feat: basic texture support

- add texture support (ambient, diffuse, specular)
- use opacity in fragment shader
- calculate normal matrix on cpu for matricies with big determinants

src/ui/ui.rs

@@ -31,6 +31,7 @@ pub struct State {
     pub logger: logger::WritableLog,
     pub settings: Settings,
     pub fps: f32,
+    pub show_textures: bool
 }
 
 impl Default for State {
@@ -55,6 +56,7 @@ impl Default for State {
             logger: logger::WritableLog::default(),
             settings: Settings::default(),
             fps: 0.0,
+            show_textures: true
         }
     }
 }
@@ -487,6 +489,8 @@ fn draw_viewport(ui: &imgui::Ui, state: &mut State, texture: u32) {
             ui.same_line();
             ui.checkbox("FOV zoom", &mut state.fov_zoom);
             ui.same_line();
+            ui.checkbox("Show Textures", &mut state.show_textures);
+            ui.same_line();
             ui.set_next_item_width(150.0);
             imgui::Drag::new("Camera Speed")
                 .range(1.0, 10000.0)