{"action":"created","issue":{"url":"https://api.github.com/repos/PixarAnimationStudios/OpenSubdiv/issues/168","labels_url":"https://api.github.com/repos/PixarAnimationStudios/OpenSubdiv/issues/168/labels{/name}","comments_url":"https://api.github.com/repos/PixarAnimationStudios/OpenSubdiv/issues/168/comments","events_url":"https://api.github.com/repos/PixarAnimationStudios/OpenSubdiv/issues/168/events","html_url":"https://github.com/PixarAnimationStudios/OpenSubdiv/issues/168","id":15082635,"number":168,"title":"OpenSubdiv showed cracks after displacement","user":{"login":"shengfuintel","id":3935335,"avatar_url":"https://avatars.githubusercontent.com/u/3935335?v=3","gravatar_id":"","url":"https://api.github.com/users/shengfuintel","html_url":"https://github.com/shengfuintel","followers_url":"https://api.github.com/users/shengfuintel/followers","following_url":"https://api.github.com/users/shengfuintel/following{/other_user}","gists_url":"https://api.github.com/users/shengfuintel/gists{/gist_id}","starred_url":"https://api.github.com/users/shengfuintel/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/shengfuintel/subscriptions","organizations_url":"https://api.github.com/users/shengfuintel/orgs","repos_url":"https://api.github.com/users/shengfuintel/repos","events_url":"https://api.github.com/users/shengfuintel/events{/privacy}","received_events_url":"https://api.github.com/users/shengfuintel/received_events","type":"User","site_admin":false},"labels":[{"url":"https://api.github.com/repos/PixarAnimationStudios/OpenSubdiv/labels/bug","name":"bug","color":"FF9933"},{"url":"https://api.github.com/repos/PixarAnimationStudios/OpenSubdiv/labels/question","name":"question","color":"DDDDDD"}],"state":"open","locked":false,"assignee":null,"milestone":null,"comments":3,"created_at":"2013-06-03T18:55:25Z","updated_at":"2015-04-17T18:06:33Z","closed_at":null,"body":"OpenSubdiv claimed water tight tessellation. I did some experiments to add displacement to check if OpenSubdiv is still water tight after displacement. I modified glslPatchCommon.glsl like the following:\r\n\r\n#ifndef OSD_DISPLACEMENT_CALLBACK\r\n#define OSD_DISPLACEMENT_CALLBACK  output.v.position.xyz += 0.4 * output.v.normal;           \\\r\n                                  WorldPos = output.v.position.xyz;\r\n#endif\r\n\r\nBasically add a constant displacement along normal. However, I did see some cracks, see one example below:\r\n\r\n![gap](https://f.cloud.github.com/assets/3935335/601383/bd7a4bac-cc7e-11e2-9e8a-35c0bdd83954.jpg)\r\n\r\nAny idea why it happens?\r\n\r\nI don't think there is an option to turn on/off water tight tessellation. Is it correct?\r\n\r\nThanks\r\n\r\nSheng"},"comment":{"url":"https://api.github.com/repos/PixarAnimationStudios/OpenSubdiv/issues/comments/94041339","html_url":"https://github.com/PixarAnimationStudios/OpenSubdiv/issues/168#issuecomment-94041339","issue_url":"https://api.github.com/repos/PixarAnimationStudios/OpenSubdiv/issues/168","id":94041339,"user":{"login":"jcowles","id":1510114,"avatar_url":"https://avatars.githubusercontent.com/u/1510114?v=3","gravatar_id":"","url":"https://api.github.com/users/jcowles","html_url":"https://github.com/jcowles","followers_url":"https://api.github.com/users/jcowles/followers","following_url":"https://api.github.com/users/jcowles/following{/other_user}","gists_url":"https://api.github.com/users/jcowles/gists{/gist_id}","starred_url":"https://api.github.com/users/jcowles/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/jcowles/subscriptions","organizations_url":"https://api.github.com/users/jcowles/orgs","repos_url":"https://api.github.com/users/jcowles/repos","events_url":"https://api.github.com/users/jcowles/events{/privacy}","received_events_url":"https://api.github.com/users/jcowles/received_events","type":"User","site_admin":false},"created_at":"2015-04-17T18:06:33Z","updated_at":"2015-04-17T18:06:33Z","body":"To give an update, @takahito-tejima is still seeing this in the 3.0 codebase and had this to say:\r\n\r\n> This is likely a bug in gregory patch evaluation. It has to be C1 continuous, but we've seen one of the 4 edges of gregory patch show discontinuity and it ends up cracks when we apply displacement along normals.\r\n>\r\n> Yesterday I thought George's fix might fix this issue, but I still saw that, so there's a bug somewhere else. \r\n\r\nWe'll continue to track this down.\r\n"}}