Added operator - for sf::Color (#114)

include/SFML/Graphics/Color.hpp

@@ -126,6 +126,21 @@ SFML_GRAPHICS_API bool operator !=(const Color& left, const Color& right);
 ////////////////////////////////////////////////////////////
 SFML_GRAPHICS_API Color operator +(const Color& left, const Color& right);
 
+////////////////////////////////////////////////////////////
+/// \relates Color
+/// \brief Overload of the binary - operator
+///
+/// This operator returns the component-wise subtraction of two colors.
+/// Components below 0 are clamped to 0.
+///
+/// \param left  Left operand
+/// \param right Right operand
+///
+/// \return Result of \a left - \a right
+///
+////////////////////////////////////////////////////////////
+SFML_GRAPHICS_API Color operator -(const Color& left, const Color& right);
+
 ////////////////////////////////////////////////////////////
 /// \relates Color
 /// \brief Overload of the binary * operator
@@ -159,6 +174,22 @@ SFML_GRAPHICS_API Color operator *(const Color& left, const Color& right);
 ////////////////////////////////////////////////////////////
 SFML_GRAPHICS_API Color& operator +=(Color& left, const Color& right);
 
+////////////////////////////////////////////////////////////
+/// \relates Color
+/// \brief Overload of the binary -= operator
+///
+/// This operator computes the component-wise subtraction of two colors,
+/// and assigns the result to the left operand.
+/// Components below 0 are clamped to 0.
+///
+/// \param left  Left operand
+/// \param right Right operand
+///
+/// \return Reference to \a left
+///
+////////////////////////////////////////////////////////////
+SFML_GRAPHICS_API Color& operator -=(Color& left, const Color& right);
+
 ////////////////////////////////////////////////////////////
 /// \relates Color
 /// \brief Overload of the binary *= operator

src/SFML/Graphics/Color.cpp

@@ -87,20 +87,30 @@ bool operator !=(const Color& left, const Color& right)
 ////////////////////////////////////////////////////////////
 Color operator +(const Color& left, const Color& right)
 {
-    return Color(static_cast<Uint8>(std::min(left.r + right.r, 255)),
+    return Color(Uint8(std::min(int(left.r) + right.r, 255)),
-                 static_cast<Uint8>(std::min(left.g + right.g, 255)),
+                 Uint8(std::min(int(left.g) + right.g, 255)),
-                 static_cast<Uint8>(std::min(left.b + right.b, 255)),
+                 Uint8(std::min(int(left.b) + right.b, 255)),
-                 static_cast<Uint8>(std::min(left.a + right.a, 255)));
+                 Uint8(std::min(int(left.a) + right.a, 255)));
+}
+
+
+////////////////////////////////////////////////////////////
+Color operator -(const Color& left, const Color& right)
+{
+    return Color(Uint8(std::max(int(left.r) - right.r, 0)),
+                 Uint8(std::max(int(left.g) - right.g, 0)),
+                 Uint8(std::max(int(left.b) - right.b, 0)),
+                 Uint8(std::max(int(left.a) - right.a, 0)));
 }
 
 
 ////////////////////////////////////////////////////////////
 Color operator *(const Color& left, const Color& right)
 {
-    return Color(static_cast<Uint8>(left.r * right.r / 255),
+    return Color(Uint8(int(left.r) * right.r / 255),
-                 static_cast<Uint8>(left.g * right.g / 255),
+                 Uint8(int(left.g) * right.g / 255),
-                 static_cast<Uint8>(left.b * right.b / 255),
+                 Uint8(int(left.b) * right.b / 255),
-                 static_cast<Uint8>(left.a * right.a / 255));
+                 Uint8(int(left.a) * right.a / 255));
 }
 
 
@@ -111,6 +121,13 @@ Color& operator +=(Color& left, const Color& right)
 }
 
 
+////////////////////////////////////////////////////////////
+Color& operator -=(Color& left, const Color& right)
+{
+    return left = left - right;
+}
+
+
 ////////////////////////////////////////////////////////////
 Color& operator *=(Color& left, const Color& right)
 {