Add ANSI color contrast adjustment for log view

Automatically adjust log text colors when contrast against background is below WCAG AA standard (4.5:1). Light mode darkens colors, dark mode lightens them. Supports iOS, macOS, and tvOS.
2026-01-08 22:12:45 +08:00
parent 1707a3412a
commit b0f1eed827
3 changed files with 193 additions and 12 deletions
@@ -23,3 +23,151 @@ public extension Color {
        #endif
    }
 }
+
+#if canImport(UIKit)
+    public extension UIColor {
+        var relativeLuminance: CGFloat {
+            var red: CGFloat = 0, green: CGFloat = 0, blue: CGFloat = 0, alpha: CGFloat = 0
+            getRed(&red, green: &green, blue: &blue, alpha: &alpha)
+
+            func linearize(_ c: CGFloat) -> CGFloat {
+                c <= 0.04045 ? c / 12.92 : pow((c + 0.055) / 1.055, 2.4)
+            }
+
+            return 0.2126 * linearize(red) + 0.7152 * linearize(green) + 0.0722 * linearize(blue)
+        }
+
+        static func contrastRatio(_ color1: UIColor, _ color2: UIColor) -> CGFloat {
+            let l1 = color1.relativeLuminance
+            let l2 = color2.relativeLuminance
+            let lighter = max(l1, l2)
+            let darker = min(l1, l2)
+            return (lighter + 0.05) / (darker + 0.05)
+        }
+
+        func adjustedForContrast(against background: UIColor, minRatio: CGFloat = 4.5) -> UIColor {
+            let currentRatio = Self.contrastRatio(self, background)
+            if currentRatio >= minRatio {
+                return self
+            }
+
+            var red: CGFloat = 0, green: CGFloat = 0, blue: CGFloat = 0, alpha: CGFloat = 0
+            getRed(&red, green: &green, blue: &blue, alpha: &alpha)
+
+            let bgLuminance = background.relativeLuminance
+            let shouldDarken = bgLuminance > 0.5
+
+            var low: CGFloat = 0
+            var high: CGFloat = 1
+            var bestColor = self
+
+            for _ in 0 ..< 10 {
+                let mid = (low + high) / 2
+                let adjusted: UIColor
+
+                if shouldDarken {
+                    adjusted = UIColor(
+                        red: red * (1 - mid),
+                        green: green * (1 - mid),
+                        blue: blue * (1 - mid),
+                        alpha: alpha
+                    )
+                } else {
+                    adjusted = UIColor(
+                        red: red + (1 - red) * mid,
+                        green: green + (1 - green) * mid,
+                        blue: blue + (1 - blue) * mid,
+                        alpha: alpha
+                    )
+                }
+
+                let ratio = Self.contrastRatio(adjusted, background)
+                if ratio >= minRatio {
+                    bestColor = adjusted
+                    high = mid
+                } else {
+                    low = mid
+                }
+            }
+
+            return bestColor
+        }
+    }
+#elseif canImport(AppKit)
+    public extension NSColor {
+        var relativeLuminance: CGFloat {
+            guard let rgbColor = usingColorSpace(.sRGB) else {
+                return 0.5
+            }
+
+            var red: CGFloat = 0, green: CGFloat = 0, blue: CGFloat = 0, alpha: CGFloat = 0
+            rgbColor.getRed(&red, green: &green, blue: &blue, alpha: &alpha)
+
+            func linearize(_ c: CGFloat) -> CGFloat {
+                c <= 0.04045 ? c / 12.92 : pow((c + 0.055) / 1.055, 2.4)
+            }
+
+            return 0.2126 * linearize(red) + 0.7152 * linearize(green) + 0.0722 * linearize(blue)
+        }
+
+        static func contrastRatio(_ color1: NSColor, _ color2: NSColor) -> CGFloat {
+            let l1 = color1.relativeLuminance
+            let l2 = color2.relativeLuminance
+            let lighter = max(l1, l2)
+            let darker = min(l1, l2)
+            return (lighter + 0.05) / (darker + 0.05)
+        }
+
+        func adjustedForContrast(against background: NSColor, minRatio: CGFloat = 4.5) -> NSColor {
+            let currentRatio = Self.contrastRatio(self, background)
+            if currentRatio >= minRatio {
+                return self
+            }
+
+            guard let rgbSelf = usingColorSpace(.sRGB) else {
+                return self
+            }
+
+            var red: CGFloat = 0, green: CGFloat = 0, blue: CGFloat = 0, alpha: CGFloat = 0
+            rgbSelf.getRed(&red, green: &green, blue: &blue, alpha: &alpha)
+
+            let bgLuminance = background.relativeLuminance
+            let shouldDarken = bgLuminance > 0.5
+
+            var low: CGFloat = 0
+            var high: CGFloat = 1
+            var bestColor = self
+
+            for _ in 0 ..< 10 {
+                let mid = (low + high) / 2
+                let adjusted: NSColor
+
+                if shouldDarken {
+                    adjusted = NSColor(
+                        red: red * (1 - mid),
+                        green: green * (1 - mid),
+                        blue: blue * (1 - mid),
+                        alpha: alpha
+                    )
+                } else {
+                    adjusted = NSColor(
+                        red: red + (1 - red) * mid,
+                        green: green + (1 - green) * mid,
+                        blue: blue + (1 - blue) * mid,
+                        alpha: alpha
+                    )
+                }
+
+                let ratio = Self.contrastRatio(adjusted, background)
+                if ratio >= minRatio {
+                    bestColor = adjusted
+                    high = mid
+                } else {
+                    low = mid
+                }
+            }
+
+            return bestColor
+        }
+    }
+#endif