\nOnce you make it possible to do something,\nyou have to accept that you also made it possible to do something wrong<\/i>.\n<\/p>\n
\nWhen the window manager was originally designed,\nit made it possible for programs to override many standard behaviors.\nThey could handle the \nThe downside is that it also permits stupid people to do dumb things.\n<\/p>\n \n\nChanging the window procedure model from\ncall \nDoing a little bit<\/i> is a very common pattern.\nThe \nHow would you do this with the handled\/not-handled model?\n<\/p>\n \nThe trick about that bit in parentheses is that it requires\nthe research department to finish the final details on that\ntime machine they’ve been working on.\nIt’s basically saying, “Return not handled<\/i>,\nthen follow the message until handling is complete\nand if the final result is \nAnd even if the research department comes through with that\ntime machine,\nthe handled\/not-handled model doesn’t even solve the original problem!\n<\/p>\n \nThe original problem was people failing to call\n \n(Side note: The dialog manager uses the handled\/not-handled model,\nand\n\nsome people would prefer that it use the\n \nThis topic raises another one of those “No matter what you do,\nsomebody will call you an idiot” dilemmas.\nOn the one side, there’s the\n\nWindows should perform extra testing at runtime to\ndetect bad applications<\/i><\/a> school,\nand on the other side, there’s the\n\nWindows should get rid of all the code whose sole purpose\nin life is to detect bad applications<\/i><\/a> school.<\/p>\n","protected":false},"excerpt":{"rendered":" Once you make it possible to do something, you have to accept that you also made it possible to do something wrong. When the window manager was originally designed, it made it possible for programs to override many standard behaviors. They could handle the WM_NCHITTEST message so a window can be dragged by grabbing any […]<\/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":[26],"class_list":["post-10593","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-other"],"acf":[],"blog_post_summary":" Once you make it possible to do something, you have to accept that you also made it possible to do something wrong. When the window manager was originally designed, it made it possible for programs to override many standard behaviors. They could handle the WM_NCHITTEST message so a window can be dragged by grabbing any […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/10593","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=10593"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/10593\/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=10593"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=10593"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=10593"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}WM_NCHITTEST<\/code> message\n\nso a window can be dragged by grabbing any part of the window,\nnot just the caption bar<\/a>.\nThey could handle the WM_NCPAINT<\/code> message\nto draw custom title bars.\nThe theory was that making all of these things possible\npermitted smart people to do clever things.\n<\/p>\nDefWindowProc<\/code> to get default behavior<\/i>\nto\nreturn whether you handled the message<\/i><\/a>\nwouldn’t have helped.\nFirst of all, the handled\/not-handled model is too restrictive:\nIt requires you to do everything<\/i> (handled)\nor nothing<\/i> (not handled).\nThere is no option to do a little bit<\/i>.\n(Imagine if C++ didn’t let you call the base class implementation\nof an overridden method.)\n<\/p>\nWM_NCHITTEST<\/code> technique mentioned above,\nfor example, uses the default hit-testing implementation,\nand then tweaks the result slightly:\n<\/p>\n\ncase WM_NCHITTEST:\n \/\/ call base class first\n lres = DefWindowProc(hwnd, uMsg, wParam, lParam);\n \/\/ tweak the result\n if (lres == HTCLIENT) lres = HTCAPTION;\n return lres;\n<\/pre>\n
\ncase WM_NCHITTEST:\n if (not handling this message would have resulted in HTCLIENT) {\n lres = HTCAPTION;\n handled = TRUE;\n } else {\n handled = FALSE;\n }\n break;\n<\/pre>\nHTCLIENT<\/code>,\nthen fire up the time machine and rewind to this point\nso I can change my mind and return handled<\/i> instead.”\n<\/p>\nDefWindowProc<\/code>\nwhen they decided that they didn’t want to handle a message.\nIn the handled\/not-handled model, the equivalent problem would be\npeople returning handled = TRUE<\/code> unconditionally.\n<\/p>\n\nBOOL NewStyleWindowProc(HWND hwnd, UINT uMsg,\n WPARAM wParam, LPARAM lParam, LRESULT& lres)\n{\n BOOL handled = TRUE;\n switch (uMsg) {\n case WM_THIS: ...; break;\n case WM_THAT: ...; break;\n \/\/ no \"default: handled = FALSE; break;\"\n }\n return handled;\n}\n<\/pre>\nDefXxxProc<\/code> model<\/a>,\nso you might say “We tried that, and some people didn’t like it.”)\n<\/p>\n