From 7a0c35c334071add846da643dd32f5eb083d75d6 Mon Sep 17 00:00:00 2001
From: Radek Dutkiewicz <radicdotkey@gmail.com>
Date: Sun, 8 Mar 2020 13:14:16 +0000
Subject: [PATCH] Added glyph position compensation after autohinting

This improves glyph spacing by subtracting glyph position deltas from glyph advance generated by forced autohinting
---
 include/SFML/Graphics/Glyph.hpp |  2 ++
 src/SFML/Graphics/Font.cpp      | 15 ++++++++++++---
 2 files changed, 14 insertions(+), 3 deletions(-)

diff --git a/include/SFML/Graphics/Glyph.hpp b/include/SFML/Graphics/Glyph.hpp
index 5c6048aa..0e62aa65 100644
--- a/include/SFML/Graphics/Glyph.hpp
+++ b/include/SFML/Graphics/Glyph.hpp
@@ -52,6 +52,8 @@ public:
     // Member data
     ////////////////////////////////////////////////////////////
     float     advance;     //!< Offset to move horizontally to the next character
+    int       lsb_delta;   //!< Left offset after forced autohint. Internally used by getKerning()
+    int       rsb_delta;   //!< Right offset after forced autohint. Internally used by getKerning()
     FloatRect bounds;      //!< Bounding rectangle of the glyph, in coordinates relative to the baseline
     IntRect   textureRect; //!< Texture coordinates of the glyph inside the font's texture
 };
diff --git a/src/SFML/Graphics/Font.cpp b/src/SFML/Graphics/Font.cpp
index b3d474c1..7ef2067f 100644
--- a/src/SFML/Graphics/Font.cpp
+++ b/src/SFML/Graphics/Font.cpp
@@ -40,6 +40,7 @@
 #include FT_STROKER_H
 #include <cstdlib>
 #include <cstring>
+#include <cmath>
 
 
 namespace
@@ -389,16 +390,21 @@ float Font::getKerning(Uint32 first, Uint32 second, unsigned int characterSize)
         FT_UInt index1 = FT_Get_Char_Index(face, first);
         FT_UInt index2 = FT_Get_Char_Index(face, second);
 
+        // Retrieve position compensation deltas generated by FT_LOAD_FORCE_AUTOHINT flag
+        float firstRsbDelta = getGlyph(first, characterSize, false).rsb_delta;
+        float secondLsbDelta = getGlyph(second, characterSize, false).lsb_delta;
+
         // Get the kerning vector
         FT_Vector kerning;
-        FT_Get_Kerning(face, index1, index2, FT_KERNING_DEFAULT, &kerning);
+        FT_Get_Kerning(face, index1, index2, FT_KERNING_UNFITTED, &kerning);
 
         // X advance is already in pixels for bitmap fonts
         if (!FT_IS_SCALABLE(face))
             return static_cast<float>(kerning.x);
 
-        // Return the X advance
-        return static_cast<float>(kerning.x) / static_cast<float>(1 << 6);
+        // Combine kerning with compensation deltas and return the X advance
+        // Flooring is required as we use FT_KERNING_UNFITTED flag which is not quantized in 64 based grid
+        return std::floor((secondLsbDelta - firstRsbDelta + static_cast<float>(kerning.x) + 32) / static_cast<float>(1 << 6));
     }
     else
     {
@@ -624,6 +630,9 @@ Glyph Font::loadGlyph(Uint32 codePoint, unsigned int characterSize, bool bold, f
     if (bold)
         glyph.advance += static_cast<float>(weight) / static_cast<float>(1 << 6);
 
+    glyph.lsb_delta = face->glyph->lsb_delta;
+    glyph.rsb_delta = face->glyph->rsb_delta;
+
     int width  = bitmap.width;
     int height = bitmap.rows;