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Programs

How to run a game, and how to turn one into a program of its own. Building the engine is in engine.

xgecli

xgecli                       # loads "pong"
xgecli breakout              # a bare name gets ".xml" added
xgecli path/to/pong.xml      # a name with an extension is used as given
xgecli pong -w sdl2 -x tinyxml2 -a none
xgecli galaxian --record     # play, then write what was played into the file as its <demo>
xgecli pong --generate windows-cpp -o out/pong
Option Means
game, -g, --game the game, bare or with -g (not both). Default pong
-w, --window sfml3 (default), raylib, sdl2, opengl
-x, --xml xerces (default), tinyxml2, pugixml, rapidxml
-a, --audio sfml3 (default), raylib, sdl2, none
--record play from a new seed; when the window closes, write the play into the game file as its <demo>
--generate <target> write the game out as a program instead of playing it (below)
-o, --output <dir> where --generate writes (default <game>-<target>); an error without --generate
-h, --help usage, listing the libraries this build has

Options. A short option takes its value attached or spaced (-gpong, -g pong); a long one needs the space (--game pong, never --game=pong). Names are not case sensitive, and each option may be given once. Only libraries this build has can be named (backends). --record and --generate are long only and do not go together.

Finding the game. In order: as given; its file name in the working directory; descriptions/ of the games folder. The games folder is the first folder holding both descriptions/ and assets/, looked for in the working directory, the program's folder and the folder above, each itself and then its games/. The program then makes the games folder its working directory, so it runs from anywhere and asset paths (assets/paddle.jpg) are relative to it (engine/folder.h).

Output. It prints the file, window, XML and sound library it chose, one a line. A game that will not load (schema, an expression, a name it does not have) prints a message saying where, and exits.

xgegui

The Qt 6 application, built only when Qt is found.

  • xgegui pong opens a game; with none, a file dialog in games/descriptions/.
  • The game is drawn beside a tree of its data, which can be edited while it runs. Play, Pause, Step and Reset drive it; Options picks the video, XML and sound libraries.
  • A game that will not load is shown as a message, and the program carries on.
  • The game is drawn as large as fits, keeping its proportions. A bar under it shows the defined size, its scale and the percent shown, with smaller, 100% and bigger buttons.
  • One window or two: the game can have its own window, opened by the chosen library.

Design: gui.

In C++ the libraries are chosen with Game(file, XmlBackend) and Engine(game, WindowBackend, AudioBackend).

Generating a program

xgecli pong --generate windows-cpp                 # writes pong-windows-cpp/
xgecli pong --generate windows-cpp -o out/pong     # or into the folder named

This writes a C++ program on SFML 3 that is the engine with the game built in, so it plays exactly as xgecli does. The engine first loads the game as for play (a game that will not load is not generated), then the XSLT stylesheets in games/generators/windows-cpp/ (run by libxslt) write:

Written By What
source/<game>.cpp merge.xsl, then data.xsl the game as the engine's own GameData (game/data.h), a line of C++ per tag, with the kit and every from= worked out first. One function returns it (pongMinGame())
source/game_parts.h copied from modules/ the small functions those lines call
source/main.cpp, CMakeLists.txt, README.md, .gitignore program.xsl makes the Game, an SFMLWindow and an SFMLAudio and runs Engine::loop; the build finds or fetches SFML 3 and lunasvg
engine/ listed in engine.xml the engine's files, copied unchanged from xge/lib/ of the repository xgecli was built from, less XML reading and the other libraries
assets/, LICENSE xgecli the pictures and font it uses (with a font's licence), the repository's licence

xgetest-generated (cmake --build build --target xgetest-generated, never in an ordinary build) generates every game, compares its compiled data with what readGame reads from the file field by field, and plays the two side by side frame by frame. Without libxslt, xgecli is built without --generate and says so. Design: generator.