Gdc09 Minimissile

MiniGames Rebuilding Three Classic Joe Linhoff Eugene Jarvis Darren Torpey

Missile Command, 1980 Atari

Learning Objectives

dynamic object management with lists

C-style polymorphism

screen to world, world to screen coordinate

Dynamic Objects

Don't know how many enemy missiles there will be at any time

Missiles can split (MIRVs)

Don't know how many player missiles there will be at any time

The static ways will not work

Lists are the backbone of game development

Doubly linked lists make it easy and quick to unlink nodes

Dynamic Infrastructure init body final

Good code construction requires guaranteed init and final

Init

sets up all list heads

Final

runs through & frees all lists

The lists 'own' the object

write code such that only way to object is through list; do not keep any other copies

always test pointers before use

generally: one owner for every resource

Game Controller Class Owns Game Objects

Simplifies collisions and other multi-type operations

init is in constructor

initializes all lists by making them list heads

final is in 'final'

zaps all remaining objects in lists

not destructor b/c we want more control

idea is to clean up after yourself

// JFL 13 Aug 08 Game::Game(chr *name) : qeUpdateBase(name,0,GAMEID_GAME) { this->name = qeObjName(this->_oShared); LLMakeHead(&this->listOfGameThings); LLMakeHead(&this->listOfWorlds); LLMakeHead(&this->listOfBuildings); LLMakeHead(&this->listOfPlayers); LLMakeHead(&this->listOfBadGuys); LLMakeHead(&this->listOfPlayerProjs); LLMakeHead(&this->listOfBadGuyProjs); } // Game::Game() // JFL 18 Aug 08 void Game::final() { // don't call directly, use objRemove() Game *game; if((game=Game::instance)) { gameZapList(&game->listOfBadGuyProjs); gameZapList(&game->listOfPlayerProjs); gameZapList(&game->listOfBadGuys); gameZapList(&game->listOfPlayers); gameZapList(&game->listOfBuildings); gameZapList(&game->listOfWorlds); gameZapList(&game->listOfGameThings); delete game; // free the C++ object Game::instance=0; // reset pointer } } // Game::final()

Game Objects

Constructors must setup their own node

LLMakeNode() here

part of init

Destructor not explicitly needed

// JFL 14 Aug 07 World::World(chr *name) { szcpy(this->name,sizeof(this->name),name,0); LLMakeNode(this,GAMEID_WORLD); SET3(this->xyzMin,-110,0,0); SET3(this->xyzMax,110,200,0); } // World::World() // JFL 14 Aug 07 int World::draw(void) { qefnDrawGrid(50,10); qefnDrawAxes(1); return 0; } // World::draw()

Owners Must Always Guarantee Cleanup

Game::final()

runs through all the lists of objects it owns and zaps them

after all the objects it owns are zapped, it deletes itself and zeros its Singleton instance pointer

not called directy, Game derives from qeUpdateBase and call to objRemove() causes engine to call final() when it's safe

// JFL 18 Aug 08 void Game::final() { // don't call directly, use objRemove() Game *game; if((game=Game::instance)) { gameZapList(&game->listOfBadGuyProjs); gameZapList(&game->listOfPlayerProjs); gameZapList(&game->listOfBadGuys); gameZapList(&game->listOfPlayers); gameZapList(&game->listOfBuildings); gameZapList(&game->listOfWorlds); gameZapList(&game->listOfGameThings); delete game; // free the C++ object Game::instance=0; // reset pointer } } // Game::final()

Zap & Zap List

Use while when unlinking

Zap

unlink

calls destructor

frees memory

'zap' b/c it's descriptive, short, not generally used, and cool

// JFL 25 Jan 09 int gameZapList(LLNode *head) { LLNode *n; while((n=head->next)&&n->t) gameZap(n); return 1; // nonzero return assumed } // gameZapList() // JFL 25 Jan 09 int gameZap(LLNode *n) { // unlink the game object LLUnlink(n); // call destructor for game objects switch(n->t) { case GAMEID_INPUT:((Input*)n)->~Input();break; case GAMEID_CAMERA:((Camera*)n)->~Camera();break; case GAMEID_HUD:((HUD*)n)->~HUD();break; case GAMEID_WORLD:((World*)n)->~World();break; case GAMEID_BUILDING:((Building*)n)->~Building();break; case GAMEID_PLAYER:((Player*)n)->~Player();break; case GAMEID_PROJ:((Proj*)n)->~Proj();break; case GAMEID_BADGUY:((BadGuy*)n)->~BadGuy();break; default: BRK(); // add handler for type } // switch // free the memory delete (qe*)n; return 1; // nonzero return assumed } // gameZap()

Simple Doubly Linked C-Style Polymorphic Lists