Commit: patch 9.1.2125: MS-Windows: DirectX rendering can be improved

[Christian Brabandt]

patch 9.1.2125: MS-Windows: DirectX rendering can be improved

Commit: https://github.com/vim/vim/commit/b39b065d6fde5f214feebab882b8ebba78945035
Author: Yasuhiro Matsumoto <matt...@gmail.com>
Date: Sat Jan 31 16:23:28 2026 +0000

patch 9.1.2125: MS-Windows: DirectX rendering can be improved

Problem: MS-Windows: DirectX rendering can be improved
Solution: Use lpDx advance, fix vertical text shift and correct
font-size calculations (Yasuhiro Matsumoto).

This changes DirectWrite rendering to:
- Respect lpDx-provided advance widths instead of always adjusting to
cell width.
- Use a fixed baseline derived from cell geometry to prevent vertical
shifts when font fallback occurs (e.g. with CJK characters).
- Correctly convert LOGFONT lfHeight to DirectWrite font size using font
metrics for closer GDI compatibility.

closes: #19254

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

diff --git a/src/gui_dwrite.cpp b/src/gui_dwrite.cpp
index 4f2439077..b228d28f5 100644
--- a/src/gui_dwrite.cpp
+++ b/src/gui_dwrite.cpp
@@ -307,6 +307,8 @@ struct DWriteContext {
IDWriteTextFormat *mTextFormat;
DWRITE_FONT_WEIGHT mFontWeight;
DWRITE_FONT_STYLE mFontStyle;
+ FLOAT mFontSize; // Font size in pixels (em height)
+ FLOAT mFontAscent; // Font ascent in pixels

D2D1_TEXT_ANTIALIAS_MODE mTextAntialiasMode;

@@ -367,7 +369,10 @@ public:
AdjustedGlyphRun(
const DWRITE_GLYPH_RUN *glyphRun,
FLOAT cellWidth,
- FLOAT &accum) :
+ FLOAT &accum,
+ const INT *lpDx,
+ int *glyphIndex,
+ int cchText) :
DWRITE_GLYPH_RUN(*glyphRun),
mAccum(accum),
mDelta(0.0f),
@@ -377,7 +382,18 @@ public:
for (UINT32 i = 0; i < glyphRun->glyphCount; ++i)
{
FLOAT orig = glyphRun->glyphAdvances[i];
- FLOAT adjusted = adjustToCell(orig, cellWidth);
+ FLOAT adjusted;
+
+ if (*glyphIndex < cchText)
+ {
+ adjusted = FLOAT(lpDx[*glyphIndex]);
+ (*glyphIndex)++;
+ }
+ else
+ {
+ adjusted = adjustToCell(orig, cellWidth);
+ }
+
mAdjustedAdvances[i] = adjusted;
mDelta += adjusted - orig;
}
@@ -403,9 +419,13 @@ struct TextRendererContext {
// const fields.
COLORREF color;
FLOAT cellWidth;
+ const INT *lpDx;
+ int cchText;
+ FLOAT baselineY; // Fixed baseline Y coordinate

// working fields.
FLOAT offsetX;
+ int glyphIndex;
};

class TextRenderer FINAL : public IDWriteTextRenderer
@@ -496,8 +516,14 @@ public:
TextRendererContext *context =
reinterpret_cast<TextRendererContext*>(clientDrawingContext);

+ // Use fixed baseline Y from context instead of DirectWrite's
+ // baselineOriginY to prevent vertical shifts when font fallback
+ // occurs (e.g., for CJK characters).
+ FLOAT fixedBaselineY = context->baselineY;
+
AdjustedGlyphRun adjustedGlyphRun(glyphRun, context->cellWidth,
- context->offsetX);
+ context->offsetX, context->lpDx, &context->glyphIndex,
+ context->cchText);

#ifdef FEAT_DIRECTX_COLOR_EMOJI
if (pDWC_->mDWriteFactory2 != NULL)
@@ -526,7 +552,7 @@ public:
pDWC_->mRT->DrawGlyphRun(
D2D1::Point2F(
colorGlyphRun->baselineOriginX,
- colorGlyphRun->baselineOriginY),
+ fixedBaselineY),
&colorGlyphRun->glyphRun,
pDWC_->mBrush,
DWRITE_MEASURING_MODE_NATURAL);
@@ -542,7 +568,7 @@ public:
pDWC_->mRT->DrawGlyphRun(
D2D1::Point2F(
baselineOriginX + context->offsetX,
- baselineOriginY),
+ fixedBaselineY),
&adjustedGlyphRun,
pDWC_->SolidBrush(context->color),
DWRITE_MEASURING_MODE_NATURAL);
@@ -619,6 +645,8 @@ DWriteContext::DWriteContext() :
mTextFormat(NULL),
mFontWeight(DWRITE_FONT_WEIGHT_NORMAL),
mFontStyle(DWRITE_FONT_STYLE_NORMAL),
+ mFontSize(0.0f),
+ mFontAscent(0.0f),
mTextAntialiasMode(D2D1_TEXT_ANTIALIAS_MODE_DEFAULT)
{
HRESULT hr;
@@ -776,28 +804,25 @@ 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
if (fontSize < 0)
{
- // Negative lfHeight represents the size of the em unit.
+ // Negative lfHeight represents the font's em height in pixels
fontSize = -fontSize;
}
- else
+ else if (fontSize > 0)
{
- // Positive lfHeight represents the cell height (ascent +
- // descent).
- DWRITE_FONT_METRICS fontMetrics;
- font->GetMetrics(&fontMetrics);
-
- // Convert the cell height (ascent + descent) from design units
- // to ems.
- float cellHeight = static_cast<float>(
- fontMetrics.ascent + fontMetrics.descent)
- / fontMetrics.designUnitsPerEm;
-
- // Divide the font size by the cell height to get the font em
- // size.
- fontSize /= cellHeight;
+ // Positive lfHeight represents the font's cell height (ascent + descent)
+ // Convert to em height
+ fontSize = fontSize * float(fontMetrics.designUnitsPerEm)
+ / float(fontMetrics.ascent + fontMetrics.descent);
}
+
+ // Scale by ascent ratio to match GDI rendering size
+ fontSize = ceil(fontSize * float(fontMetrics.ascent) / float(fontMetrics.designUnitsPerEm));
}

// The text format includes a locale name. Ideally, this would be the
@@ -1039,8 +1064,18 @@ 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.
+ // 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
+ // vertical shifts during redraw.
+ FLOAT baselineY = floorf(FLOAT(y) + FLOAT(h) * 0.83f + 0.5f);
+
TextRenderer renderer(this);
- TextRendererContext context = { color, FLOAT(cellWidth), 0.0f };
+ TextRendererContext context = { color, FLOAT(cellWidth), lpDx, len,
+ baselineY, 0.0f, 0 };
+
textLayout->Draw(&context, &renderer, FLOAT(x), FLOAT(y));
}

diff --git a/src/version.c b/src/version.c
index 011a4d1e6..e18b2c8c3 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 */
+/**/
+ 2125,
/**/
2124,
/**/