Commit: patch 9.1.2129: MS-Windows: font size calculation slightly wrong, causing line gaps

[Christian Brabandt]

patch 9.1.2129: MS-Windows: font size calculation slightly wrong, causing line gaps

Commit: https://github.com/vim/vim/commit/b46594eefb575dd473aa075efdb585412e742f66
Author: Yasuhiro Matsumoto <matt...@gmail.com>
Date: Wed Feb 4 15:26:22 2026 +0000

patch 9.1.2129: MS-Windows: font size calculation slightly wrong, causing line gaps

Problem: MS-Windows: font size calculation slightly wrong, causing
vertical line gaps (Maxim Kim, after v9.1.2127)
Solution: Update font size calculation when using DirectX
(Yasuhiro Matsumoto).

Use pre-calculated font ascent from font metrics instead of fixed
formula (h * 0.83) to calculate text baseline. This prevents vertical
text shift when font fallback occurs with CJK characters.

closes: #19318

Signed-off-by: Yasuhiro Matsumoto <matt...@gmail.com>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/runtime/doc/version9.txt b/runtime/doc/version9.txt
index 52d086a87..e0ac515ab 100644
--- a/runtime/doc/version9.txt
+++ b/runtime/doc/version9.txt
@@ -52461,4 +52461,10 @@ Problem: heap UAF if autocommands from reloading a file changed outside
of Vim wipe its buffer.
Solution: Validate the bufref after buf_reload (Sean Dewar).

+Patch 9.1.2129
+Problem: MS-Windows: font size calculation slightly wrong, causing
+ vertical line gaps (Maxim Kim, after v9.1.2127)
+Solution: Update font size calculation when using DirectX
+ (Yasuhiro Matsumoto).
+
vim:tw=78:ts=8:noet:ft=help:norl:fdm=manual:nofoldenable
diff --git a/src/gui_dwrite.cpp b/src/gui_dwrite.cpp
index 5d4cb6c3a..39a39938b 100644
--- a/src/gui_dwrite.cpp
+++ b/src/gui_dwrite.cpp
@@ -206,7 +206,8 @@ public:
IDWriteTextFormat* pTextFormat;
DWRITE_FONT_WEIGHT fontWeight;
DWRITE_FONT_STYLE fontStyle;
- Item() : hFont(NULL), pTextFormat(NULL) {}
+ FLOAT fontAscent;
+ Item() : hFont(NULL), pTextFormat(NULL), fontAscent(0.0f) {}
};

private:
@@ -323,7 +324,7 @@ struct DWriteContext {
void DiscardDeviceResources();

HRESULT CreateTextFormatFromLOGFONT(const LOGFONTW &logFont,
- IDWriteTextFormat **ppTextFormat);
+ IDWriteTextFormat **ppTextFormat, FLOAT *pFontAscent);

HRESULT SetFontByLOGFONT(const LOGFONTW &logFont);

@@ -759,7 +760,7 @@ DWriteContext::DiscardDeviceResources()

HRESULT
DWriteContext::CreateTextFormatFromLOGFONT(const LOGFONTW &logFont,
- IDWriteTextFormat **ppTextFormat)
+ IDWriteTextFormat **ppTextFormat, FLOAT *pFontAscent)
{
// Most of this function is copied from: https://github.com/Microsoft/Windows-classic-samples/blob/master/Samples/Win7Samples/multimedia/DirectWrite/RenderTest/TextHelpers.cpp
HRESULT hr = S_OK;
@@ -769,6 +770,7 @@ DWriteContext::CreateTextFormatFromLOGFONT(const LOGFONTW &logFont,
IDWriteFontFamily *fontFamily = NULL;
IDWriteLocalizedStrings *localizedFamilyNames = NULL;
float fontSize = 0;
+ DWRITE_FONT_METRICS fontMetrics = {};

if (SUCCEEDED(hr))
{
@@ -804,7 +806,6 @@ DWriteContext::CreateTextFormatFromLOGFONT(const LOGFONTW &logFont,
// Use lfHeight of the LOGFONT as font size.
fontSize = float(logFont.lfHeight);

- DWRITE_FONT_METRICS fontMetrics;
font->GetMetrics(&fontMetrics);

// Convert lfHeight to DirectWrite font size
@@ -818,7 +819,7 @@ DWriteContext::CreateTextFormatFromLOGFONT(const LOGFONTW &logFont,
// Positive lfHeight represents the font's cell height (ascent + descent)
// Convert to em height
fontSize = fontSize * float(fontMetrics.designUnitsPerEm)
- / float(fontMetrics.ascent + fontMetrics.descent);
+ / float(fontMetrics.ascent + fontMetrics.descent + fontMetrics.lineGap);
}
}

@@ -861,7 +862,12 @@ DWriteContext::CreateTextFormatFromLOGFONT(const LOGFONTW &logFont,
SafeRelease(&font);

if (SUCCEEDED(hr))
+ {
*ppTextFormat = pTextFormat;
+ if (pFontAscent != NULL && fontMetrics.designUnitsPerEm != 0)
+ *pFontAscent = fontSize * float(fontMetrics.ascent)
+ / float(fontMetrics.designUnitsPerEm);
+ }
else
SafeRelease(&pTextFormat);

@@ -873,8 +879,9 @@ DWriteContext::SetFontByLOGFONT(const LOGFONTW &logFont)
{
HRESULT hr = S_OK;
IDWriteTextFormat *pTextFormat = NULL;
+ FLOAT fontAscent = 0.0f;

- hr = CreateTextFormatFromLOGFONT(logFont, &pTextFormat);
+ hr = CreateTextFormatFromLOGFONT(logFont, &pTextFormat, &fontAscent);

if (SUCCEEDED(hr))
{
@@ -883,6 +890,7 @@ DWriteContext::SetFontByLOGFONT(const LOGFONTW &logFont)
mFontWeight = static_cast<DWRITE_FONT_WEIGHT>(logFont.lfWeight);
mFontStyle = logFont.lfItalic ? DWRITE_FONT_STYLE_ITALIC
: DWRITE_FONT_STYLE_NORMAL;
+ mFontAscent = fontAscent;
}

return hr;
@@ -901,6 +909,7 @@ DWriteContext::SetFont(HFONT hFont)
mTextFormat = item.pTextFormat;
mFontWeight = item.fontWeight;
mFontStyle = item.fontStyle;
+ mFontAscent = item.fontAscent;
mFallbackDC = false;
}
else
@@ -919,6 +928,7 @@ DWriteContext::SetFont(HFONT hFont)
item.pTextFormat = mTextFormat;
item.fontWeight = mFontWeight;
item.fontStyle = mFontStyle;
+ item.fontAscent = mFontAscent;
mFallbackDC = false;
}
else
@@ -1070,13 +1080,13 @@ DWriteContext::DrawText(const WCHAR *text, int len,
textLayout->SetFontWeight(mFontWeight, textRange);
textLayout->SetFontStyle(mFontStyle, textRange);

- // Calculate baseline using a fixed formula based on cell geometry.
+ // Calculate baseline using font ascent from font metrics.
// Do NOT use GetLineMetrics() because it returns different values
// depending on text content (e.g., when CJK characters trigger
// font fallback, the metrics change).
- // Use the same baseline calculation for all text to prevent
+ // Use the pre-calculated font ascent for all text to prevent
// vertical shifts during redraw.
- FLOAT baselineY = floorf(FLOAT(y) + FLOAT(h) * 0.83f + 0.5f);
+ FLOAT baselineY = FLOAT(y) + mFontAscent;

TextRenderer renderer(this);
TextRendererContext context = { color, FLOAT(cellWidth), lpDx, len,
diff --git a/src/version.c b/src/version.c
index c4b596038..1315fb2cb 100644
--- a/src/version.c
+++ b/src/version.c
@@ -734,6 +734,8 @@ static char *(features[]) =

static int included_patches[] =
{ /* Add new patch number below this line */
+/**/
+ 2129,
/**/
2128,
/**/