rgb_color: Add new APIs: Contrast(), IsLight(), IsDark()

- Remove perceptual_brightness
- Change implementation of rgb_color::Brightness() to the previous BPrivate::perceptual_brightness()
- Introduce convenience methods Contrast(rgb_color), IsLight() and IsDark()

Change-Id: Id677d4a32ce43d73bffecf9baf8cffaafb01a16d
Reviewed-on: https://review.haiku-os.org/c/haiku/+/7399
Reviewed-by: waddlesplash <[email protected]>

headers/os/interface/GraphicsDefs.h

@@ -59,6 +59,28 @@ typedef struct rgb_color {
 
 	int32 Brightness() const;
 
+	inline bool
+	IsDark() const
+	{
+		return Brightness() <= 127;
+	}
+
+	inline bool
+	IsLight() const
+	{
+		return Brightness() > 127;
+	}
+
+	static inline int32
+	Contrast(rgb_color colorA, rgb_color colorB)
+	{
+		int32 contrast = colorA.Brightness() - colorB.Brightness();
+		if (contrast < 0)
+			return -contrast;
+
+		return contrast;
+	}
+
 	inline bool
 	operator==(const rgb_color& other) const
 	{

headers/private/interface/ColorConversion.h

@@ -65,19 +65,6 @@ private:
 };
 
 
-static inline uint8 perceptual_brightness(rgb_color color)
-{
-	// From http://alienryderflex.com/hsp.html
-	// Useful in particular to decide if the color is "light" or "dark"
-	// by checking if the perceptual brightness is > 127.
-	int r = color.red;
-	int g = color.green;
-	int b = color.blue;
-
-	return (uint8)roundf(sqrtf(
-		0.299f * r * r + 0.587f * g * g + 0.114 * b * b));
-}
-
 }	// namespace BPrivate
 
 #endif