From fd9c9788f73cb088229701dd92443aa04005a4a3 Mon Sep 17 00:00:00 2001
From: Eskil Abrahamsen Blomfeldt <eskil.abrahamsen-blomfeldt@qt.io>
Date: Tue, 26 Nov 2024 10:47:30 +0100
Subject: Don't support subpixel positioning for color fonts

This comes at a price and it does not really make sense for
emojis.

Pick-to: 6.8
Change-Id: I57148bff48a48bb81a03203626df25646c9acb6a
Reviewed-by: Eirik Aavitsland <eirik.aavitsland@qt.io>

diff --git a/src/gui/text/coretext/qfontengine_coretext_p.h b/src/gui/text/coretext/qfontengine_coretext_p.h
index 1b8a7e0d2a..726abd61d5 100644
--- a/src/gui/text/coretext/qfontengine_coretext_p.h
+++ b/src/gui/text/coretext/qfontengine_coretext_p.h
@@ -54,7 +54,7 @@ public:
     bool canRender(const QChar *string, int len) const override;
 
     int synthesized() const override { return synthesisFlags; }
-    bool supportsHorizontalSubPixelPositions() const override { return true; }
+    bool supportsHorizontalSubPixelPositions() const override { return !isColorFont(); }
     bool supportsVerticalSubPixelPositions() const override { return false; }
 
     QFixed lineThickness() const override;
diff --git a/src/gui/text/freetype/qfontengine_ft_p.h b/src/gui/text/freetype/qfontengine_ft_p.h
index d2fa82b81d..924131699a 100644
--- a/src/gui/text/freetype/qfontengine_ft_p.h
+++ b/src/gui/text/freetype/qfontengine_ft_p.h
@@ -158,8 +158,9 @@ private:
     QFixed emSquareSize() const override;
     bool supportsHorizontalSubPixelPositions() const override
     {
-        return default_hint_style == HintLight ||
-               default_hint_style == HintNone;
+        return !isColorFont()
+                && (default_hint_style == HintLight ||
+                    default_hint_style == HintNone);
     }
 
     bool supportsVerticalSubPixelPositions() const override
diff --git a/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp b/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
index 3ab6fe723d..049a3e5885 100644
--- a/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
+++ b/src/gui/text/windows/qwindowsfontenginedirectwrite.cpp
@@ -749,7 +749,8 @@ QImage QWindowsFontEngineDirectWrite::alphaMapForGlyph(glyph_t glyph,
 bool QWindowsFontEngineDirectWrite::supportsHorizontalSubPixelPositions() const
 {
     DWRITE_RENDERING_MODE renderMode = hintingPreferenceToRenderingMode(fontDef);
-    return  (renderMode != DWRITE_RENDERING_MODE_GDI_CLASSIC
+    return  (!isColorFont()
+            && renderMode != DWRITE_RENDERING_MODE_GDI_CLASSIC
             && renderMode != DWRITE_RENDERING_MODE_GDI_NATURAL
             && renderMode != DWRITE_RENDERING_MODE_ALIASED);
 }