Force selection FG to black or white depending on BG luminance (#17753)

Author: DHowett

src/renderer/atlas/AtlasEngine.api.cpp

@@ -432,8 +432,8 @@ void AtlasEngine::SetSelectionBackground(const COLORREF color) noexcept
     {
         auto misc = _api.s.write()->misc.write();
         misc->selectionColor = selectionColor;
-        // Selection Foreground is based on the default foreground; it is also updated in UpdateDrawingBrushes
-        misc->selectionForeground = 0xff000000 | ColorFix::GetPerceivableColor(misc->foregroundColor, color, 0.5f * 0.5f);
+        // Select a black or white foreground based on the perceptual lightness of the background.
+        misc->selectionForeground = ColorFix::GetLuminosity(selectionColor) < 0.5f ? 0xffffffff : 0xff000000;
     }
 }
 

src/renderer/atlas/AtlasEngine.cpp

@@ -658,10 +658,7 @@ try
 
         if (textAttributes.GetForeground().IsDefault() && fg != _api.s->misc->foregroundColor)
         {
-            auto misc = _api.s.write()->misc.write();
-            misc->foregroundColor = fg;
-            // Selection Foreground is based on the default foreground; it is also updated in SetSelectionColor
-            misc->selectionForeground = 0xff000000 | ColorFix::GetPerceivableColor(fg, misc->selectionColor, 0.5f * 0.5f);
+            _api.s.write()->misc.write()->foregroundColor = fg;
         }
     }
 

src/types/ColorFix.cpp

@@ -209,4 +209,9 @@ COLORREF ColorFix::GetPerceivableColor(COLORREF color, COLORREF reference, float
     return linearToColorref(oklab::oklab_to_linear_srgb(colorOklab)) | (color & 0xff000000);
 }
 
+float ColorFix::GetLuminosity(COLORREF color) noexcept
+{
+    return oklab::linear_srgb_to_oklab(colorrefToLinear(color)).l;
+}
+
 TIL_FAST_MATH_END

src/types/inc/ColorFix.hpp

@@ -10,4 +10,5 @@
 namespace ColorFix
 {
     COLORREF GetPerceivableColor(COLORREF color, COLORREF reference, float minSquaredDistance) noexcept;
+    float GetLuminosity(COLORREF color) noexcept;
 }