Skip glyph shaping analysis when the entire text is simple

src/renderer/dx/CustomTextLayout.cpp

@@ -63,6 +63,24 @@ CustomTextLayout::CustomTextLayout(gsl::not_null<IDWriteFactory1*> const factory
 
         _text += text;
     }
+
+    const auto textLength = gsl::narrow<UINT32>(_text.size());
+
+    BOOL isTextSimple = FALSE;
+    UINT32 uiLengthRead = 0;
+    const UINT32 glyphStart = 0;
+
+    _glyphIndices.resize(textLength);
+
+    const HRESULT hr = _analyzer->GetTextComplexity(
+        _text.c_str(),
+        textLength,
+        _font.Get(),
+        &isTextSimple,
+        &uiLengthRead,
+        &_glyphIndices.at(glyphStart));
+
+    _isEntireTextSimple = SUCCEEDED(hr) && isTextSimple && uiLengthRead == textLength;
 }
 
 // Routine Description:
@@ -149,11 +167,7 @@ CustomTextLayout::CustomTextLayout(gsl::not_null<IDWriteFactory1*> const factory
         // Allocate enough room to have one breakpoint per code unit.
         _breakpoints.resize(_text.size());
 
-        BOOL isTextSimple = FALSE;
-        UINT32 uiLengthRead = 0;
-        RETURN_IF_FAILED(_analyzer->GetTextComplexity(_text.c_str(), textLength, _font.Get(), &isTextSimple, &uiLengthRead, NULL));
-
-        if (!(isTextSimple && uiLengthRead == _text.size()))
+        if (!_isEntireTextSimple)
         {
             // Call each of the analyzers in sequence, recording their results.
             RETURN_IF_FAILED(_analyzer->AnalyzeLineBreakpoints(this, 0, textLength, this));
@@ -274,6 +288,39 @@ CustomTextLayout::CustomTextLayout(gsl::not_null<IDWriteFactory1*> const factory
             _glyphIndices.resize(totalGlyphsArrayCount);
         }
 
+        if (_isEntireTextSimple)
+        {
+            // When the entire text is simple, we can skip GetGlyphs and directly retrieve glyph indices and
+            // advances(in font design unit). With the help of font metrics, we can calculate the actual glyph
+            // advances without the need of GetGlyphPlacements. This shortcut will significantly reduce the time
+            // needed for text analysis.
+            DWRITE_FONT_METRICS1 metrics;
+            run.fontFace->GetMetrics(&metrics);
+
+            // With simple text, there's only one run. The actual glyph count is the same as textLength.
+            _glyphDesignUnitAdvances.resize(textLength);
+            _glyphAdvances.resize(textLength);
+            _glyphOffsets.resize(textLength);
+
+            USHORT designUnitsPerEm = metrics.designUnitsPerEm;
+
+            RETURN_IF_FAILED(_font->GetDesignGlyphAdvances(
+                textLength,
+                &_glyphIndices.at(glyphStart),
+                &_glyphDesignUnitAdvances.at(glyphStart),
+                run.isSideways));
+
+            for (size_t i = glyphStart; i < _glyphAdvances.size(); i++)
+            {
+                _glyphAdvances.at(i) = (float)_glyphDesignUnitAdvances.at(i) / designUnitsPerEm * _format->GetFontSize() * run.fontScale;
+            }
+
+            run.glyphCount = textLength;
+            glyphStart += textLength;
+
+            return S_OK;
+        }
+
         std::vector<DWRITE_SHAPING_TEXT_PROPERTIES> textProps(textLength);
         std::vector<DWRITE_SHAPING_GLYPH_PROPERTIES> glyphProps(maxGlyphCount);
 
@@ -369,6 +416,11 @@ CustomTextLayout::CustomTextLayout(gsl::not_null<IDWriteFactory1*> const factory
 // - S_OK or suitable DirectWrite or STL error code
 [[nodiscard]] HRESULT CustomTextLayout::_CorrectGlyphRuns() noexcept
 {
+    if (_isEntireTextSimple)
+    {
+        return S_OK;
+    }
+
     try
     {
         // Correct each run separately. This is needed whenever script, locale,
@@ -508,9 +560,6 @@ try
 
     // We're going to walk through and check for advances that don't match the space that we expect to give out.
 
-    DWRITE_FONT_METRICS1 metrics;
-    run.fontFace->GetMetrics(&metrics);
-
     // Glyph Indices represents the number inside the selected font where the glyph image/paths are found.
     // Text represents the original text we gave in.
     // Glyph Clusters represents the map between Text and Glyph Indices.

src/renderer/dx/CustomTextLayout.h

@@ -180,6 +180,9 @@ namespace Microsoft::Console::Render
 
         // Glyph shaping results
 
+        // Whether the entire text is determined to be simple and does not require full script shaping.
+        bool _isEntireTextSimple;
+
         std::vector<DWRITE_GLYPH_OFFSET> _glyphOffsets;
 
         // Clusters are complicated. They're in respect to each individual run.
@@ -191,6 +194,9 @@ namespace Microsoft::Console::Render
         // This appears to be the index of the glyph inside each font.
         std::vector<UINT16> _glyphIndices;
 
+        // This is for calculating glyph advances when the entire text is simple.
+        std::vector<INT32> _glyphDesignUnitAdvances;
+
         std::vector<float> _glyphAdvances;
 
         struct ScaleCorrection