Resources in HTML TADS

What is a "resource"?

If you're a Macintosh or Windows system programmer (or you've done any other type of graphical user interface programming), you're probably familiar with the term "resource," meaning a bit of data, usually binary, that's external to a program, and which is loaded and used by the program as it runs. Resources in this context are used for things such as icons, bitmaps, menu definitions, and other types of initialized binary data that would be inconvenient to type in to a C program directly; resources are also used to externalize things such as strings, so that they can be changed without recompiling the program (which is useful when translating a program to a different national language, for example). On most GUI systems, the operating system provides a set of tools, programmatic interfaces, and file format definitions for manipulating resources.

HTML TADS uses the term "resource" for a similar concept, although the implementation is quite different. HTML TADS resources are not implemented using operating system resources. To avoid any confusion, keep in mind that normal operating system resources are never used in an HTML TADS context.

HTML TADS allows the game author to incorporate certain types of binary data, such as JPEG, PNG, and MNG images, into a game. With normal HTML in a normal Web browser, these objects are referenced using URL's ("Uniform Resource Locators," the filename-like strings that identify web pages and graphics; URL's usually look something like "").

HTML TADS is not a normal browser, and it doesn't interpret object references as URL's. Instead, it uses resources.

Specifying resource names

A game author uses a resource by referring to the resource from an HTML tag in the game's text. When the game displays the tag, HTML TADS loads the resource and displays it as specified by the tag.

As mentioned earlier, with normal HTML, this type of reference is simply a URL that points to a file stored on a web server. With HTML TADS, the reference is instead a resource name.

At its simplest, a resource name is very much like a relative URL -- that is, one which is specified relative to the address of the page that references it, and therefore doesn't contain any protocol or absolute path prefix. This type of URL reference might look like this:

   <IMG SRC="background.jpeg">

This tells the browser to load an image from a file called "background.jpeg", looking in the same location as the current page.

HTML TADS resource references work very much like this, because they're simply filenames. The location of the "current page" for HTML TADS is always the directory that contains your .GAM file or .t3 file.

For example, support you're running Windows 95, and the compiled version of the game you're working on is called C:\TADS\GAMES\MYGAME.GAM. The root location where HTML TADS will start looking for resource files is the directory containing the .GAM file, C:\TADS\GAMES. Now, suppose you use this tag in your game text:

    <IMG SRC="picture.jpg">

HTML TADS will load the image from the file C:\TADS\GAMES\PICTURE.JPG, since it looks for the file you specify in the directory containing the .GAM or .t3 file.

Note that you can never refer to resources across the internet - you can't use "http:" or "ftp:" paths, for example. You can only refer to resources that are on the local computer's hard disk.

Relative Paths

The name of a resource can include a "relative path," using roughly the same format as a relative URL. Since HTML TADS doesn't interpret actual URL's, you can't start a resource name with "http://" as you would an absolute URL; instead, you use a path that's relative to the current location (which is always the directory containing the .GAM or .t3 file), just as you could use an URL relative to the current page.

HTML TADS resource names that use relative paths always use slashes for the path separator characters, regardless of what conventions your operating system uses. TADS internally converts these paths into appropriate filenames for the local system. Because resource names always use a uniform notation, regardless of the type of operating system you're using, you don't have to worry about changing your game to make it run on other operating systems.

Suppose you're running on a Macintosh, and your compiled game file is called Macintosh HD:TADS:Games:MyGame.gam. Now suppose your game displays this tag:

    <IMG SRC="pics/skull.png">

HTML TADS will convert this to a Macintosh filename, treating it as a path relative to the folder containing the .GAM or .t3 file, so it will look for a file called Macintosh HD:TADS:Games:pics:skull.png.

Case Sensitivity

You need to be careful about using upper- and lower-case letters in your resource names. HTML TADS does not itself treat case as significant, but some file systems (notably Unix) do. If you're developing your game on an operating system with case-sensitive filenames, you'll need to use the exact mixture of upper- and lower-case letters in your resource references as you do in the actual filenames.

Note that the HTML TADS resource mechanism is not case-sensitive. So, if you develop a game on a system with case-sensitive filenames, and then you bundle your resources into the .GAM or .t3 file for distribution, the resource names will not distinguish case in the version your players receive. While this may appear at first glance to simplify things for you, it actually can create a problem: if you have two resources whose names differ only in case, HTML TADS will treat them as separate resources as long as they're in external files, but it will not be able to tell them apart after you bundle them into the .GAM or .t3 file. So, if you're developing on a case-sensitive operating system, be careful that your resource names are all unique irrespective of case.

Note that resource names only need to be unique within a directory. You may still want to avoid using the same resource name for different files in different directories, because of the confusion it might create for you, but HTML TADS will distinguish files with the same name based on their paths, regardless of whether you're using external files or bundled resources.

Image types

HTML TADS supports two static image formats: JPEG and PNG. Ideally, HTML TADS would support only one format, since this would make it easier to port HTML TADS to new operating systems; however, no single image format adequately addresses the full range of needs for storing images. Fortunately, the JPEG and PNG formats complement one another very well, so between the two, most needs should be met.

In addition to the static image formats, HTML TADS supports MNG, an animated image format.

Note that the GIF format is not supported. Although GIF is a widely deployed and popular image format, I chose not to support it in HTML TADS due to patent licensing restrictions on the GIF data compression system. PNG provides all of the benefits of GIF (and more), without the onerous restrictions encumbering GIF, and is becoming widely supported.

You can learn more about the PNG format at . This site includes information about tools that support PNG. Even if the graphics software you prefer to use doesn't support this format, conversion tools are available that produce PNG files from files in the other popular formats.

Information about the MNG format can be found at the MNG web site.

Sound types

HTML TADS supports four sound formats: MIDI, WAV, MPEG Audio 2.0 (layers I, II, and III, also known as MP1, MP2, and MP3, respectively), and Ogg Vorbis digital audio. Refer to HTML TADS Sounds and Music for information on the sound features in HTML TADS.

We recommend using Ogg Vorbis over MP3. Ogg is generally considered a superior format in terms of playback quality and compression ratio, and it's a fully open-source format. Some Linux Multimedia TADS players don't support MP3 due to intellectual property entanglements, but all platforms support Ogg.

Filename suffixes

HTML TADS determines the type of object that a resource contains based on the resource's suffix. You must always use an appropriate suffix when naming a resource. Here are the valid suffixes:

Note that the suffix always begins with a period.

Some of the types are associated with multiple suffixes. For example, JPEG images can use the suffixes .JPG, .JPE, and .JPEG. There's no difference between the suffixes in these cases; the variations are allowed simply because the different suffixes are all in widespread use.

Embedding resources in a .GAM or .t3 file

To make it easy to distribute a game, you can embed all of your resources into your compiled .GAM or .t3 file. Once the resources are embedded, you only have to distribute the compiled game file - you don't have to distribute all of the JPEGs and PNGs and OGGs and so on individually. (This also makes it a little more work for players to "cheat" by browsing the images in your game; the temptation could be overwhelming if you were to distribute your game with a set of .JPG files.)

Since you may not want to go to the trouble of embedding your resources in the .GAM or .t3 file while you're developing your game (since you'll probably be recompiling the game frequently), the resource embedding mechanism is strictly optional. Most authors will want to use external files while developing a game, and then bundle everything into the compiled game file when building the distribution version of the game. You generally won't want to bundle resources into the compiled game file while working on the game, since you'd need to apply the extra resource bundling step each time you compile the game.

Note that, apart from the possible differences in case sensitivity between your operating system and the HTML TADS resource mechanism, you won't have to make any changes in your game to switch between using external files and bundled resources. The bundling mechanism stores the resources using the same name they'd have if they were external files.

To embed resources into a .GAM or .t3 file, you use the TADS resource manager. For TADS 2, this is called TADSRSC; for TADS 3, it's t3res.

The simplest way of using the resource manager is to store all of your resources in one or more subdirectories of the directory containing the compiled game file. Since relative paths work best for external files if you're working this way, you'll probably want to arrange your resources into this type of directory structure anyway.

Suppose you have your resources in two subdirectories of the directory containing your .GAM file; the subdirectories are called Rooms and Objects. Using external files, you'd refer to resources in one of these directories using a tag like this:

    <IMG SRC="Rooms/Cave.jpeg">

To bundle all of these resources into your .GAM file, you'd first compile your game as normal, then you'd run TADSRSC or t3res on it:

tadsrsc mygame.gam Rooms Objectsfor TADS 2
t3res mygame.t3 Rooms Objectsfor TADS 3

This invokes the resource manager, and tells it to store every file in the Rooms and Objects subdirectories in your .GAM or .t3 file. The resource tool stores these resources using the same names they'd have if they were external files, so your cave picture gets stored as a resource called Rooms/Cave.jpeg in the game file.

Note that you need to run TADSRSC/t3res each time you compile your game, because the TADS compiler overwrites any existing copy of your .GAM/.t3 file each time you compile your game.

When you refer to a resource, HTML TADS always looks for the resource in the .GAM or .t3 file first. If it can't find a resource in the game file, it looks for an external file.

Using External Resource Files for Multiple Configurations

If you're planning to distribute your game on CD-ROM, or better yet DVD-ROM, you're probably not too concerned about how big your game is going to be when you bundle together all of your image and sound files. However, if you're planning to distribute your game over the internet, you probably will be concerned about the total size of your distribution files, and you may want to accommodate players who have slow network connections.

One approach to accommodating players who don't want to download very large game files is simply to be conservative in your use of graphics and sound resources. HTML TADS allows you to use graphics and sounds as heavily or lightly as you like; if you use graphics and sound in only a few places, where they will provide the greatest impact, you can keep your total distribution size within reason.

An alternative approach that some game authors may wish to consider is to offer their games in multiple configurations. The idea is that you offer your game in two or more pieces: a "core" file that everyone downloads, which includes the .GAM or .t3 file plus the minimum set of resources; and one or more add-on files that people can download at their option, and which contain additional resources that you consider optional. Alternatively, you could provide one file that contains full-quality versions of your resources, and a separate file that contains lower-quality (using fewer colors, for example, or lower resolution digitized sound) and therefore smaller versions of the same resources; people with slow connections would be able to download the lower-quality version if they wanted, but those who had a fast network connection (or lots of patience) would still be able to get the full-quality version.

To facilitate these types of configuration options, HTML TADS lets you put your resources into separate files from your .GAM/.t3 file. With external resource files, you can still bundle a group of files into a single file for easier distribution, but now they're separated from the .GAM/.t3 file for more versatile configuration.

TADS 2 Note: the external resource file mechanism requires TADSRSC version 2.2.4 or higher.

Creating External Resource Files

You prepare a secondary resource file using the same resource manager as you use to add resources to your .GAM/.t3 file. The only difference is that, in order to create your external resource file in the first place, you must use the -create option on the resource manager command line:

tadsrsc -create mygame.rs0 -add Roomsfor TADS 2
t3res -create mygame.3r0 -add Roomsfor TADS 3

The -create option tells the resource manager to create a new file rather than look for an existing file. You would never use this option with a .GAM or .t3 file, of course, because the TADS compiler creates the game file before you add resources to it; with a separate resource file, there's no prior compilation step, so you need to create the file directly with the resource manager the first time you use it.

How HTML TADS Loads External Resource Files

Whenever HTML TADS loads a game, it looks to see if there are any files in the same directory as the game with the same name as the game and the suffix ".rsN" (for TADS 2) or ".3rN" (for TADS 3), where N is a digit from 0 to 9. For example, if your game is called GOLD.GAM, HTML TADS will look in the same directory as GOLD.GAM for files called GOLD.RS0, GOLD.RS1, GOLD.RS2, and so on. For a TADS 3 game called GOLD.T3, the interpreter would look for GOLD.3R0, GOLD.3R1, GOLD.3R2, and so on. HTML TADS will open each file and add its resources to the resources in the .GAM/.t3 file.

A resource in an external resource file overrides a resource of the same name in the .GAM or .t3 file. This allows you to place your minimum, core set of resources in the game file, so that everyone who downloads your game has at least that minimal set of resources, and then provide an "upgrade" resource file to players that don't mind the additional download. Since the separate resource file overrides the .GAM file resources, players who download the additional file will automatically see the upgraded resources.

If resources with the same name appear in multiple external resource files, the resource in the file with the highest suffix number overrides any conflicting resources. For example, if MYGAME.RS3 and MYGAME.RS1 both contain a resource with the same name, the resource in MYGAME.RS3 is used, and the one in MYGAME.RS1 is ignored. (Likewise for TADS 3 files: MYGAME.3R3 overrides MYGAME.3R1.)

Note that the player can optionally specify the path to the external resource files. By default, HTML TADS looks for resource files in the same directory that contains the .GAM file. If, for some reason, the player can't put resource files into the same directory (which might be the case if some of the files are distributed on read-only media such as CD-ROM, while others are distributed for installation on the player's hard disk), the player can specify another directory for resource files. To do this, the player uses the -respath command-line option when invoking HTML TADS:

    htmltads -respath d:\gold\res gold.gam
This tells HTML TADS to run GOLD.GAM from the current directory, but to look for GOLD.RS0, GOLD.RS1, and so on in the directory D:\GOLD\RES instead of in the current directory.

An Example of Using External Resource Files

Numerous configurations are possible using this mechanism. As an example, one use of external resource files would be to provide a high-quality version of your sound effects for people that didn't mind large files, and a lower-quality version for people with slow network connections. To do this, you'd sample your sound effects at full quality, then use the sound tool of your choice to produce smaller versions (for example, by reducing the quantization, or reducing a stereo recording to mono). Put the high-quality sounds in the directory AudioHQ, and put the more compact versions in AudioLQ. Now you can produce a pair of resource files for the sound effects:

    tadsrsc -create mygame.rs0 -add AudioLQ
    tadsrsc -create mygame.rs1 -add AudioHQ

We've intentionally placed the higher-quality resources in the .RS1 file, so that if a player should happen to have both resource files installed, the higher-quality ones will be used. (As described earlier, the resource mechanism automatically picks the resource in the highest-numbered resource file if the same resource name appears in multiple external resource files.)

When you distribute your game, you would put together two zip files. The first contains MYGAME.GAM and MYGAME.RS0; this is the large version, for people with fast network connections. The second contains MYGAME.GAM and MYGAME.RS1; this is the compact version.

Embedded Resources and TADS 2 .GAM File Compatibility

HTML TADS uses the same TADS .GAM file format as previous versions of TADS (file format version "C"), so games that you compile for HTML TADS can be read by older versions of the interpreter. However, note that embedded HTML resources do use a new resource type, which older interpreters will not recognize. Therefore, if you embed resources directly into your .GAM file, players that play the game with a character-mode interpreter must have at least version 2.2.3. If you do not embed resources directly in your .GAM file, this restriction does not apply; you may want to use external resource files, as described above, if this is of concern to you.