From 374cdd1549562e4e2e47c5950c6cb9589d567e41 Mon Sep 17 00:00:00 2001
From: Benedikt Schroeder <benedikt.schroeder@outlook.de>
Date: Wed, 14 Oct 2020 07:15:00 +0200
Subject: [PATCH 1/2] Use Skia's font metrics

---
 src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs | 44 ++++++++-------------
 1 file changed, 17 insertions(+), 27 deletions(-)

diff --git a/src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs b/src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs
index 5571bd890d..c649f3d8bf 100644
--- a/src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs
+++ b/src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs
@@ -1,6 +1,5 @@
 using System;
 using System.Runtime.InteropServices;
-using Avalonia.Media;
 using Avalonia.Platform;
 using HarfBuzzSharp;
 using SkiaSharp;
@@ -24,40 +23,31 @@ namespace Avalonia.Skia
 
             Font.SetFunctionsOpenType();
 
-            Font.GetScale(out var xScale, out _);
+            DesignEmHeight = (short)Typeface.UnitsPerEm;
 
-            DesignEmHeight = (short)xScale;
+            var metrics = Typeface.ToFont().Metrics;
 
-            if (!Font.TryGetHorizontalFontExtents(out var fontExtents))
-            {
-                Font.TryGetVerticalFontExtents(out fontExtents);
-            }
+            Ascent = (int)(metrics.Ascent / 12.0 * Typeface.UnitsPerEm);
 
-            Ascent = -fontExtents.Ascender;
+            Descent = (int)(metrics.Descent / 12.0 * Typeface.UnitsPerEm);
 
-            Descent = -fontExtents.Descender;
+            LineGap = (int)(metrics.Leading / 12.0 * Typeface.UnitsPerEm);
 
-            LineGap = fontExtents.LineGap;
+            UnderlinePosition = metrics.UnderlinePosition != null ?
+                (int)(metrics.UnderlinePosition / 12.0 * Typeface.UnitsPerEm) :
+                0;
 
-            if (Font.OpenTypeMetrics.TryGetPosition(OpenTypeMetricsTag.UnderlineOffset, out var underlinePosition))
-            {
-                UnderlinePosition = underlinePosition;
-            }
+            UnderlineThickness = metrics.UnderlineThickness != null ?
+                (int)(metrics.UnderlineThickness / 12.0 * Typeface.UnitsPerEm) :
+                0;
 
-            if (Font.OpenTypeMetrics.TryGetPosition(OpenTypeMetricsTag.UnderlineSize, out var underlineThickness))
-            {
-                UnderlineThickness = underlineThickness;
-            }
+            StrikethroughPosition = metrics.StrikeoutPosition != null ?
+                (int)(metrics.StrikeoutPosition / 12.0 * Typeface.UnitsPerEm) :
+                0;
 
-            if (Font.OpenTypeMetrics.TryGetPosition(OpenTypeMetricsTag.StrikeoutOffset, out var strikethroughPosition))
-            {
-                StrikethroughPosition = strikethroughPosition;
-            }
-
-            if (Font.OpenTypeMetrics.TryGetPosition(OpenTypeMetricsTag.StrikeoutSize, out var strikethroughThickness))
-            {
-                StrikethroughThickness = strikethroughThickness;
-            }
+            StrikethroughThickness = metrics.StrikeoutThickness != null ?
+                (int)(metrics.StrikeoutThickness / 12.0 * Typeface.UnitsPerEm) :
+                0;
 
             IsFixedPitch = Typeface.IsFixedPitch;
         }

From 7cb133a33a41a8073a840fe538bfcceafb676604 Mon Sep 17 00:00:00 2001
From: Benedikt Schroeder <benedikt.schroeder@outlook.de>
Date: Wed, 14 Oct 2020 11:50:42 +0200
Subject: [PATCH 2/2] Introduce defaultFontRenderingEmSize

---
 src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs | 16 +++++++++-------
 1 file changed, 9 insertions(+), 7 deletions(-)

diff --git a/src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs b/src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs
index c649f3d8bf..ceccc481f9 100644
--- a/src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs
+++ b/src/Skia/Avalonia.Skia/GlyphTypefaceImpl.cs
@@ -27,26 +27,28 @@ namespace Avalonia.Skia
 
             var metrics = Typeface.ToFont().Metrics;
 
-            Ascent = (int)(metrics.Ascent / 12.0 * Typeface.UnitsPerEm);
+            const double defaultFontRenderingEmSize = 12.0;
 
-            Descent = (int)(metrics.Descent / 12.0 * Typeface.UnitsPerEm);
+            Ascent = (int)(metrics.Ascent / defaultFontRenderingEmSize * Typeface.UnitsPerEm);
 
-            LineGap = (int)(metrics.Leading / 12.0 * Typeface.UnitsPerEm);
+            Descent = (int)(metrics.Descent / defaultFontRenderingEmSize * Typeface.UnitsPerEm);
+
+            LineGap = (int)(metrics.Leading / defaultFontRenderingEmSize * Typeface.UnitsPerEm);
 
             UnderlinePosition = metrics.UnderlinePosition != null ?
-                (int)(metrics.UnderlinePosition / 12.0 * Typeface.UnitsPerEm) :
+                (int)(metrics.UnderlinePosition / defaultFontRenderingEmSize * Typeface.UnitsPerEm) :
                 0;
 
             UnderlineThickness = metrics.UnderlineThickness != null ?
-                (int)(metrics.UnderlineThickness / 12.0 * Typeface.UnitsPerEm) :
+                (int)(metrics.UnderlineThickness / defaultFontRenderingEmSize * Typeface.UnitsPerEm) :
                 0;
 
             StrikethroughPosition = metrics.StrikeoutPosition != null ?
-                (int)(metrics.StrikeoutPosition / 12.0 * Typeface.UnitsPerEm) :
+                (int)(metrics.StrikeoutPosition / defaultFontRenderingEmSize * Typeface.UnitsPerEm) :
                 0;
 
             StrikethroughThickness = metrics.StrikeoutThickness != null ?
-                (int)(metrics.StrikeoutThickness / 12.0 * Typeface.UnitsPerEm) :
+                (int)(metrics.StrikeoutThickness / defaultFontRenderingEmSize * Typeface.UnitsPerEm) :
                 0;
 
             IsFixedPitch = Typeface.IsFixedPitch;