Update coordinates.md

Original commit: d0dc3a3210

gui/docs/ensogl/coordinates.md

@@ -32,6 +32,55 @@
   <img width="600" src="https://user-images.githubusercontent.com/1623053/85817783-3e23ae00-b76f-11ea-8972-c90f1eb6ba1e.png"/>
 
 
+## Examples
+
+```rust
+use nalgebra as n;
+
+let object_space      = n::Vector4::new(3.0,5.0,7.0,1.0);
+let object_matrix     = n::Matrix4::identity().append_translation(&n::Vector3::new(10.0,0.0,0.0));
+let inv_object_matrix = object_matrix.try_inverse().unwrap();
+
+let camera_matrix   = n::Matrix4::identity().append_translation(&n::Vector3::new(0.0,0.0,100.0));
+let inv_view_matrix = camera_matrix;
+let view_matrix     = camera_matrix.try_inverse().unwrap();
+
+let aspect = 1.0;
+let fov    = 90.0f32.to_radians();
+let near   = 0.1;
+let far    = 100.0;
+let perspective           = n::Perspective3::new(aspect,fov,near,far);
+let projection_matrix     = *perspective.as_matrix();
+let inv_projection_matrix = perspective.inverse();
+
+// let left   = -100.0;
+// let right  = 100.0;
+// let bottom = -100.0;
+// let top    = 100.0;
+// let near   = 0.0;
+// let far    = 100.0;
+// let orthographic          = n::Orthographic3::new(left,right,bottom,top,near,far);
+// let projection_matrix     = *orthographic.as_matrix();
+// let inv_projection_matrix = orthographic.inverse();
+
+let world_space   = object_matrix * object_space;
+let eye_space     = view_matrix * world_space;
+let clip_space    = projection_matrix * eye_space;
+
+let eye_space2    = inv_projection_matrix * clip_space;
+let world_space2  = inv_view_matrix * eye_space2;
+let object_space2 = inv_object_matrix * world_space2;
+
+println!("---------------------------------");
+println!("object_space: {:?}", object_space);
+println!("world_space: {:?}", world_space);
+println!("eye_space: {:?}", eye_space);
+println!("clip_space: {:?}", clip_space);
+println!("eye_space2: {:?}", eye_space2);
+println!("world_space2: {:?}", world_space2);
+println!("object_space2: {:?}", object_space2);
+```
+
 
 ## Sources
 Images and fragments used here are parts of the following articles: