Create Device Context with Icon and transparent background-CodePudding

The

Even if I don't draw the icon, the output is a black square.

Can you suggest how to remove the background? In basic winapi calls. The code can be in cpp if it doesn't use special classes from libraries, I can use only dllCalls

Here is full working code:

// ignore_for_file: depend_on_referenced_packages, non_constant_identifier_names, avoid_print, unrelated_type_equality_checks import 'dart:ffi'; import 'dart:io'; import 'package:win32/win32.dart'; import 'package:ffi/ffi.dart'; int enumWindowsProc(int hWnd, int lparam) { if (IsWindowVisible(hWnd) == FALSE) return TRUE; final length = GetWindowTextLength(hWnd); if (length == 0) return TRUE; var icon = SendMessage(hWnd, WM_GETICON, 2, 0); // ICON_SMALL2 - User Made Apps if (icon == 0) icon = GetClassLongPtr(hWnd, -14); // GCLP_HICON - Microsoft Win Apps if (icon == 0) { icon = 0; return 1; } final int hScreen = GetDC(hWnd); final int hDC = CreateCompatibleDC(hScreen); final int hBitmap = CreateCompatibleBitmap(hScreen, GetSystemMetrics(SM_CXICON), GetSystemMetrics(SM_CYICON)); SelectObject(hDC, hBitmap); SetBkMode(hDC, TRANSPARENT); //- Works for text only PatBlt(hDC, 0, 0, GetSystemMetrics(SM_CXICON) ~/ 2, GetSystemMetrics(SM_CYICON), WHITENESS); // test, half white half black. DrawIconEx(hDC, 0, 0, icon, GetSystemMetrics(SM_CXICON), GetSystemMetrics(SM_CYICON), NULL, NULL, 3); //Turn to bytes final bmpScreen = calloc<BITMAP>(); GetObject(hBitmap, sizeOf<BITMAP>(), bmpScreen); final bitmapFileHeader = calloc<BITMAPFILEHEADER>(); final bitmapInfoHeader = calloc<BITMAPINFOHEADER>() ..ref.biSize = sizeOf<BITMAPINFOHEADER>() ..ref.biWidth = bmpScreen.ref.bmWidth ..ref.biHeight = bmpScreen.ref.bmHeight ..ref.biPlanes = 1 ..ref.biBitCount = 32 ..ref.biCompression = BI_RGB; final dwBmpSize = ((bmpScreen.ref.bmWidth * bitmapInfoHeader.ref.biBitCount 31) / 32 * 4 * bmpScreen.ref.bmHeight).toInt(); final lpBitmap = calloc<Uint8>(dwBmpSize); GetDIBits(hDC, hBitmap, 0, bmpScreen.ref.bmHeight, lpBitmap, bitmapInfoHeader.cast(), DIB_RGB_COLORS); final dwSizeOfDIB = dwBmpSize sizeOf<BITMAPFILEHEADER>() sizeOf<BITMAPINFOHEADER>(); bitmapFileHeader.ref.bfOffBits = sizeOf<BITMAPFILEHEADER>() sizeOf<BITMAPINFOHEADER>(); bitmapFileHeader.ref.bfSize = dwSizeOfDIB; bitmapFileHeader.ref.bfType = 0x4D42; // BM var b = BytesBuilder(); b.add(Pointer<Uint8>.fromAddress(bitmapFileHeader.address).asTypedList(sizeOf<BITMAPFILEHEADER>())); b.add(Pointer<Uint8>.fromAddress(bitmapInfoHeader.address).asTypedList(sizeOf<BITMAPINFOHEADER>())); b.add(lpBitmap.asTypedList(dwBmpSize)); // I need the Bitmap in Bytes, I save it to file just for debugging. //capture?.icon = b.takeBytes(); // DeleteDC(hDC); DeleteObject(hBitmap); free(bmpScreen); free(bitmapFileHeader); free(bitmapInfoHeader); free(lpBitmap); Directory current = Directory.current; File("${current.path}/imgs/i_${icon.toString()}.bmp").writeAsBytes(b.takeBytes()); return 1; } void main() { final imgs = "${Directory.current.path}/imgs"; if (Directory(imgs).exists() == true) { Directory(imgs).deleteSync(recursive: true); } final wndProc = Pointer.fromFunction<EnumWindowsProc>(enumWindowsProc, 0); EnumWindows(wndProc, 0); } final _user32 = DynamicLibrary.open('user32.dll'); int DrawIconEx(int hdc, int xLeft, int yTop, int hIcon, int cxWidth, int cyWidth, int istepIfAniCur, int hbrFlickerFreeDraw, int diFlags) => _DrawIconEx(hdc, xLeft, yTop, hIcon, cxWidth, cyWidth, istepIfAniCur, hbrFlickerFreeDraw, diFlags); final _DrawIconEx = _user32.lookupFunction< Int32 Function(IntPtr hdc, Int32 xLeft, Int32 yTop, IntPtr hIcon, Int32 cxWidth, Int32 cyWidth, Uint32 istepIfAniCur, IntPtr hbrFlickerFreeDraw, Uint32 diFlags), int Function(int hdc, int xLeft, int yTop, int hIcon, int cxWidth, int cyWidth, int istepIfAniCur, int hbrFlickerFreeDraw, int diFlags)>('DrawIconEx'); final _gdi32 = DynamicLibrary.open('gdi32.dll'); int PatBlt(int hdc, int x, int y, int w, int h, int rop) => _PatBlt(hdc, x, y, w, h, rop); final _PatBlt = _gdi32.lookupFunction<Int32 Function(IntPtr hdc, Int32 x, Int32 y, Int32 w, Int32 h, Uint32 rop), int Function(int hdc, int x, int y, int w, int h, int rop)>('PatBlt');

CodePudding user response：

Found a solution.

static BITMAP_AND_BYTES createAlphaChannelBitmapFromIcon(HICON hIcon) { // Get the icon info ICONINFO iconInfo = {0}; GetIconInfo(hIcon, &iconInfo); // Get the screen DC HDC dc = GetDC(NULL); // Get icon size info BITMAP bm = {0}; GetObject( iconInfo.hbmColor, sizeof( BITMAP ), &bm ); // Set up BITMAPINFO BITMAPINFO bmi = {0}; bmi.bmiHeader.biSize = sizeof(BITMAPINFOHEADER); bmi.bmiHeader.biWidth = bm.bmWidth; bmi.bmiHeader.biHeight = -bm.bmHeight; bmi.bmiHeader.biPlanes = 1; bmi.bmiHeader.biBitCount = 32; bmi.bmiHeader.biCompression = BI_RGB; // Extract the color bitmap int nBits = bm.bmWidth * bm.bmHeight; int32_t* colorBits = new int32_t[nBits]; GetDIBits(dc, iconInfo.hbmColor, 0, bm.bmHeight, colorBits, &bmi, DIB_RGB_COLORS); // Check whether the color bitmap has an alpha channel. // (On my Windows 7, all file icons I tried have an alpha channel.) BOOL hasAlpha = FALSE; for (int i = 0; i < nBits; i ) { if ((colorBits[i] & 0xff000000) != 0) { hasAlpha = TRUE; break; } } // If no alpha values available, apply the mask bitmap if (!hasAlpha) { // Extract the mask bitmap int32_t* maskBits = new int32_t[nBits]; GetDIBits(dc, iconInfo.hbmMask, 0, bm.bmHeight, maskBits, &bmi, DIB_RGB_COLORS); // Copy the mask alphas into the color bits for (int i = 0; i < nBits; i ) { if (maskBits[i] == 0) { colorBits[i] |= 0xff000000; } } delete[] maskBits; } // Release DC and GDI bitmaps ReleaseDC(NULL, dc); ::DeleteObject(iconInfo.hbmColor); ::DeleteObject(iconInfo.hbmMask); // Create GDI Bitmap Gdiplus::Bitmap* bmp = new Gdiplus::Bitmap(bm.bmWidth, bm.bmHeight, bm.bmWidth*4, PixelFormat32bppARGB, (BYTE*)colorBits); BITMAP_AND_BYTES ret = {bmp, colorBits}; return ret; }

Original post: https://stackoverflow.com/a/22885412/1456151

And also from PowerToys source code:

HBITMAP CreateBitmapFromIcon(_In_ HICON hIcon, _In_opt_ UINT width, _In_opt_ UINT height) { HBITMAP hBitmapResult = NULL; // Create compatible DC HDC hDC = CreateCompatibleDC(NULL); if (hDC != NULL) { // Get bitmap rectangle size RECT rc = { 0 }; rc.left = 0; rc.right = (width != 0) ? width : GetSystemMetrics(SM_CXSMICON); rc.top = 0; rc.bottom = (height != 0) ? height : GetSystemMetrics(SM_CYSMICON); // Create bitmap compatible with DC BITMAPINFO BitmapInfo; ZeroMemory(&BitmapInfo, sizeof(BITMAPINFO)); BitmapInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER); BitmapInfo.bmiHeader.biWidth = rc.right; BitmapInfo.bmiHeader.biHeight = rc.bottom; BitmapInfo.bmiHeader.biPlanes = 1; BitmapInfo.bmiHeader.biBitCount = 32; BitmapInfo.bmiHeader.biCompression = BI_RGB; HDC hDCBitmap = GetDC(NULL); HBITMAP hBitmap = CreateDIBSection(hDCBitmap, &BitmapInfo, DIB_RGB_COLORS, NULL, NULL, 0); ReleaseDC(NULL, hDCBitmap); if (hBitmap != NULL) { // Select bitmap into DC HBITMAP hBitmapOld = (HBITMAP)SelectObject(hDC, hBitmap); if (hBitmapOld != NULL) { // Draw icon into DC if (DrawIconEx(hDC, 0, 0, hIcon, rc.right, rc.bottom, 0, NULL, DI_NORMAL)) { // Restore original bitmap in DC hBitmapResult = (HBITMAP)SelectObject(hDC, hBitmapOld); hBitmapOld = NULL; hBitmap = NULL; } if (hBitmapOld != NULL) { SelectObject(hDC, hBitmapOld); } } if (hBitmap != NULL) { DeleteObject(hBitmap); } } DeleteDC(hDC); } return hBitmapResult; }