core.git: include/tools tools/source

[Heiko Tietze (via logerrit)]

 include/tools/color.hxx        |   19 +++++++------------
 tools/source/generic/color.cxx |   31 +++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+), 12 deletions(-)

New commits:
commit 74d910231c5591f5e497fc52f2a0132c8f41a271
Author:     Heiko Tietze <tietze.he...@gmail.com>
AuthorDate: Wed Aug 14 13:49:50 2024 +0200
Commit:     Heiko Tietze <heiko.tie...@documentfoundation.org>
CommitDate: Fri Aug 16 08:55:54 2024 +0200

    Resolves tdf#161766 - WCAG 2.1 compliant luminance for isDark()
    
    Alternative solution to I63b85694584cdc6213e7b904ed6402b6c2f2b422
    
    Change-Id: Ifca47de30616295a9965b9313886456313921401
    Reviewed-on: https://gerrit.libreoffice.org/c/core/+/171862
    Reviewed-by: Heiko Tietze <heiko.tie...@documentfoundation.org>
    Tested-by: Jenkins

diff --git a/include/tools/color.hxx b/include/tools/color.hxx
index 653111c50bb4..5d2052e297a4 100644
--- a/include/tools/color.hxx
+++ b/include/tools/color.hxx
@@ -282,6 +282,11 @@ public:
         return sal_uInt8((GetBlue() * 29UL + GetGreen() * 151UL + GetRed() * 
76UL) >> 8);
     }
 
+    /** Gets the color luminance following WCAG 2.1.
+      * @return luminance
+      */
+    sal_uInt8 GetWCAGLuminance() const;
+
     /** Increases the color luminance by cLumInc.
       * @param cLumInc
       */
@@ -300,22 +305,12 @@ public:
     /** Comparison with luminance thresholds.
       * @return is dark
       */
-    bool IsDark() const
-    {
-        // tdf#156182, and band aid for follow-up issues
-        if (mValue == 0x729fcf) // COL_DEFAULT_SHAPE_FILLING
-            return GetLuminance() <= 62;
-        else
-            return GetLuminance() <= 156;
-    }
+    bool IsDark() const;
 
     /** Comparison with luminance thresholds.
       * @return is dark
       */
-    bool IsBright() const
-    {
-        return GetLuminance() >= 245;
-    }
+    bool IsBright() const;
 
     /* Color filters */
 
diff --git a/tools/source/generic/color.cxx b/tools/source/generic/color.cxx
index 208a6caee883..0834b0946722 100644
--- a/tools/source/generic/color.cxx
+++ b/tools/source/generic/color.cxx
@@ -31,6 +31,37 @@
 #include <basegfx/color/bcolortools.hxx>
 #include <basegfx/numeric/ftools.hxx>
 
+static inline double NormalizeRGB(double nValue)
+{
+    if (nValue < 0.04045)
+        return nValue/12.92;
+    else
+        return pow((nValue+0.055)/1.055, 2.4);
+}
+
+sal_uInt8 Color::GetWCAGLuminance() const
+{
+    // https://www.w3.org/TR/WCAG21/#dfn-relative-luminance
+    const double nRed = NormalizeRGB(R/255.0);
+    const double nGreen = NormalizeRGB(G/255.0);
+    const double nBlue = NormalizeRGB(B/255.0);
+    return (nRed * 0.2126 + nGreen * 0.7152 + nBlue * 0.0722) * 255UL;
+}
+
+bool Color::IsDark() const
+{
+    if (mValue == 0x729fcf) // COL_DEFAULT_SHAPE_FILLING
+        return GetLuminance() <= 62;
+    else
+        return GetWCAGLuminance() <= 87;
+}
+
+bool Color::IsBright() const
+{
+    return !IsDark();
+//    return GetLuminance() >= 245;
+}
+
 void Color::IncreaseLuminance(sal_uInt8 cLumInc)
 {
     R = sal_uInt8(std::clamp(R + cLumInc, 0, 255));