Add Color::asGrayscale()

Signed-off-by: falkTX <falktx@falktx.com>

dgl/Color.hpp

@@ -99,6 +99,11 @@ struct Color {
     */
     Color invert() const noexcept;
 
+   /**
+      Create a new color based on this one but in grayscale (using weighted average).
+    */
+    Color asGrayscale() const noexcept;
+
    /**
       Create a color specified by hue, saturation and lightness.
       Values must in [0..1] range.

dgl/src/Color.cpp

@@ -172,6 +172,14 @@ Color Color::invert() const noexcept
     return color;
 }
 
+Color Color::asGrayscale() const noexcept
+{
+    Color color(*this);
+    // values taken from https://goodcalculators.com/rgb-to-grayscale-conversion-calculator/
+    color.red = color.green = color.blue = 0.299f * color.red + 0.587f * color.green + 0.114f * color.blue;
+    return color;
+}
+
 Color Color::fromHSL(float hue, float saturation, float lightness, float alpha)
 {
     float m1, m2;