Specifications

3
adventure.c Game logic, including the main event loop, helper thread, timing logic, display control logic (motion
and scrolling), and a simple command interpreter (command execution code is in world.c).
assert.c Support for assertions and cleanups as design and debugging aids.
input.c Input control. Provides for initialization and shutdown of the input controller. The version provided
to you supports keyboard control. You must write the support for the Tux controller. This file is not
compiled with the rest of the game and should be used only to test your inputs separately from the
game. Can be compiled stand-alone to test the input device.
modex.c Functions to support use of VGA mode X. Includes things like switching from text mode to mode
X and back, and clearing the screens. Provides a logical view window abstraction that is drawn in
normal memory and copied into video memory using a double-buffering strategy. When the logical
view is shifted, data still on the screen are retained, thus only those portions of the logical view that
were not previously visible must be drawn. Finally, supports mapping from pixelized graphics in
formats convenient to C into drawing a screen at a certain logical position. Relies on photo.c to
provide vertical and horizontal lines from the photo images. Is also compiled stand-alone to create
the tr text mode restoration program.
photo.c Support for reading photo and object image data and mapping them into VGA colors. Also draws
vertical and horizontal lines into graphics buffers for use with scrolling.
text.c Text font data and conversion from ASCII strings to pixelized graphic images of text (you must write
the latter).
world.c Populates game world by setting up virtual rooms, placing objects, and executing commands issued
by the player.
We have also included two stripped binaries to illustrate your end goal. The adventure-demo program is a fully
working version of the game that allows both keyboard and Tux controller input. The input-demo program is a
stand-alone compilation of input.c, again allowing both forms of input. Finally, the mp2photo.c program can be
used to transform 24-bit BMP files into photos for the game, and the mp2object.c program can be used for object
images. Neither tool is needed for your assignment.
The tr Program
The make file provided to you builds both the game and a text-mode-restoration program called tr. The latter program
is provided to help you with debugging. One difficulty involved with debugging code that makes use of the video
hardware is that the display may be left in an unusable (i.e., non-text-mode) state when the program crashes, hangs, or
hits a breakpoint. In order to force the display back into text mode for debugging purposes (or, if you are not running
the program in a debugger, to regain control of your shell), you can run the tr program. Unless you are fairly confident
in your ability to type without visual feedback, we recommend that you keep a second virtual console (CTRL-ALT-F1
through F6) logged in with the command to execute the text restoration program pre-typed, allowing you to simply
switch into that console and press Enter. Using this program is substantially easier than rebooting your machine to put
it back into text mode.
You should also look at the cleanup handlers provided by the assert module (assert.h and assert.c). These
cleanup handlers provide support for fatal exceptions, putting the machine back into a usable state when your program
crashes. However, there may be instances and problems not covered by the handlers, and GDB can stop the program
before the handlers are invoked, leaving the machine in an unusable state until you restore text mode with tr.
Mode X and Graphic Images
Mode X is a 256-color graphics mode with 320x200 resolution. It was not supported by the standard graphics routines
that came with the original VGAs, but was supported by the VGA hardware itself, and was quickly adopted as the stan-
dard for video games at the time because of certain technical advantages over the documented 256-color mode (mode
13h, where the ‘h’ stands for hexadecimal). In particular, mode X supports multiple video pages, allowing a program
to switch the display between two screens, drawing only to the screen not currently displayed, and thereby avoiding the
annoying flicker effects associated with showing a partially-drawn image. This technique is called double-buffering.
Each pixel in mode X is represented by a one-byte color value. Although only 256 colors are available in mode X, the
actual color space is 18-bit, with 6-bit depth for red, green, and blue saturation. A level of indirection is used to map