{"action":"created","issue":{"url":"https://api.github.com/repos/servo/webrender/issues/3122","repository_url":"https://api.github.com/repos/servo/webrender","labels_url":"https://api.github.com/repos/servo/webrender/issues/3122/labels{/name}","comments_url":"https://api.github.com/repos/servo/webrender/issues/3122/comments","events_url":"https://api.github.com/repos/servo/webrender/issues/3122/events","html_url":"https://github.com/servo/webrender/pull/3122","id":363783329,"node_id":"MDExOlB1bGxSZXF1ZXN0MjE4MTMyNzQ0","number":3122,"title":"Use the texture filtering hardware to reduce the number of sample operations in the blur shader.","user":{"login":"pcwalton","id":157897,"node_id":"MDQ6VXNlcjE1Nzg5Nw==","avatar_url":"https://avatars0.githubusercontent.com/u/157897?v=4","gravatar_id":"","url":"https://api.github.com/users/pcwalton","html_url":"https://github.com/pcwalton","followers_url":"https://api.github.com/users/pcwalton/followers","following_url":"https://api.github.com/users/pcwalton/following{/other_user}","gists_url":"https://api.github.com/users/pcwalton/gists{/gist_id}","starred_url":"https://api.github.com/users/pcwalton/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/pcwalton/subscriptions","organizations_url":"https://api.github.com/users/pcwalton/orgs","repos_url":"https://api.github.com/users/pcwalton/repos","events_url":"https://api.github.com/users/pcwalton/events{/privacy}","received_events_url":"https://api.github.com/users/pcwalton/received_events","type":"User","site_admin":false},"labels":[],"state":"open","locked":false,"assignee":null,"assignees":[],"milestone":null,"comments":9,"created_at":"2018-09-25T22:01:26Z","updated_at":"2018-10-30T02:29:54Z","closed_at":null,"author_association":"COLLABORATOR","pull_request":{"url":"https://api.github.com/repos/servo/webrender/pulls/3122","html_url":"https://github.com/servo/webrender/pull/3122","diff_url":"https://github.com/servo/webrender/pull/3122.diff","patch_url":"https://github.com/servo/webrender/pull/3122.patch"},"body":"Linear filtering allows us to evaluate the formula\r\n\r\n    k₀c₀ + k₁c₁                 (Equation 1)\r\n\r\nwhere c₀ and c₁ are the colors of adjacent texels and k₀ and k₁ are arbitrary\r\nfactors (in this case, the results of evaluating the Gaussian function) with a\r\nsingle lookup. Linear filtering evaluates the following expression for some t\r\nbetween 0 and 1:\r\n\r\n    lerp(c₀, c₁, t)\r\n\r\nIt can be shown algebraically that Equation 1 is equivalent to:\r\n\r\n                 ⎛           k₁  ⎞\r\n    (k₀ + k₁)lerp⎜c₀, c₁, ───────⎟\r\n                 ⎝        k₀ + k₁⎠\r\n\r\nWhich can be readily evaluated by letting `t = k₁/(k₀ + k₁)` and performing a\r\ntexture lookup.\r\n\r\nThis results in some minor visual differences because we always compute an even\r\nnumber of pixels on each side (i.e. the *support* is now always rounded up to\r\nthe nearest even number of pixels), whereas before we might have evaluated an\r\nodd number of pixels. All differences should therefore be minor quality\r\nimprovements.\r\n\r\nDon't merge this yet; I want to run tests and a try build.\n\n<!-- Reviewable:start -->\n---\nThis change is [<img src=\"https://reviewable.io/review_button.svg\" height=\"34\" align=\"absmiddle\" alt=\"Reviewable\"/>](https://reviewable.io/reviews/servo/webrender/3122)\n<!-- Reviewable:end -->\n"},"comment":{"url":"https://api.github.com/repos/servo/webrender/issues/comments/434149319","html_url":"https://github.com/servo/webrender/pull/3122#issuecomment-434149319","issue_url":"https://api.github.com/repos/servo/webrender/issues/3122","id":434149319,"node_id":"MDEyOklzc3VlQ29tbWVudDQzNDE0OTMxOQ==","user":{"login":"pcwalton","id":157897,"node_id":"MDQ6VXNlcjE1Nzg5Nw==","avatar_url":"https://avatars0.githubusercontent.com/u/157897?v=4","gravatar_id":"","url":"https://api.github.com/users/pcwalton","html_url":"https://github.com/pcwalton","followers_url":"https://api.github.com/users/pcwalton/followers","following_url":"https://api.github.com/users/pcwalton/following{/other_user}","gists_url":"https://api.github.com/users/pcwalton/gists{/gist_id}","starred_url":"https://api.github.com/users/pcwalton/starred{/owner}{/repo}","subscriptions_url":"https://api.github.com/users/pcwalton/subscriptions","organizations_url":"https://api.github.com/users/pcwalton/orgs","repos_url":"https://api.github.com/users/pcwalton/repos","events_url":"https://api.github.com/users/pcwalton/events{/privacy}","received_events_url":"https://api.github.com/users/pcwalton/received_events","type":"User","site_admin":false},"created_at":"2018-10-30T02:29:54Z","updated_at":"2018-10-30T02:29:54Z","author_association":"COLLABORATOR","body":"It was ready to go but I wasn't sure about try results. Let me try again."}}
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