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 <mattn.jp@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

diff --git a/src/gui_dwrite.cpp b/src/gui_dwrite.cpp
index 4f24390775ed623f51621051762027eebd1056c0..b228d28f55a71c0c66516805c42894118f6edefe 100644 (file)
--- 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 011a4d1e6d18998f10a21a77ca0489b4d050ea27..e18b2c8c3f9825d36ed53a04fbafb7b9dc732686 100644 (file)
--- 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,
 /**/