Add Color::invert()

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

dgl/Color.hpp

@@ -94,6 +94,11 @@ struct Color {
     */
     Color plus(float value) const noexcept;
 
+   /**
+      Create a new color based on this one but colors inverted.
+    */
+    Color invert() const noexcept;
+
    /**
       Create a color specified by hue, saturation and lightness.
       Values must in [0..1] range.

dgl/src/Color.cpp

@@ -163,6 +163,15 @@ Color Color::plus(const float value) const noexcept
     return color;
 }
 
+Color Color::invert() const noexcept
+{
+    Color color(*this);
+    color.red = 1.f - color.red;
+    color.green = 1.f - color.green;
+    color.blue = 1.f - color.blue;
+    return color;
+}
+
 Color Color::fromHSL(float hue, float saturation, float lightness, float alpha)
 {
     float m1, m2;