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

src/apps/aboutsystem/AboutSystem.cpp

@@ -913,9 +913,7 @@ SysInfoView::_DesktopTextColor(int32 workspace) const
 		workspace = current_workspace();
 
 	rgb_color viewColor = screen.DesktopColor(workspace);
-	int viewBrightness = BPrivate::perceptual_brightness(viewColor);
-	textColor.blue = textColor.green = textColor.red = viewBrightness > 127
-		? 0 : 255;
+	textColor.blue = textColor.green = textColor.red = viewColor.IsLight() ? 0 : 255;
 	textColor.alpha = 255;
 
 	return textColor;

src/kits/interface/GraphicsDefs.cpp

@@ -15,6 +15,7 @@
 #include <AppServerLink.h>
 #include <ServerProtocol.h>
 
+#include <math.h>
 
 // patterns
 const pattern B_SOLID_HIGH = {{0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}};
@@ -36,11 +37,15 @@ const uint32 B_TRANSPARENT_MAGIC_RGBA32_BIG = 0x77747700;
 const struct screen_id B_MAIN_SCREEN_ID = {0};
 
 
-// rgb_color
 int32
 rgb_color::Brightness() const
 {
-	return ((int32)red * 41 + (int32)green * 187 + (int32)blue * 28) >> 8;
+	// 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.
+
+	return (uint8)roundf(sqrtf(
+		0.299f * red * red + 0.587f * green * green + 0.114 * blue * blue));
 }
 
 

src/kits/tracker/PoseView.cpp

@@ -9158,16 +9158,13 @@ BPoseView::InvertedBackColor() const
 {
 	rgb_color background = ui_color(B_DOCUMENT_BACKGROUND_COLOR);
 	rgb_color inverted = invert_color(background);
-	int textBrightness = BPrivate::perceptual_brightness(inverted);
-	int viewBrightness = BPrivate::perceptual_brightness(background);
 
-	if (abs(viewBrightness - textBrightness) > 127) {
-		// The colors are different enough, we can use inverted
+	// The colors are different enough, we can use inverted
+	if (rgb_color::Contrast(background, inverted) > 127)
 		return inverted;
-	} else {
-		// use black or white
-		return (viewBrightness > 127 ? kBlack : kWhite);
-	}
+
+	// use black or white
+	return background.IsLight() ? kBlack : kWhite;
 }
 
 

src/kits/tracker/PoseView.h

@@ -1043,24 +1043,11 @@ BPoseView::DeskTextColor() const
 	rgb_color textColor = HighColor();
 	rgb_color viewColor = ViewColor();
 
-	int textBrightness = BPrivate::perceptual_brightness(textColor);
-	int viewBrightness = BPrivate::perceptual_brightness(viewColor);
-	if (abs(viewBrightness - textBrightness) > 127) {
-		// The colors are different enough, we can use them as is
+	// The colors are different enough, we can use them as is
+	if (rgb_color::Contrast(viewColor, textColor) > 127)
 		return textColor;
-	} else {
-		if (viewBrightness > 127) {
-			textColor.red = 0;
-			textColor.green = 0;
-			textColor.blue = 0;
-		} else {
-			textColor.red = 255;
-			textColor.green = 255;
-			textColor.blue = 255;
-		}
 
-		return textColor;
-	}
+	return viewColor.IsLight() ? kBlack : kWhite;
 }
 
 

src/kits/tracker/Utilities.cpp

@@ -91,8 +91,7 @@ float
 ReadOnlyTint(rgb_color base)
 {
 	// darken tint if read-only (or lighten if dark)
-	int viewBrightness = BPrivate::perceptual_brightness(base);
-	return viewBrightness > 127 ? B_DARKEN_1_TINT : 0.85;
+	return base.IsLight() ? B_DARKEN_1_TINT : 0.85;
 }