions in the DX renderer #13102
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This PR introduces a mechanism for passing through line rendition attributes to the conpty client, so we can support double-width and double-height text in Windows Terminal. Line renditions were first implemented in conhost (with the GDI renderer) in PR #8664, and were implemented in the DX renderer in PR #13102. By default this won't add any additional overhead to the conpty output, but as soon as there is any usage of double-size text, we switch to a mode in which every line output will be prefixed with a line rendition sequence. This is to ensure that the line attributes in the client terminal are always in sync with the host. Since this does add some overhead to the conpty output, we'd prefer not to remain in this mode longer than necessary. So whenever there is a full repaint of the entire viewport, we check to see if all of the lines are single-width. If that is the case, we can then safely skip the line rendition sequences in future updates. One other small optimization is when the conpty update is only writing out a single character (this is something we already check for). When that is the case, we can safely skip the line rendition prefix, because a single character update should never include a change of the line rendition. ## Validation Steps Performed I've manually tested that Windows Terminal now passes the double-size tests in _Vttest_, and also confirmed various edge cases are working correctly in my own double-size tests. Closes #11595
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This PR adds support for the VT line rendition attributes in the DirectX
renderer, which allows for double-width and double-height line
renditions.
Line renditions were first implemented in conhost (with the GDI
renderer) in PR #8664. Supporting them in the DX renderer now is a
small step towards #11595.
The DX implementation is very similar to the GDI one. When a particular
line rendition is requested, we create a transform that is applied to
the render target. And in the case of double-height renditions, we also
initialize some clipping offsets to allow for the fact that we only
render half of a line at a time.
One additional complication exists when drawing the cursor, which
requires a two part process where it first renders to a command list,
and then draw the command list in a second step. We need to temporarily
reset the transform in that first stage otherwise it ends up being
applied twice.
I've manually tested the renderer in conhost by setting the
UseDxregistry entry and confirmed that it passes the Vttest double-size
tests as well as several of my own tests. I've also checked that the
renderer can now handle horizontal scrolling, which is a feature we get
for free with the transforms.