{"id":18683,"date":"2009-03-30T10:00:00","date_gmt":"2009-03-30T10:00:00","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2009\/03\/30\/what-is-the-implementation-of-wm_printclient\/"},"modified":"2009-03-30T10:00:00","modified_gmt":"2009-03-30T10:00:00","slug":"what-is-the-implementation-of-wm_printclient","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20090330-00\/?p=18683","title":{"rendered":"What is the implementation of WM_PRINTCLIENT?"},"content":{"rendered":"

\nVia the suggestion box,\n\nMartin Filteau asks<\/A>\n<\/P>\n

\n

\nCould you explain the implementation of WM_PRINTCLIENT?\n<\/P>\n

\nIt seems that even MS got it wrong in the LISTBOX control.\n<\/P>\n

\nTry to AnimateWindow a window that as a LISTBOX control as a child.\nThe LISTBOX displays correctly if it is NOT empty.\nHowever, if it is empty… nothing is drawn.\n<\/P>\n

\nI got a similar problem when embedding an Internet Explorer control.\n<\/P>\n

\nThanks.\n<\/P>\n

\n-mf\n<\/P>\n<\/BLOCKQUOTE>\n

\nAs I noted back in 2003,\n\nthe implementation of WM_PRINTCLIENT<\/CODE> is the same as\nthat of WM_PAINT<\/CODE><\/A>.\nIn particular, the implementation of WM_PRINTCLIENT<\/CODE> for\nan empty window is… to paint nothing.\nThat’s why the window is empty.\n<\/P>\n

\nIn other words, the listbox control is correct to draw nothing when it\nis empty.\nTo draw the empty set, you draw nothing!\n<\/P>\n

\nLet’s make some changes to\n\nthe scratch program<\/A>\nto show that animating\na window with an empty listbox as a child works just fine.\n<\/P>\n

\nBOOL\nOnCreate(HWND hwnd, LPCREATESTRUCT lpcs)\n{\n    RECT rc;\n    GetClientRect(hwnd, &rc);\n    g_hwndChild = CreateWindow(\n        TEXT(“listbox”), NULL, WS_CHILD | WS_VISIBLE | WS_TABSTOP,\n        0, 0,\n       (rc.right – rc.left)\/2, rc.bottom – rc.top,\n       hwnd, (HMENU)1, g_hinst, 0);<\/FONT><\/p>\n
    return TRUE;\n}<\/p>\n
BOOL\nInitApp(void)\n{\n    …\n    wc.hbrBackground = (HBRUSH)(COLOR_APPWORKSPACE<\/FONT> + 1);\n    …\n}<\/p>\n
int WINAPI WinMain(HINSTANCE hinst, HINSTANCE hinstPrev,\n                   LPSTR lpCmdLine, int nShowCmd)\n{\n    …\n        \/\/ ShowWindow(hwnd, nShowCmd);<\/STRIKE>\n        AnimateWindow(hwnd, 2000, AW_VER_POSITIVE);<\/FONT>\n    …\n}\n<\/PRE>\n
\nJust to emphasize that the white background in the listbox is really\nbeing drawn by the listbox’s WM_ERASEBKGND<\/CODE> handler\nand isn’t just leftover pixels from its parent window,\nI’ve positioned the listbox so it covers only half of the parent\nwindow and set the parent window’s\nbackground to the application workspace color.\n(If your application workspace color is the same as\nthe window color, then set the parent background color to something else.\nI can’t believe I had to write that.)\n<\/P>\n
\nWith that simple set-up, we ask AnimateWindow<\/CODE> to show\nour window, and specify a custom animation time so it’s easier to\nsee that the color is correct throughout the entire animation.\nThe listbox child window does appear correctly:\nAll you get is the window background.\nNothing is drawn. just like it’s supposed to be.\n<\/P>\n
\n(This particular entry falls into another category of frustrating\ncomment: The comment that claims that something doesn’t work when it does,\nand forces me to write a test program to prove it.)\n<\/P><\/p>\n","protected":false},"excerpt":{"rendered":"
Via the suggestion box, Martin Filteau asks Could you explain the implementation of WM_PRINTCLIENT? It seems that even MS got it wrong in the LISTBOX control. Try to AnimateWindow a window that as a LISTBOX control as a child. The LISTBOX displays correctly if it is NOT empty. However, if it is empty… nothing is […]<\/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":[25],"class_list":["post-18683","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
Via the suggestion box, Martin Filteau asks Could you explain the implementation of WM_PRINTCLIENT? It seems that even MS got it wrong in the LISTBOX control. Try to AnimateWindow a window that as a LISTBOX control as a child. The LISTBOX displays correctly if it is NOT empty. However, if it is empty… nothing is […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/18683","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=18683"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/18683\/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=18683"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=18683"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=18683"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}