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<title>Clipmap</title>

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<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Clipmap</span></span>

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<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="en" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p>In computer graphics, <b>clipmapping</b> is a method of <a href="Clipping_(computer_graphics)" title="Clipping (computer graphics)">clipping</a> a <a href="Mipmap" title="Mipmap">mipmap</a> to a subset of data pertinent to the geometry being displayed. This is useful for loading as little data as possible when <a href="Computer_storage" class="mw-redirect" title="Computer storage">memory</a> is limited, such as on a <a href="Graphics_processing_unit" title="Graphics processing unit">graphics processing unit</a>. The technique is used for <a href="Level_of_detail_(computer_graphics)" title="Level of detail (computer graphics)">LODing</a> in <a href="NVIDIA" class="mw-redirect" title="NVIDIA">NVIDIA’s</a> implementation of <a href="Cone_tracing" title="Cone tracing">voxel cone tracing</a>. The high-resolution levels of the mipmapped scene representation are clipped to a region near the camera, while lower resolution levels are clipped further away.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="MegaTexture">MegaTexture</h2></div>

<p>MegaTexture is a clipmap implementation developed by <a href="Id_Software" title="Id Software">id Software</a>. It was introduced in their <a href="Id_Tech_4" title="Id Tech 4">id Tech 4</a> engine and also appeared in <a href="Id_Tech_5" title="Id Tech 5">id Tech 5</a> and <a href="Id_Tech_6" title="Id Tech 6">id Tech 6</a> before being removed in <a href="Id_Tech_7" title="Id Tech 7">id Tech 7</a>. MegaTexture is a texture allocation technique that uses a single, extremely large <a href="Texture_mapping" title="Texture mapping">texture</a> rather than repeating multiple smaller textures. It is also featured in <a href="Splash_Damage" title="Splash Damage">Splash Damage</a>'s game <i><a href="Enemy_Territory%3A_Quake_Wars" title="Enemy Territory: Quake Wars">Enemy Territory: Quake Wars</a></i>, and was developed by <a href="Id_Software" title="Id Software">id Software</a> former technical director <a href="John_D._Carmack" class="mw-redirect" title="John D. Carmack">John Carmack</a>.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>MegaTexture employs a single large texture space for static terrain. The texture is stored on <a href="Removable_media" title="Removable media">removable media</a> or a computer's hard drive and streamed as needed, allowing large amounts of detail and variation over a large area with comparatively little RAM usage. Depending on the pixel resolution per square meter, covering a large area could require several gigabytes of memory. However, RAM is also filled by the rest of the game and the underlying operating system, limiting the amount available for texturing. As the player moves around the game, different sections of the MegaTexture are loaded into memory. They are then scaled to the correct size and applied to the 3D models of the terrain.

</p><p>Id has presented a more advanced technique that builds upon the MegaTexture idea and virtualizes both the geometry and the textures to obtain unique geometry down to the equivalent of the texel: the <a href="Sparse_voxel_octree" title="Sparse voxel octree">sparse voxel octree</a> (SVO). It works by raycasting the geometry represented by <a href="Voxels" class="mw-redirect" title="Voxels">voxels</a> (instead of triangles) stored in an <a href="Octree" title="Octree">octree</a>. The goal being to be able to stream parts of the octree into video memory, going further down along the tree for nearby objects to give them more details, and to use higher level, larger voxels for farther objects, which give an automatic level of detail (LOD) system for both geometry and textures at the same time. The geometric detail that can be obtained using this method is nearly infinite, which removes the need for faking 3-dimensional details with techniques such as <a href="Normal_mapping" title="Normal mapping">normal mapping</a>. Despite that most voxel rendering tests use very large amounts of memory (up to several GB), Jon Olick of id Software claimed the technology is able to compress such SVO to 1.15 bits per voxel of position data.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup>

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<div class="mw-heading mw-heading2"><h2 id="Virtual_texturing">Virtual texturing</h2></div>

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<p><i><a href="Rage_(video_game)" title="Rage (video game)">Rage</a></i>, powered by the <a href="Id_Tech_5" title="Id Tech 5">id Tech 5</a> engine, uses a more advanced technique called virtual texturing.<sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> Textures can measure up to 128000×128000 pixels<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup> and are also used for in-game models and sprites, etc. and not just the terrain.

</p><p><i><a href="Wolfenstein%3A_The_New_Order" title="Wolfenstein: The New Order">Wolfenstein: The New Order</a></i> and the 2016 version of <i><a href="Doom_(2016)" class="mw-redirect" title="Doom (2016)">Doom</a></i> also use these. <i><a href="Carmageddon%3A_Reincarnation" title="Carmageddon: Reincarnation">Carmageddon: Reincarnation</a></i> also uses virtual texturing, though unlike id's virtual texturing system, which is designed for unique texture-mapping everywhere, their system is designed to use storage space sparingly while still offering good blend of texture variation and resolution.<sup id="cite_ref-6" class="reference"><a href="#cite_note-6"><span class="cite-bracket">[</span>6<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-7" class="reference"><a href="#cite_note-7"><span class="cite-bracket">[</span>7<span class="cite-bracket">]</span></a></sup>

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<ul><li><a href="Surface_caching" class="mw-redirect" title="Surface caching">Surface caching</a></li>

<li><a href="Texture_mapping" title="Texture mapping">Texture mapping</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

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<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external free" href="http://on-demand.gputechconf.com/gtc/2014/presentations/S4552-rt-voxel-based-global-illumination-gpus.pdf">http://on-demand.gputechconf.com/gtc/2014/presentations/S4552-rt-voxel-based-global-illumination-gpus.pdf</a> </span>

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</style><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20080905141523/http://www.shacknews.com/extras/2006/042806_quakewars_qa_1.x">"Enemy Territory: Quake Wars Q&A"</a>. <a href="Shacknews" title="Shacknews">Shacknews</a>. 2006-04-28. Archived from <a rel="nofollow" class="external text" href="http://www.shacknews.com/extras/2006/042806_quakewars_qa_1.x">the original</a> on 2008-09-05<span class="reference-accessdate">. Retrieved <span class="nowrap">2009-08-07</span></span>.</cite></span>

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<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20120301073410/http://s08.idav.ucdavis.edu/olick-current-and-next-generation-parallelism-in-games.pdf">""Jon Olick of id Software siggraph 2008 presentation""</a> <span class="cs1-format">(PDF)</span>. Archived from <a rel="nofollow" class="external text" href="http://s08.idav.ucdavis.edu/olick-current-and-next-generation-parallelism-in-games.pdf">the original</a> <span class="cs1-format">(PDF)</span> on 2012-03-01<span class="reference-accessdate">. Retrieved <span class="nowrap">2024-07-12</span></span>.</cite></span>

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<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="http://mrl.cs.vsb.cz/people/gaura/agu/05-JP_id_Tech_5_Challenges.pdf">"From Texture Virtualization to Massive Parallelization"</a> <span class="cs1-format">(PDF)</span>. <a href="Id_Software" title="Id Software">Id Software</a>. August 2009<span class="reference-accessdate">. Retrieved <span class="nowrap">2011-08-08</span></span>.</cite></span>

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<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20071015163515/http://uk.gamespot.com/video/939982/6176261/id-tech-5-stage-demo-part-1">""Id Tech 5 stage demo""</a>. Archived from <a rel="nofollow" class="external text" href="http://uk.gamespot.com/video/939982/6176261/id-tech-5-stage-demo-part-1">the original</a> on 2007-10-15<span class="reference-accessdate">. Retrieved <span class="nowrap">2024-07-12</span></span>.</cite></span>

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<li id="cite_note-6"><span class="mw-cite-backlink"><b><a href="#cite_ref-6">^</a></b></span> <span class="reference-text"><cite class="citation news cs1"><a rel="nofollow" class="external text" href="http://www.eurogamer.net/articles/digitalfoundry-trials-evolution-tech-interview">"Tech Interview: Trials Evolution"</a>. <i>Eurogamer.net</i>. 28 April 2012.</cite></span>

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<li id="cite_note-7"><span class="mw-cite-backlink"><b><a href="#cite_ref-7">^</a></b></span> <span class="reference-text"><cite class="citation web cs1"><a rel="nofollow" class="external text" href="https://web.archive.org/web/20160307114650/http://www.carmageddon.com/news/nobbys-christmas-message">"Carmageddon | nobby's Christmas message"</a>. Archived from <a rel="nofollow" class="external text" href="http://www.carmageddon.com/news/nobbys-christmas-message">the original</a> on 2016-03-07<span class="reference-accessdate">. Retrieved <span class="nowrap">2024-07-12</span></span>.</cite></span>

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<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.103.3067&rep=rep1&type=pdf">SGI paper from 1998</a></li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20050309050417/http://www.sgi.com/products/software/performer/presentations/clipmap_intro.pdf">SGI paper from 1996</a></li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20070527042158/http://techpubs.sgi.com/library/tpl/cgi-bin/getdoc.cgi?coll=0650&db=bks&srch=&fname=%2FSGI_Developer%2FPerf_PG%2Fsgi_html%2Fch15.html">Description from SGI's developer library</a></li></ul></div><div><div class="zim-footer">

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