{"id":34733,"date":"2005-08-03T10:00:16","date_gmt":"2005-08-03T10:00:16","guid":{"rendered":"https:\/\/blogs.msdn.microsoft.com\/oldnewthing\/2005\/08\/03\/drawing-a-monochrome-bitmap-with-transparency\/"},"modified":"2005-08-03T10:00:16","modified_gmt":"2005-08-03T10:00:16","slug":"drawing-a-monochrome-bitmap-with-transparency","status":"publish","type":"post","link":"https:\/\/devblogs.microsoft.com\/oldnewthing\/20050803-16\/?p=34733","title":{"rendered":"Drawing a monochrome bitmap with transparency"},"content":{"rendered":"

\nLast time, I left you with a brief puzzle<\/A>.\nHere are two approaches.\nI am not a GDI expert, so there may be even better solutions\nout there.\nTo emphasize the transparency, I’ll change the window background\ncolor to the application workspace color.\n<\/P>\n

\n BOOL WinRegisterClass(WNDCLASS *pwc)\n {\n  pwc->hbrBackground = (HBRUSH)(COLOR_APPWORKSPACE<\/FONT> + 1);\n  return __super::WinRegisterClass(pwc);\n }\n<\/PRE>\n
\nMethod 1<\/STRONG>:\nA big\n\nMaskBlt<\/CODE><\/A>.\n<\/P>\n
\nvoid RootWindow::PaintContent(PAINTSTRUCT *pps)\n{\n HDC hdcMem = CreateCompatibleDC(pps->hdc);\n if (hdcMem) {\n  int cxCheck = GetSystemMetrics(SM_CXMENUCHECK);\n  int cyCheck = GetSystemMetrics(SM_CYMENUCHECK);\n  HBITMAP hbmMono = CreateBitmap(cxCheck, cyCheck, 1, 1, NULL);\n  if (hbmMono) {\n   HBITMAP hbmPrev = SelectBitmap(hdcMem, hbmMono);\n   if (hbmPrev) {\n    RECT rc = { 0, 0, cxCheck, cyCheck };\n    DrawFrameControl(hdcMem, &rc, DFC_MENU, DFCS_MENUCHECK);\n    COLORREF clrTextPrev = SetTextColor(pps->hdc,\n                                     GetSysColor(COLOR_MENUTEXT));\n    \/\/ COLORREF clrBkPrev = SetBkColor(pps->hdc,<\/STRIKE>\n    \/\/                                  GetSysColor(COLOR_MENU));<\/STRIKE>\n    MaskBlt(pps->hdc, 0, 0, cxCheck, cyCheck,\n           hdcMem, 0, 0, hbmMono, 0, 0\n           MAKEROP4(0x00AA0029, SRCCOPY));\n    \/\/ SetBkColor(pps->hdc, clrBkPrev);<\/STRIKE><\/FONT>\n    SetTextColor(pps->hdc, clrTextPrev);\n    SelectBitmap(hdcMem, hbmPrev);\n   }\n   DeleteObject(hbmMono);\n  }\n  DeleteDC(hdcMem);\n }\n}\n<\/PRE>\n
\nThis has the least amount of typing but feels like\noverkill to me, using a quaternary raster operation\nas if were a ternary, just because I didn’t want to create a\npattern brush.\n(The raster operation 0x00AA0029 is the NOP operator; it leaves\nthe destination alone.  I didn’t have this memorized;\nI looked it up\n\nin the documentation<\/a>.)\nThe MAKEROP4<\/CODE> says that for each white pixel in the mask,\ndo nothing (NOP), and for each black pixel, do a SRCCOPY<\/CODE>.\n<\/P>\n
\nNotice that the background color is never used\n(since it’s supposed to be transparent); consequently, we can delete\nthe code that sets and restores the DC’s background color.\n<\/P>\n
\nMethod 2<\/STRONG>:\nThe traditional two-step.\n<\/P>\n
\nvoid RootWindow::PaintContent(PAINTSTRUCT *pps)\n{\n HDC hdcMem = CreateCompatibleDC(pps->hdc);\n if (hdcMem) {\n  int cxCheck = GetSystemMetrics(SM_CXMENUCHECK);\n  int cyCheck = GetSystemMetrics(SM_CYMENUCHECK);\n  HBITMAP hbmMono = CreateBitmap(cxCheck, cyCheck, 1, 1, NULL);\n  if (hbmMono) {\n   HBITMAP hbmPrev = SelectBitmap(hdcMem, hbmMono);\n   if (hbmPrev) {\n    RECT rc = { 0, 0, cxCheck, cyCheck };\n    DrawFrameControl(hdcMem, &rc, DFC_MENU, DFCS_MENUCHECK);\n    COLORREF clrTextPrev = SetTextColor(pps->hdc, RGB(0,0,0)<\/FONT>);\n    COLORREF clrBkPrev = SetBkColor(pps->hdc, RGB(255,255,255)<\/FONT>);\n    BitBlt(pps->hdc, cxCheck, 0, cxCheck, cyCheck,\n           hdcMem, 0, 0, SRCAND);\n    SetTextColor(pps->hdc, GetSysColor(COLOR_MENUTEXT));\n    SetBkColor(pps->hdc, RGB(0,0,0));\n    BitBlt(pps->hdc, cxCheck, 0, cxCheck, cyCheck,\n           hdcMem, 0, 0, SRCPAINT);<\/FONT>\n    SetBkColor(pps->hdc, clrBkPrev);\n    SetTextColor(pps->hdc, clrTextPrev);\n    SelectBitmap(hdcMem, hbmPrev);\n   }\n   DeleteObject(hbmMono);\n  }\n  DeleteDC(hdcMem);\n }\n}\n<\/PRE>\n
\nThis is the traditional two-step blit.\nThe first erases the pixels that are about to be overwritten\nby setting the foreground to black and background to white,\nthen using SRCAND<\/CODE>.\nThis has the effect of erasing all the foreground pixels to zero\nwhile leaving the background intact.\nThe second blit does the same, but with SRCPAINT<\/CODE>.\nThis means that the background pixels need to be treated as black,\nso that when they are “or”d with the destination, the destination\npixels are unchanged.\nThe foreground pixels get the desired foreground color.\n<\/P>\n
\nThis method can be shortened by negating the first blit,\nreversing the sense of foreground and background, so that the\ncolor black doesn’t have to move between the background color\nand the text color.\n<\/P>\n
\nvoid RootWindow::PaintContent(PAINTSTRUCT *pps)\n{\n HDC hdcMem = CreateCompatibleDC(pps->hdc);\n if (hdcMem) {\n  int cxCheck = GetSystemMetrics(SM_CXMENUCHECK);\n  int cyCheck = GetSystemMetrics(SM_CYMENUCHECK);\n  HBITMAP hbmMono = CreateBitmap(cxCheck, cyCheck, 1, 1, NULL);\n  if (hbmMono) {\n   HBITMAP hbmPrev = SelectBitmap(hdcMem, hbmMono);\n   if (hbmPrev) {\n    RECT rc = { 0, 0, cxCheck, cyCheck };\n    DrawFrameControl(hdcMem, &rc, DFC_MENU, DFCS_MENUCHECK);\n    COLORREF clrTextPrev = SetTextColor(pps->hdc, RGB(255,255,255)<\/FONT>);\n    COLORREF clrBkPrev = SetBkColor(pps->hdc, RGB(0,0,0)<\/FONT>);\n    BitBlt(pps->hdc, cxCheck, 0, cxCheck, cyCheck,\n           hdcMem, 0, 0, 0x00220326); \/\/ DSna\n    SetTextColor(pps->hdc, GetSysColor(COLOR_MENUTEXT));\n    BitBlt(pps->hdc, cxCheck, 0, cxCheck, cyCheck,\n           hdcMem, 0, 0, SRCPAINT);<\/FONT>\n    SetBkColor(pps->hdc, clrBkPrev);\n    SetTextColor(pps->hdc, clrTextPrev);\n    SelectBitmap(hdcMem, hbmPrev);\n   }\n   DeleteObject(hbmMono);\n  }\n  DeleteDC(hdcMem);\n }\n}\n<\/PRE>\n
\nWhether this shortening is actually an overall\nimprovement is difficult to tell.\nIt’s possible that some display drivers have a highly optimized\nSRCAND<\/CODE> handler whereas they are less likely to have\nan optimized 0x00220326<\/CODE> handler.\n<\/P>\n
\n(Exercise: Why can’t you instead reverse the second blit,\nconverting it to a MERGEPAINT<\/CODE>?)\n<\/P><\/p>\n","protected":false},"excerpt":{"rendered":"
Last time, I left you with a brief puzzle. Here are two approaches. I am not a GDI expert, so there may be even better solutions out there. To emphasize the transparency, I’ll change the window background color to the application workspace color. BOOL WinRegisterClass(WNDCLASS *pwc) { pwc->hbrBackground = (HBRUSH)(COLOR_APPWORKSPACE + 1); return __super::WinRegisterClass(pwc); } […]<\/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-34733","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-oldnewthing","tag-code"],"acf":[],"blog_post_summary":"
Last time, I left you with a brief puzzle. Here are two approaches. I am not a GDI expert, so there may be even better solutions out there. To emphasize the transparency, I’ll change the window background color to the application workspace color. BOOL WinRegisterClass(WNDCLASS *pwc) { pwc->hbrBackground = (HBRUSH)(COLOR_APPWORKSPACE + 1); return __super::WinRegisterClass(pwc); } […]<\/p>\n","_links":{"self":[{"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/34733","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=34733"}],"version-history":[{"count":0,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/posts\/34733\/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=34733"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/categories?post=34733"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/devblogs.microsoft.com\/oldnewthing\/wp-json\/wp\/v2\/tags?post=34733"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}