Blit tiles to map.

src/bit.ml

@@ -1,4 +1,6 @@
 let is_set num i =
-  if i < 0 then failwith "Invalid bit index."
+  if i < 0 then
+    failwith "Invalid bit index."
+  else
     (num lsr i) land 0b00000001 <> 0
 

src/screen.ml

@@ -51,3 +51,41 @@ let init_screen w h =
     height = h;
     data = Array.make_matrix h w { r = 255; g = 255; b = 255; a = 255 }
   }
+
+
+let render_map mem map_addr =
+  let tile_size = 16 in
+  let map = Bytes.create (32 * 32 * tile_size) in
+  for y = 0 to (32 - 1) do
+    for x = 0 to (32 - 1) do
+      let tile_number = Memory.get mem (map_addr + (y * 32 + x)) |> int_of_char in
+      let src_offset = map_addr + tile_number * tile_size in
+      let tile_line_size = 2 in
+      let tile_height = 8 in
+
+      for line_index = 0 to (tile_height - 1) do
+        let line_offset = src_offset + (line_index * tile_line_size) in
+        let dst_y = y * tile_height + line_index in
+        let dst_offset = (dst_y * 32 + x) * tile_line_size in
+        Bytes.blit mem.vram line_offset map dst_offset tile_line_size
+      done
+    done
+  done
+
+
+let render mem =
+  let
+  {
+    lcd_display_enable;
+    tile_map_select;
+    window_display_enable;
+    tile_data_select;
+    bg_tile_map_select;
+    sprite_size;
+    sprite_enable;
+    bg_display;
+  } = get_lcd_control mem in
+  let scy = Memory.get mem 0xFF42 |> int_of_char in
+  let scx = Memory.get mem 0xFF43 |> int_of_char in
+  scx + scy
+