Game engine recreation

<h2 id="motivation">Motivation</h2>
Game engine recreations are made to allow the usage of classical games with newer <a href="/facts/Operating_system/8XTuvMh2">operating system</a> versions, recent hardware or even completely different operating systems than originally intended. Another motivation is the ability to fix engine <a href="/facts/Bug_(computing)/I1uSXySv">bugs</a> which is often hard or impossible with the original engines (with notable exceptions, see <a href="/facts/Community_patch/CwquC8br">community patch</a>) once a software has become unsupported, with the <a href="/facts/Source_code/o9J6Jv23">source code</a> not available.

<h2 id="methods">Methods</h2>
<h3>Top down</h3>
See also: <a href="/facts/High-level_emulation/yhgnIfBy">High-level emulation</a>
When game engine recreations are made in a <a href="/facts/Top-down_and_bottom-up_design/MvtTkA3x">top down development methodology</a>, in the first step the general game's functionality is programmed and the structure is defined. Then, in later steps, the resulting engine is adapted to the specific detail behaviour of the original game, often by reverse engineering, debugging and profiling the original. An example is <a href="/facts/OpenRA/WJXXEA3A">OpenRA</a> based on specifications contributed by the community by <a href="/facts/Clean_room_design/5t2ewW61">clean-room re-implementations</a><a class="footnote-ref" id="fnref:1" href="#fn:1">1</a> without dis-assembling the original executable, which result in game engines whose behavior differs from the original.<a class="footnote-ref" id="fnref:2" href="#fn:2">2</a> Another example is the <a href="/facts/Total_Annihilation/o8Xeq9v9">Total Annihilation</a> engine remake Spring Engine, which resulted in being used for many more games. Typically, this approach results in an approximation of the original behaviour only and not a "<a href="/facts/Clock_cycle/9UfTzGHx">clock cycle</a> wise" identical behaviour. On the positive side, this approach typically yields working code more quickly, and the resulting source code is less tied to a single game, allowing it to be reused as a general engine for other games.

<h3>Bottom up</h3>
See also: <a href="/facts/List_of_commercial_video_games_with_available_source_code/As3uTTL9">List of commercial video games with available source code § Games with reconstructed source code</a>
Unlike Top down game engine recreations, bottom up dis-assembled/decompiled versions for a specific game are often able to replicate the behaviour of the original exactly. In these cases, the game core is recreated bottom up with <a href="/facts/Reverse_engineering/pmJCV7J7">reverse engineering</a> of the original <a href="/facts/Disassembler/4PR39BbK">dis-assembled</a> binary executable, CPU instruction for instruction. In the development phase this has the disadvantage that for a long time no running prototype exists. Also on the negative side, the resulting code is very specifically tied to this single game, often ugly ("pseudo-<a href="/facts/Assembly_language/7XuV0cla">assembly code</a>"<a class="footnote-ref" id="fnref:3" href="#fn:3">3</a><a class="footnote-ref" id="fnref:4" href="#fn:4">4</a>), and can hardly be reused as general game engine. Examples are <a href="/facts/Dungeon_Master_(video_game)/dS4RdQJN">CSBWin</a> or <a href="/facts/OpenTTD/6ABJEuBz">OpenTTD</a>. Most often, the result is also not called "game engine" but "game recreation" or "game clone". <a href="/facts/MAME/4VkQ6d9z">MAME</a> is an example of a video game engine emulation project which also follows this philosophy for accurate representation of the games.

<h3>Source code ports</h3>
See also: <a href="/facts/Source_port/6z2qbY4I">Source port</a> and <a href="/facts/List_of_commercial_video_games_with_available_source_code/As3uTTL9">List of commercial video games with available source code</a>
Occasionally, as was the case with some of the engines/game cores in <a href="/facts/ScummVM/6cqwuU9o">ScummVM</a>, the original developers have helped the projects by supplying the original <a href="/facts/Source_code/o9J6Jv23">source code</a> (those can be then called <a href="/facts/Source_port/6z2qbY4I">source ports</a>). This is the best case, optimal for accuracy and minimizing the effort. An example is <a href="/facts/Beneath_a_Steel_Sky/nDW3RuYC">Beneath a Steel Sky</a>.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a><a class="footnote-ref" id="fnref:6" href="#fn:6">6</a>

<h2 id="alternatives">Alternatives</h2>
<a href="/facts/Emulator/FMHE8qDj">Emulation</a> of classical systems or operating systems is an alternative to an engine recreation; for instance <a href="/facts/DOSBox/Du2egHYo">DOSBox</a> is a notable emulator of the <a href="/facts/IBM_PC/yhcJGMPL">PC</a>/<a href="/facts/MS-DOS/fVrrz1uN">MS-DOS</a> environment. <a href="/facts/Static_recompilation/trAQq97A">Static recompilation</a> is another approach based on the original binary <a href="/facts/Executable/VSst9eLA">executable</a>, potentially leading to better performance than emulation; an example is the 2014 <a href="/facts/ARM_architecture/SALsYA79">ARM</a> architecture version of <a href="/facts/StarCraft/xkQlTnGP">StarCraft</a> for the <a href="/facts/Pandora_(console)/D2og4tqV">Pandora</a>.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a><a class="footnote-ref" id="fnref:8" href="#fn:8">8</a><a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> Another alternative are <a href="/facts/Source_port/6z2qbY4I">source ports</a> for the rare cases that the source code is available; examples are <a href="/facts/Jagged_Alliance_2/1Gd551tg">Jagged Alliance 2</a><a class="footnote-ref" id="fnref:10" href="#fn:10">10</a> or <a href="/facts/Homeworld/hEQhmJ6Q">Homeworld</a><a class="footnote-ref" id="fnref:11" href="#fn:11">11</a><a class="footnote-ref" id="fnref:12" href="#fn:12">12</a><a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> (more examples in the <a href="/facts/List_of_commercial_video_games_with_available_source_code/As3uTTL9">List of commercial video games with available source code</a>).

<h2 id="see-also">See also</h2>
<ul>
<li>Video games portal</li></ul>
<ul><li><a href="/facts/List_of_game_engine_recreations/XNqMFtFe">List of game engine recreations</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">"OpenRA/OpenRA". GitHub. Retrieved 2018-08-30. <a href="https://github.com/OpenRA/OpenRA/wiki/FAQ#is-that-legal" target="_blank">https://github.com/OpenRA/OpenRA/wiki/FAQ#is-that-legal</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Development-Goals openra on github.com <a href="https://github.com/OpenRA/OpenRA/wiki/Development-Goals" target="_blank">https://github.com/OpenRA/OpenRA/wiki/Development-Goals</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Release: Starcraft on pyra-handheld.com "As you can see it doesn't look much different from x86 disassembly, the only difference is that you can compile it for other 32bit archs (there is no way it would work on 64bit.." <a href="https://pyra-handheld.com/boards/threads/starcraft.73844/page-3#post-1292053" target="_blank">https://pyra-handheld.com/boards/threads/starcraft.73844/page-3#post-1292053</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Chaos Strikes Back for Windows (and Linux, MacOS X, Pocket PC) on Dungeon Master Encyclopedia "About 120,000 lines of pseudo-assembly language. Crazy thing to do. But it works." <a href="http://dmweb.free.fr/?q=node/851" target="_blank">http://dmweb.free.fr/?q=node/851</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"Latest Developments". ScummVM.org. August 2, 2012. Retrieved July 14, 2013. Support for Beneath a Steel Sky, made possible thanks to Revolution Software supplying us with the original assembly source code! <a href="http://www.scummvm.org/news/20030802/" target="_blank">http://www.scummvm.org/news/20030802/</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Source code "Source code for Beneath a Steel Sky in Assembly language (415,225 bytes) xxxx" (2005) <a href="http://www.classicdosgames.com/game/Beneath_a_Steel_Sky.html" target="_blank">http://www.classicdosgames.com/game/Beneath_a_Steel_Sky.html</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Steinlechner, Peter (2014-03-10). "Starcraft für ARM-Handheld kompiliert" (in German). golem.de. Retrieved 2014-03-25. <a href="http://www.golem.de/news/open-pandora-starcraft-fuer-arm-handheld-kompiliert-1403-105031.html" target="_blank">http://www.golem.de/news/open-pandora-starcraft-fuer-arm-handheld-kompiliert-1403-105031.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">notaz (2014-03-04). "StarCraft". repo.openpandora.org. Retrieved 2014-03-26. <a href="http://repo.openpandora.org/?page=detail&app=package.starcraft" target="_blank">http://repo.openpandora.org/?page=detail&app=package.starcraft</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">notaz (2014-03-04). "Starcraft". openpandora.org. Archived from the original on 2015-12-10. Retrieved 2014-03-29. The "no source, no port" rule is not completely true, you can get something similar (but not the same) as a port through static recompilation. Similar stuff was done several times by M-HT for some DOS games. The game was also converted for Android with somewhat similar approach. <a href="https://web.archive.org/web/20151210192115/https://boards.openpandora.org/topic/15820-starcraft/" target="_blank">https://web.archive.org/web/20151210192115/https://boards.openpandora.org/topic/15820-starcraft/</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Burnes, Andrew (2004-02-25). "Jagged Alliance 2 Source Code To Be Bundled With Wildfire". ign.com. Archived from the original on January 8, 2013. Retrieved 2012-12-23. <a href="https://web.archive.org/web/20130108130325/http://ve3d.ign.com/articles/news/18050/Jagged-Alliance-2-Source-Code-To-Be-Bundled-With-Wildfire" target="_blank">https://web.archive.org/web/20130108130325/http://ve3d.ign.com/articles/news/18050/Jagged-Alliance-2-Source-Code-To-Be-Bundled-With-Wildfire</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Largent, Andy (2003-10-08). "Homeworld Source Code Released". Inside Mac Games. Archived from the original on 2013-10-12. Retrieved 2011-01-10. <a href="https://web.archive.org/web/20131012012745/http://www.insidemacgames.com/news/story.php?ArticleID=8516" target="_blank">https://web.archive.org/web/20131012012745/http://www.insidemacgames.com/news/story.php?ArticleID=8516</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">"Archived copy". Archived from the original on 2012-08-04. Retrieved 2014-03-30.{{cite web}}: CS1 maint: archived copy as title (link) <a href="https://archive.today/20120804163454/http://www.homeworldsdl.org/LICENSE.txt" target="_blank">https://archive.today/20120804163454/http://www.homeworldsdl.org/LICENSE.txt</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">pandorapress staff (2011-06-23). "Game of the Week #3 – Homeworld SDL". pandorapress.net. Retrieved 2013-04-24. [...] released port of HomeworldSDL. [...]enables your Pandora to experience the excellent work done by the guys at HomeworldSDL. <a href="http://pandorapress.net/2011/06/23/game-of-the-week-3-homeworld-sdl/" target="_blank">http://pandorapress.net/2011/06/23/game-of-the-week-3-homeworld-sdl/</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
</ol>

Game engine recreation open-in-new

Game engine recreation