REGRESSION(266134@main): 3D border-style have very low contrast with …

…very dark border-color

https://bugs.webkit.org/show_bug.cgi?id=261847
rdar://115812372

Reviewed by Darin Adler.

266134@main made 3D border styles like groove, ridge, inset, and outset honor the border-color instead of hardcoding a gray color.

Unfortunately, when a dark border-color is used, there is very little contrast between the light border and the dark border.

To fix this, we follow Firefox's algorithm of special casing very dark colors by contrasting 2 lightened versions of the border-color.

See Firefox's algorithm for reference:
https://searchfox.org/mozilla-central/rev/077fc34d03b85b09add26b5f99f1a3a3a72c8720/gfx/wr/webrender/res/cs_border_segment.glsl#112-132

* Source/WebCore/display/css/DisplayBoxDecorationPainter.cpp:
(WebCore::Display::BorderPainter::calculateBorderStyleColor):
* Source/WebCore/rendering/BorderPainter.cpp:
(WebCore::BorderPainter::calculateBorderStyleColor):

Canonical link: https://commits.webkit.org/268265@main

Source/WebCore/display/css/DisplayBoxDecorationPainter.cpp

@@ -174,14 +174,24 @@ void BorderPainter::calculateBorderStyleColor(BorderStyle style, BoxSide side, C
 
     Operation operation = (side == BoxSide::Top || side == BoxSide::Left) == (style == BorderStyle::Inset) ? Darken : Lighten;
 
-    // Here we will darken the border decoration color when needed. This will yield a similar behavior as in FF.
+    bool isVeryDarkColor = color.luminance() <= baseDarkColorLuminance;
+    bool isVeryLightColor = color.luminance() > baseLightColorLuminance;
+
+    // Special case very dark colors to give them extra contrast.
+    if (isVeryDarkColor) {
+        color = operation == Darken ? color.lightened() : color.lightened().lightened();
+        return;
+    }
+
+    // Here we will darken the border decoration color when needed.
     if (operation == Darken) {
-        if (color.luminance() > baseDarkColorLuminance)
-            color = color.darkened();
-    } else {
-        if (color.luminance() < baseLightColorLuminance)
-            color = color.lightened();
+        color = color.darkened();
+        return;
     }
+
+    ASSERT(operation == Lighten);
+
+    color = isVeryLightColor ? color : color.lightened();
 }
 
 // This assumes that we draw in order: top, bottom, left, right.

Source/WebCore/rendering/BorderPainter.cpp

@@ -1422,15 +1422,20 @@ Color BorderPainter::calculateBorderStyleColor(const BorderStyle& style, const B
 
     Operation operation = (side == BoxSide::Top || side == BoxSide::Left) == (style == BorderStyle::Inset) ? Darken : Lighten;
 
-    // Here we will darken the border decoration color when needed. This will yield a similar behavior as in FF.
-    if (operation == Darken) {
-        if (color.luminance() > baseDarkColorLuminance)
-            return color.darkened();
-    } else {
-        if (color.luminance() < baseLightColorLuminance)
-            return color.lightened();
-    }
-    return color;
+    bool isVeryDarkColor = color.luminance() <= baseDarkColorLuminance;
+    bool isVeryLightColor = color.luminance() > baseLightColorLuminance;
+
+    // Special case very dark colors to give them extra contrast.
+    if (isVeryDarkColor)
+        return operation == Darken ? color.lightened() : color.lightened().lightened();
+
+    // Here we will darken the border decoration color when needed.
+    if (operation == Darken)
+        return color.darkened();
+
+    ASSERT(operation == Lighten);
+
+    return isVeryLightColor ? color : color.lightened();
 }
 
 const Document& BorderPainter::document() const