HTML5 Canvas [54]
So far, we have only used tiles to simulate sprite-based animated movement. In the next section, we will examine how to use an image tile sheet to create a much more elaborate background using a series of tiles.
Creating a Grid of Tiles
Many games use what is called a tile-based environment for backgrounds and level graphics. We are now going to apply the knowledge we have learned from animating an image on the canvas to create the background maze for our hypothetical game: No Tanks! We will use the same tile sheet from the previous tank examples, but instead of showing the tank sprite tiles, we will create a maze for the tank to move through. We will not actually cover the game-play portion of the code in this chapter because we want to focus on using images to render the screen. In Chapter 9 we will create a simple game using the type of examples shown here.
Defining a Tile Map
We will use the term tile map to refer to a game level or background built from a tile sheet. Take a look back at Figure 4-7—the four row by eight column tile sheet from earlier in this chapter. If we were to create a maze-chase game similar to Pac-Man, we could define the maze using tiles from a tile sheet. The sequence of tiles for our game maze would be considered a tile map.
The first tile is a gray square, which we can use for the “road” tiles between the wall tiles. Any tile that a game sprite can move on is referred to as walkable. Even though our tanks are not literally walking but driving, the concept is the same. In Chapter 9 we will create a small game using these concepts, but for now, let’s concentrate on defining a tile map and displaying it on the canvas.
Our tile map will be a two-dimensional array of tile id numbers. If you recall, the tile id numbers for our tile sheet are in a single dimension, numbering from 0 to 31. Let’s say we are going to create a very small game screen consisting of 10 tiles in length and 10 tiles in height. This means we need to define a tile map of 100 individual tiles (10×10). If our tiles are 32 pixels by 32 pixels, we will define a 320×320 game screen.
There are many ways to define a tile map. One simple way is to use a tile map editor program to lay out a grid of tiles, and then export the data to re-create the tile map in JavaScript. This is precisely how we are going to create our tile map.
Creating a Tile Map with Tiled
The program we are going to use, Tiled, is a great tile map editor that is available for Mac OS, Windows, and Linux. Of course, tile maps can be designed by hand, but map creation is much easier if we utilize a program such as Tiled to do some of the legwork for us. Tiled is available for free under the GNU free software license from http://www.mapeditor.org/.
NOTE
As stated before, you do not need to use this software. Tile maps can be created with other good (and free) software such as Mappy (http://tilemap.co.uk/mappy.php) and Tile Studio (http://tilestudio.sourceforge.net/), and even by hand using MS Paint.
The goal of creating a tile map is to visually lay out a grid of tiles that represents the game screen, and then export the tile ids that represent those tiles. We will use the exported data as a two-dimensional array in our code to build the tile map on the canvas.
Here are the basic steps for creating a simple tile map in Tiled for use in the following section:
Create a new tile map from the File menu. When it asks for Orientation, select Orthogonal with a Map Size of 10×10 and a Tile Size of 32×32.
From the Map menu, import the tanks_sheet.png to be used as the tile set. Select “New tileset” from this menu, and give it any name you want. Browse to find the tanks_sheet.png that you downloaded from this book’s website. Make sure that Tile Width and Tile Height are both 32; keep the Margin and Spacing both at 0.
Select a tile from the tile set on the bottom-right side