add color tutorial

Signed-off-by: youhy <[email protected]>

examples/color_example.cc

@@ -24,10 +24,10 @@ int main(int argc, char **argv)
 //! [Create a color]
   ignition::math::Color a = ignition::math::Color(0.3, 0.4, 0.5);
 //! [Create a color]
-
   // The channel order is R, G, B, A and the default alpha value of a should be 1.0
   std::cout << "The alpha value of a should be 1: " << a.A() << std::endl;
 
+
 //! [Set a new color value]
   a.ignition::math::Color::Set(0.6, 0.7, 0.8, 1.0);
 //! [Set a new color value]
@@ -38,14 +38,20 @@ int main(int argc, char **argv)
   ignition::math::Color::BGRA blue = 0xFF0000FF;
   a.ignition::math::Color::SetFromBGRA(blue);
 //! [Set value from BGRA]
+
+//! [Math operator]
   std::cout << "Check if a is Blue: " << (a == ignition::math::Color::Blue) << std::endl;
+  std::cout << "The RGB value of a should be (0, 0, 1): " << a[0] << ", " 
+                                                          << a[1] << ", " 
+                                                          << a[2] << std::endl;
+//! [Math operator]
 
 //! [Set value from HSV]
   // Initialize with HSV. (240, 1.0, 1.0) is blue in HSV.
   a.ignition::math::Color::SetFromHSV(240.0, 1.0, 1.0);
-//! [Set value from HSV]
   std::cout << "The HSV value of a: " << a.HSV() << std::endl;
   std::cout << "The RGBA value of a should be (0, 0, 1, 1): " << a << std::endl;
+//! [Set value from HSV]
 
 }
 //! [complete]

tutorials.md.in

@@ -13,6 +13,7 @@ Ignition @IGN_DESIGNATION_CAP@ library and how to use the library effectively.
 4. \subpage angle "Angle example"
 5. \subpage triangle "Triangle example"
 6. \subpage rotation "Rotation example"
+7. \subpage color "Color example"
 
 ## License
 

tutorials/color.md

@@ -0,0 +1,58 @@
+\page color Color example
+
+This tutorial explains how to use the `Color` class from Ignition Math library.
+
+## Compile the code
+
+Go to `ign-math/examples` and use `cmake` to compile the code:
+
+```{.sh}
+git clone https://github.com/ignitionrobotics/ign-math/ -b ign-math6
+cd ign-math/examples
+mkdir build
+cd build
+cmake ..
+make
+```
+
+When the code is compiled, run:
+
+```{.sh}
+./color_example
+```
+
+The ouput of the program:
+
+```{.sh}
+The alpha value of a should be 1: 1
+The RGBA value of a: 0.6 0.7 0.8 1
+Check if a is Blue: 1
+The RGB value of a should be (0, 0, 1): 0, 0, 1
+The HSV value of a: 4 1 1
+The RGBA value of a should be (0, 0, 1, 1): 0 0 1 1
+```
+
+## Code
+
+Create a color with the following RGBA value. The the alpha value is set default to 1.0:
+
+\snippet examples/color_example.cc Create a color
+
+Change the value of a color via `Set()`. All values are set default to 1.0 if not specify.
+
+\snippet examples/color_example.cc Set a new color value
+
+The ABGR, ARGB, BGRA, RGBA are 4 datatypes that allow you to set color from a 32-bit int. Take BGRA as an example:
+
+\snippet examples/color_example.cc Set value from BGRA
+
+Color class overloads math operators including `+`, `-`, `*`, `/`, `[]`, and `==`.
+
+\snippet examples/color_example.cc Math operator
+
+You can also set or read a color in HSV.
+
+\snippet examples/color_example.cc Set value from HSV
+
+There are more functions in `Color`. Take a look at the [API](https://ignitionrobotics.org/api/math/6.9/classignition_1_1math_1_1Color.html)
+