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windows: Fix ascent/descent calculations (#40103)

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This applies the same fix as #39886 for Windows.

Previously we were using `GetLineMetrics` to determine the ascent and
descent values for each line. It seems like this has the same behavior
as `GetTypographicBounds` on macOS, which is to return the minimum
ascent and descent for the current state of the `TextLayout` object.
This causes the ascent/descent to be unstable when adding or removing an
emoji because a font fallback is triggered when an emoji is present on
the line.

The issue is fixed by switching to `font.GetMetrics` to get the ascent
and descent, which should always return stable values for the main font,
instead of changing when there's a fallback. This also should support
situations where we have multiple explicit fonts on the same line,
although that probably can't be triggered in Zed right now.

Release Notes:

- windows: Fixed a vertical shift in text layout when inserting or
removing an emoji.

Co-authored-by: Bennet Bo Fenner <bennetbo@gmx.de>
This commit is contained in:
Cole Miller
2025-10-13 09:49:07 -04:00
committed by GitHub
co-authored by Bennet Bo Fenner
parent 02bdba80a4
commit f1db1f3a3c
1 changed files with 12 additions and 10 deletions
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crates/gpui/src/platform/windows/direct_write.rs
+12 -10
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@@ -606,19 +606,21 @@ impl DirectWriteState {
};
let mut first_run = true;
let mut ascent = Pixels::default();
let mut descent = Pixels::default();
let mut max_ascent = 0.0_f32;
let mut max_descent = 0.0_f32;
for run in font_runs {
let font_info = &self.fonts[run.font_id.0];
let mut metrics = std::mem::zeroed();
font_info.font_face.GetMetrics(&mut metrics);
let font_scale = font_size.0 / metrics.Base.designUnitsPerEm as f32;
max_ascent = max_ascent.max(metrics.Base.ascent as f32 * font_scale);
max_descent = max_descent.max(-(metrics.Base.descent as f32 * font_scale));
if first_run {
first_run = false;
let mut metrics = vec![DWRITE_LINE_METRICS::default(); 4];
let mut line_count = 0u32;
text_layout.GetLineMetrics(Some(&mut metrics), &mut line_count as _)?;
ascent = px(metrics[0].baseline);
descent = px(metrics[0].height - metrics[0].baseline);
continue;
}
let font_info = &self.fonts[run.font_id.0];
let current_text = &text[utf8_offset..(utf8_offset + run.len)];
utf8_offset += run.len;
let current_text_utf16_length = current_text.encode_utf16().count() as u32;
@@ -660,8 +662,8 @@ impl DirectWriteState {
Ok(LineLayout {
font_size,
width,
ascent,
descent,
ascent: max_ascent.into(),
descent: max_descent.into(),
runs,
len: text.len(),
})