Add module projection, store projection in Session

and restore the projection of the last session.

src/main.rs

 pub mod ortho_tile_layer;
 pub mod orthografic_view;
 pub mod program;
+pub mod projection;
 pub mod search;
 pub mod session;
 pub mod texture;
 pub mod vertex_attrib;
 
 use coord::{LatLonDeg, ScreenCoord};
-use glutin::{ControlFlow, ElementState, Event, GlContext, MouseButton, MouseScrollDelta, VirtualKeyCode, WindowEvent};
 use glutin::dpi::{LogicalPosition, LogicalSize, PhysicalPosition};
+use glutin::{ControlFlow, ElementState, Event, GlContext, MouseButton, MouseScrollDelta, VirtualKeyCode, WindowEvent};
 use map_view_gl::MapViewGl;
 use std::error::Error;
 use std::sync::mpsc;

src/map_view_gl.rs

 use context::Context;
 use coord::{MapCoord, ScreenCoord};
-use ortho_tile_layer::OrthoTileLayer;
 use map_view::MapView;
 use marker_layer::MarkerLayer;
+use mercator_tile_layer::MercatorTileLayer;
 use mercator_view::MercatorView;
+use ortho_tile_layer::OrthoTileLayer;
+use projection::Projection;
 use session::Session;
 use texture::{Texture, TextureFormat};
 use tile_atlas::TileAtlas;
 use tile_cache::TileCache;
-use mercator_tile_layer::MercatorTileLayer;
 use tile_source::TileSource;
 
 
     last_draw_type: DrawType,
 }
 
-#[derive(Debug, Eq, PartialEq)]
-enum Projection {
-    // EPSG:3857: WGS 84 / Pseudo-Mercator
-    Mercator,
-    // Orthographic projection, WGS 84 coordinates mapped to the sphere
-    Orthografic,
-}
-
 #[derive(Debug, Eq, PartialEq)]
 enum DrawType {
     Null,
         self.map_view.center = session.view_center;
         self.map_view.center.normalize_xy();
         self.map_view.zoom = MIN_ZOOM_LEVEL.max(MAX_ZOOM_LEVEL.min(session.zoom));
+        self.projection = session.projection;
     }
 
     pub fn to_session(&self) -> Session {
             view_center: self.map_view.center,
             zoom: self.map_view.zoom,
             tile_source: None,
+            projection: self.projection,
         }
     }
 }

src/projection.rs

+
+#[derive(Clone, Copy, Debug, Eq, PartialEq)]
+pub enum Projection {
+    // EPSG:3857: WGS 84 / Pseudo-Mercator
+    Mercator,
+    // Orthographic projection, WGS 84 coordinates mapped to the sphere
+    Orthografic,
+}
+
+
+impl Projection {
+    pub fn to_str(&self) -> &str {
+        match *self {
+            Projection::Mercator => "mercator",
+            Projection::Orthografic => "orthografic",
+        }
+    }
+
+    pub fn from_str(s: &str) -> Option<Projection> {
+        match s {
+            "mercator" => Some(Projection::Mercator),
+            "orthografic" => Some(Projection::Orthografic),
+            _ => None,
+        }
+    }
+}

src/session.rs

 use coord::MapCoord;
+use projection::Projection;
 use std::fs::File;
 use std::io::Read;
 use std::path::Path;
-use toml;
 use toml::Value;
 use toml::value::Table;
+use toml;
 
 
 #[derive(Debug)]
     pub view_center: MapCoord,
     pub zoom: f64,
     pub tile_source: Option<String>,
+    pub projection: Projection,
 }
 
 impl Session {
                     None => None,
                 };
 
+                let projection = match view.get("projection") {
+                    Some(&Value::String(ref s)) => {
+                        Projection::from_str(s).unwrap_or_else(|| Projection::Mercator)
+                    },
+                    Some(_) => return Err("projection has to be a string.".to_string()),
+                    None => Projection::Mercator,
+                };
+
                 Ok(
                     Session {
                         view_center: MapCoord::new(x, y),
                         zoom,
                         tile_source,
+                        projection,
                     }
                 )
             },
         if let Some(ref tile_source) = self.tile_source {
             view.insert("tile_source".to_string(), Value::String(tile_source.clone()));
         }
+        view.insert("projection".to_string(), Value::String(self.projection.to_str().to_string()));
 
         let mut root = Table::new();
         root.insert("view".to_string(), Value::Table(view));