big rendering overhaul (cleaning and api abstraction)

apps/demos/scenery/scenes/ingame.c

@@ -222,7 +222,10 @@ static void ingame_tick(State *state) {
     draw_terrain(scn);
 
     draw_skybox("/assets/miramar/miramar_*.tga");
-    draw_fog(0.9f, 1.0f, 0.05f, (Color){ 140, 147, 160, 255 });
+
+    ctx.fog_color = (Color){ 140, 147, 160, 255 };
+    ctx.fog_start = 0.9f;
+    ctx.fog_density = 0.05f;
 }