{"id":40663,"date":"2004-02-11T07:00:00","date_gmt":"2004-02-11T07:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2004\/02\/11\/sure-we-do-that\/"},"modified":"2004-02-11T07:00:00","modified_gmt":"2004-02-11T07:00:00","slug":"sure-we-do-that","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20040211-00\/?p=40663","title":{"rendered":"Sure, we do that"},"content":{"rendered":"

The DirectX video driver interface for Windows 95\nhad a method that each driver exposed called something\nlike “DoesDriverSupport(REFGUID guidCapability)” where we\nhanded it a capability GUID and it said whether or not\nthat feature was supported.<\/p>\n

\nThere were various capability GUIDs defined, things like\nGUID_CanStretchAlpha to ask the driver whether it was\ncapable of stretching a bitmap with an alpha channel.\n<\/p>\n

\nThere was one driver that returned TRUE when you called\nDoesDriverSupport(GUID_XYZ), but when DirectDraw\ntried to use that capability, it failed, and in a pretty\nspectacular manner.\n<\/p>\n

\nSo one of the DirectDraw developers called the vendor and\nasked them, “So does your card do XYZ?”\n<\/p>\n

\nTheir response: “What’s XYZ?”\n<\/p>\n

\nTurns out that their driver’s implementation of DoesDriverSupport\nwas something like this:\n<\/p>\n

\nBOOL DoesDriverSupport(REFGUID guidCapability)\n{\n  return TRUE;\n}\n<\/pre>\n
\nIn other words, whenever DirectX asked, “Can you do this?”\nthey answered, “Sure, we do that,” without even checking what\nthe question was.\n<\/p>\n
\n(The driver must have been written by the sales department.)\n<\/p>\n
\nSo the DirectDraw folks changed the way they queried for\ndriver capabilities.  One of the developers went into his\nboss’s office, took a network card, extracted the\n\nMAC address<\/a>, and then smashed the card with a hammer.\n<\/p>\n
\nYou see, this last step was important: The GUID generation\nalgorithm is based on a combination of time and space.\nWhen you ask CoCreateGuid to create a new GUID, it encodes\nthe time of your request in the first part of the GUID\nand information that uniquely identifies your machine\n(the network card’s MAC address, which is required\nto be unique by the standards that apply to network card).\n<\/p>\n
\nBy smashing the network card with a hammer, he prevented\nthat network card from ever being used to generate a GUID.\n<\/p>\n
Next, he added code to DirectDraw so that when it starts up,\nit manufactures a random GUID based on that network card\n(which – by its having been destroyed – can never be validly created)\nand passes it to DoesDriverSupport.\nIf the driver says, “Sure, we do that”, DirectDraw says,\n“Aha! Caught you! I will not believe anything you say from now on.”<\/p>\n","protected":false},"excerpt":{"rendered":"
The DirectX video driver interface for Windows 95 had a method that each driver exposed called something like “DoesDriverSupport(REFGUID guidCapability)” where we handed it a capability GUID and it said whether or not that feature was supported. There were various capability GUIDs defined, things like GUID_CanStretchAlpha to ask the driver whether it was capable of stretching […]<\/p>\n","protected":false},"author":1069,"featured_media":111744,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[1],"tags":[2],"class_list":["post-40663","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-history"],"acf":[],"blog_post_summary":"
The DirectX video driver interface for Windows 95 had a method that each driver exposed called something like “DoesDriverSupport(REFGUID guidCapability)” where we handed it a capability GUID and it said whether or not that feature was supported. There were various capability GUIDs defined, things like GUID_CanStretchAlpha to ask the driver whether it was capable of stretching […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/40663","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/users\/1069"}],"replies":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/comments?post=40663"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/40663\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media\/111744"}],"wp:attachment":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/media?parent=40663"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=40663"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=40663"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}