DevJockeys Game Development Blog

Building blocks

The game has an open world. I want the player to be able to build and demolish. For that I started searching for a way to place and remove blocks, and to save the state of the game. That was a challenge! Let’s start with placing and removing blocks.

The grid

In the basis, building blocks is as simple as placing a sprite at the mouse x and y position. This however results in a mesh. By using a grid the blocks are placed in a proper position. The blocks are 8 by 8 pixels, so the coordinates of the blocks should be in a grid of 8 by 8.

When clicking the mouse on e.g. x=36,y=27, the block should be placed at x=32, y=24 (divisable by 8). I found the following simple solution:

var offsetX = _x%gridSize;
var offsetY = _y%gridSize;

  var _gridSize = 8;
  _x = mouse_x;
  _y = mouse_y;

  var _offsetX = _x%_gridSize;
  var _offsetY = _y%_gridSize;
        
  _x -= offsetX; 
  _y += -offsetY;

This did the trick, by using _x and _y, blocks are placed exactly in the grid. Of course a lot of other code was needed to get it done, but this was the starting point.

Saving

Saving the game state was a hard one. I could not find any ready-made function for that in gamemaker. There are some (using buffers), but they don’t work, are obsolete, or can not handle huge amounts of data (the gamemaker docs suggest you build your own system).

In my game, thousands of blocks can be placed and/or removed. When the player exits the game and starts it again, the blocks should be where they were when the player left.

I accomplished this by using an array. Everytime a block is placed or removed, an entry is added to the array. When the player exits the game, the array is saved to a file. When the player starts the game, the array is loaded, parsed, and the blocks are placed in the game room.

To make this work, I avoided complicated string functions (like string_pos), because they use a lot of resources.

The (mock-up) code:

function SAVE_GAME(){
// Called when exiting the game
   SAVE_TILE_DATA();
}

function LOAD_GAME(){
   STRING_TO_TILES();
}

function STRING_TO_TILES(){
  var commaSeparator = ord("B");

  LOAD_TILE_DATA();
  var tmp = string(global.TILE_DATA);

  tmp = string_replace_all(tmp, "\"", "");
  tmp = string_replace_all(tmp, "[", "");
  tmp = string_replace_all(tmp, "]", "");
  tmp = string_replace_all(tmp, " ", "");

  global.TILE_ARRAY = [];

  var cnt  = string_length(tmp);

  if (string_length(tmp)>3){
      global.TILE_ARRAY = string_split(tmp,",");
  }
}

function ADD_TO_TILE_ARRAY(pX,pY,pTag){
  // called when player adds or removes block. 
  var commaSeparator = "B";
  var tmp=string(pX) + commaSeparator + string(pY) + pTag;
  var cnt = array_length(global.TILE_ARRAY);
  global.TILE_ARRAY[cnt] = tmp;
}

function SAVE_TILE_DATA(){
  global.TILE_ARRAY = array_unique(global.TILE_ARRAY);
  var file;
  file = file_text_open_write("D:\data.txt"); // sandboxing off in project settings
  file_text_write_string(file,    string(global.TILE_ARRAY));
  file_text_close(file);
}

function LOAD_TILE_DATA(){

if (file_exists("D:\data.txt"))
{
    var file = file_text_open_read("D:\data.txt");
    global.TILE_DATA = file_text_read_string(file);
    file_text_close(file);
} 
}

function SETUP_TILES(){
// called when starting the game
LOAD_GAME();
var cnt = array_length(global.TILE_ARRAY);

for(var i = 0; i<cnt;i++){

    var tmp = global.TILE_ARRAY[i];

    // split entry
   if (string_ends_with(tmp,"E")){
        // SET EMPTY TILE
        tmp = string_replace(tmp,"E","");
        var a[];
        a = string_split(tmp,"B");

        var _x = a[0];
        var _y = a[1];
        // place empty
        tilemap_set_at_pixel(tilemap, 0, _x, _y);

    }else{
        //SET TILE
        tmp = string_replace(tmp,"P","");
        var a[];
        a = string_split(tmp,"B");

        var _x = a[0];
        var _y = a[1];
        // place tile
        tilemap_set_at_pixel(tilemap, 1, _x, _y);
    }
}
}

So, when the player places a block, the block is added to the array (ADD_TO_TILE_ARRAY)

When the player exits the game, SAVE_GAME is called.

When the game starts, SETUP_TILES is called.

My first thought was to make a top-down game. When I started trying some things, I found out that a front-view platform style would be more versatile. I did a small graybox: movement, sword attack, gathering, jumping and … a ladder. The player carries a ladder that can be used to climb to higher platforms. By gathering ladder pieces, the ladder gets longer.

Just a graybox video, nothing more: