## Summary of the Pull Request
Identifies and scales glyphs in the box and line drawing ranges U+2500-U+259F to fit their cells.
## PR Checklist
* [x] Closes#455
* [x] I work here.
* [x] Manual tests. This is all graphical.
* [x] Metric ton of comments
* [x] Math spreadsheet included in PR.
* [x] Double check RTL glyphs.
* [x] Why is there the extra pixel?
* [x] Scrolling the mouse wheel check is done.
* [x] Not drawing outline?
* [x] Am core contributor. Roar.
* [x] Try suppressing negative scale factors and see if that gets rid of weird shading.
## Detailed Description of the Pull Request / Additional comments
### Background
- We want the Terminal to be fast at drawing. To be fast at drawing, we perform differential drawing, or only drawing what is different from the previous frame. We use DXGI's `Present1` method to help us with this as it helps us compose only the deltas onto the previous frame at drawing time and assists us in scrolling regions from the previous frame without intervention. However, it only works on strictly integer pixel row heights.
- Most of the hit testing and size-calculation logic in both the `conhost` and the Terminal products are based on the size of an individual cell. Historically, a cell was always dictated in a `COORD` structure, or two `SHORT` values... which are integers. As such, when we specify the space for any individual glyph to be displayed inside our terminal drawing region, we want it to fall perfectly inside of an integer box to ensure all these other algorithms work correctly and continue to do so.
- Finally, we want the Terminal to have font fallback and locate glyphs that aren't in the primary selected font from any other font it can find on the system that contains the glyph, per DirectWrite's font fallback mechanisms. These glyphs won't necessarily have the same font or glyph metrics as the base font, but we need them to fit inside the same cell dimensions as if they did because the hit testing and other algorithms aren't aware of which particular font is sourcing each glyph, just the dimensions of the bounding box per cell.
### How does Terminal deal with this?
- When we select a font, we perform some calculations using the design metrics of the font and glyphs to determine how we could fit them inside a cell with integer dimensions. Our process here is that we take the requested font size (which is generally a proxy for height), find the matching glyph width for that height then round it to an integer. We back convert from that now integer width to a height value which is almost certainly now a floating point number. But because we need an integer box value, we add line padding above and below the glyphs to ensure that the height is an integer as well as the width. Finally, we don't add the padding strictly equally. We attempt to align the English baseline of the glyph box directly onto an integer pixel multiple so most characters sit crisply on a line when displayed.
- Note that fonts and their glyphs have a prescribed baseline, line gap, and advance values. We use those as guidelines to get us started, but then to meet our requirements, we pad out from those. This results in fonts that should be properly authored showing gaps. It also results in fonts that are improperly authored looking even worse than they normally would.
### Now how does block and line drawing come in?
- Block and Line drawing glyphs are generally authored so they will look fine when the font and glyph metrics are followed exactly as prescribed by the font. (For some fonts, this still isn't true and we want them to look fine anyway.)
- When we add additional padding or rounding to make glyphs fit inside of a cell, we can be adding more space than was prescribed around these glyphs. This can cause a gap to be visible.
- Additionally, when we move things like baselines to land on a perfect integer pixel, we may be drawing a glyph lower in the bounding box than was prescribed originally.
### And how do we solve it?
- We identify all glyphs in the line and block drawing ranges.
- We find the bounding boxes of both the cell and the glyph.
- We compare the height of the glyph to the height of the cell to see if we need to scale. We prescribe a scale transform if the glyph wouldn't be tall enough to fit the box. (We leave it alone otherwise as some glyphs intentionally overscan the box and scaling them can cause banding effects.)
- We inspect the overhang/underhang above and below the boxes and translate transform them (slide them) so they cover the entire cell area.
- We repeat the previous two steps but in the horizontal direction.
## Validation Steps Performed
- See these commments:
- https://github.com/microsoft/terminal/issues/455#issuecomment-620248375
- https://github.com/microsoft/terminal/issues/455#issuecomment-621533916
- https://github.com/microsoft/terminal/issues/455#issuecomment-622585453
Also see the below one with more screenshots:
- https://github.com/microsoft/terminal/pull/5743#issuecomment-624940567
## Summary of the Pull Request
- Improves the correction of the scaling and spacing that is applied to
glyphs if they are too large or too small for the number of columns that
the text buffer is expecting
## References
- Supersedes #4438
Co-authored-by: Mili (Yi) Zhang <milizhang@gmail.com>
- Related to #4704 (#4731)
## PR Checklist
* [x] Closes#696
* [x] Closes#4375
* [x] Closes#4708
* [x] Closes a crash that @DHowett-MSFT complained about with
`"x" * ($Host.UI.RawUI.BufferSize.Width - 1) + "`u{241b}"`
* [x] Eliminates an exception getting thrown with the U+1F3E0 emoji in
`_CorrectGlyphRun`
* [x] Corrects several graphical issues that occurred after #4731 was
merged to master (weird repeats and splits of runs)
* [x] I work here.
* [x] Tested manually versus given scenarios.
* [x] Documentation written into comments in the code.
* [x] I'm a core contributor.
## Detailed Description of the Pull Request / Additional comments
- The `_CorrectGlyphRun` function now walks through and uses the
`_glyphClusters` map to determine the text span and glyph span for each
cluster so it can be considered as a single unit for scaling.
- The total number of columns expected across the entire cluster
text/glyph unit is considered for the available spacing for drawing
- The total glyph advances are summed to see how much space they will
take
- If more space than necessary to draw, all glyphs in the cluster are
offset into the center and the extra space is padded onto the advance of
the last glyph in the range.
- If less space than necessary to draw, the entire cluster is marked for
shrinking as a single unit by providing the initial text index and
length (that is back-mapped out of the glyph run) up to the parent
function so it can use the `_SetCurrentRun` and `_SplitCurrentRun`
existing functions (which operate on text) to split the run into pieces
and only scale the one glyph cluster, not things next to it as well.
- The scale factor chosen for shrinking is now based on the proportion
of the advances instead of going through some font math wizardry
- The parent that calls the run splitting functions now checks to not
attempt to split off text after the cluster if it's already at the end.
This was @DHowett-MSFT's crash.
- The split run function has been corrected to fix the `glyphStart`
position of the back half (it failed to `+=` instead of `=` which
resulted in duplicated text, sometimes).
- Surrogate pair emoji were not allocating an appropriate number of
`_textClusterColumns`. The constructor has been updated such that the
trailing half of surrogate pairs gets a 0 column width (as the lead is
marked appropriately by the `GetColumns()` function). This was the
exception thrown.
- The `_glyphScaleCorrections` array stored up over the calls to
`_CorrectGlyphRun` now uses a struct `ScaleCorrection` as we're up to 3
values.
- The `ScaleCorrection` values are named to clearly indicate they're in
relation to the original text span, not the glyph spans.
- The values that are used to construct `ScaleCorrection`s within
`_CorrectGlyphRun` have been double checked and corrected to not
accidentally use glyph index/counts when text index/counts are what's
required.
## Validation Steps Performed
- Tested the utf82.txt file from one of the linked bugs. Looked
specifically at Burmese through Thai to ensure restoration (for the most
part) of the behavior
- Ensured that U+1f3e0 emoji (🏠) continues to draw correctly
- Checked Fixedsys Excelsior font to ensure it's not shrinking the line
with its ligatures
- Checked ligatureness of Cascadia Code font
- Checked combining characters U+0300-U+0304 with a capital A
## Summary of the Pull Request
- Height adjustment of a glyph is now restricted to itself in the DX
renderer instead of applying to the entire run
- ConPTY compensates for drawing the right half of a fullwidth
character. The entire render base has this behavior restored now as
well.
## PR Checklist
* [x] Closes#2191
* [x] I work here
* [x] Tests added/passed
* [x] No doc
* [x] Am core contributor.
## Detailed Description of the Pull Request / Additional comments
Two issues:
1. On the DirectX renderer side, when confronted with shrinking a glyph,
the correction code would apply the shrunken size to the entire run, not
just the potentially individual glyph that needed to be reduced in size.
Unfortunately while adjusting the horizontal X width can be done for
each glyph in a run, the vertical Y height has to be adjusted for an
entire run. So the solution here was to split the individual glyph
needing shrinking out of the run into its own run so it can be shrunk.
2. On the ConPTY side, there was a long standing TODO that was never
completed to deal with a request to draw only the right half of a
two-column character. This meant that when encountering a request for
the right half only, we would transmit the entire full character to be
drawn, left and right halves, struck over the right half position. Now
we correct the cursor back a position (if space) and draw it out so the
right half is struck over where we believe the right half should be (and
the left half is updated as well as a consequence, which should be OK.)
The reason this happens right now is because despite VIM only updating
two cells in the buffer, the differential drawing calculation in the
ConPTY is very simplistic and intersects only rectangles. This means
from the top left most character drawn down to the row/col cursor count
indicator in vim's modeline are redrawn with each character typed. This
catches the line below the edited line in the typing and refreshes it.
But incorrectly.
We need to address making ConPTY smarter about what it draws
incrementally as it's clearly way too chatty. But I plan to do that with
some of the structures I will be creating to solve #778.
## Validation Steps Performed
- Ran the scenario listed in #2191 in vim in the Terminal
- Added unit tests similar to examples given around glyph/text mapping
in runs from Microsoft community page
Certain DirectX features are unavailable on windows 7. The important ones as they are used in the DX renderer are color font rendering and fallback font support. Color fonts did not exist at all on windows 7 so running basic glyphrun rendering should work just fine.
Fallback font support was not exposed to the user in windows 7, making dealing with them difficult. Rather than try to get some workarounds to properly enable it I have opted to just conditionally disable the support on windows 7.
This encompasses a handful of problems with column counting.
The Terminal project didn't set a fallback column counter. Oops. I've fixed this to use the `DxEngine` as the fallback.
The `DxEngine` didn't implement its fallback method. Oops. I've fixed this to use the `CustomTextLayout` to figure out the advances based on the same font and fallback pattern as the real final layout, just without "rounding" it into cells yet.
- `CustomTextLayout` has been updated to move the advance-correction into a separate phase from glyph shaping. Previously, we corrected the advances to nice round cell counts during shaping, which is fine for drawing, but hard for column count analysis.
- Now that there are separate phases, an `Analyze` method was added to the `CustomTextLayout` which just performs the text analysis steps and the glyph shaping, but no advance correction to column boundaries nor actual drawing.
I've taken the caching code that I was working on to improve chafa, and I've brought it into this. Now that we're doing a lot of fallback and heavy lifting in terms of analysis via the layout, we should cache the results until the font changes.
I've adjusted how column counting is done overall. It's always been in these phases:
1. We used a quick-lookup of ranges of characters we knew to rapidly decide `Narrow`, `Wide` or `Invalid` (a.k.a. "I dunno")
2. If it was `Invalid`, we consulted a table based off of the Unicode standard that has either `Narrow`, `Wide`, or `Ambiguous` as a result.
3. If it's still `Ambiguous`, we consult a render engine fallback (usually GDI or now DX) to see how many columns it would take.
4. If we still don't know, then it's `Wide` to be safe.
- I've added an additional flow here. The quick-lookup can now return `Ambiguous` off the bat for some glyph characters in the x2000-x3000 range that used to just be simple shapes but have been retroactively recategorized as emoji and are frequently now using full width color glyphs.
- This new state causes the lookup to go immediately to the render engine if it is available instead of consulting the Unicode standard table first because the half/fullwidth table doesn't appear to have been updated for this nuance to reclass these characters as ambiguous, but we'd like to keep that table as a "generated from the spec" sort of table and keep our exceptions in the "quick lookup" function.
I have confirmed the following things "just work" now:
- The windows logo flag from the demo. (⚫⚪💖✅🌌😊)
- The dotted chart on the side of crossterm demo (•)
- The powerline characters that make arrows with the Consolas patched font (██)
- An accented é
- The warning and checkmark symbols appearing same size as the X. (✔⚠🔥)
Related work items: #21167256, #21237515, #21243859, #21274645, #21296827
