I am no expert in anything GDI. But I was given some code YEARS ago which has served me decently well. But, it's getting old ... and with new windows10 dark theme, it's showing it's flaws.
I am rendering a menu (in an explorer menu plugin). Here's the snippet of code used to generate the bitmap.
My goal, to convert this code to generate a bitmap with transparency of the icon preserved.
(the result HBITMAP ends up in pItem->m_hBitmap )
HICON hIcon;
if ( (iIndex >= 0) && (ExtractIconEx(iconDLLPath, iIndex, NULL, &hIcon, 1) != 0) )
{
HDC hdc = CreateIC(L"DISPLAY", NULL, NULL, NULL);
HDC hdcMem = CreateCompatibleDC(hdc);
// XP demands 12x12, otherwise use 16x16
int cx = GetSystemMetrics((m_bUseSmallerIcons) ? SM_CXMENUCHECK : SM_CXSMICON);
int cy = GetSystemMetrics((m_bUseSmallerIcons) ? SM_CYMENUCHECK : SM_CYSMICON);
pItem->m_hBitmap = CreateCompatibleBitmap(hdc, cx, cy);
HBITMAP hBmOld = (HBITMAP) SelectObject(hdcMem, pItem->m_hBitmap);
// DC: paint entire mem dc COLOR_MENU so icon looks transparent
// when painted into context menu having this background color
HBRUSH hBrush = CreateSolidBrush(GetSysColor(COLOR_MENU));
RECT rect;
rect.left = 0;
rect.top = 0;
rect.right = cx;
rect.bottom = cy;
FillRect(hdcMem, &rect, hBrush);
DeleteObject(hBrush);
// Draw icon transparently, on top of the background color. Transparent
// areas will be the background color.
DrawIconEx(hdcMem, 0, 0, hIcon, cx, cy, 0, 0, DI_NORMAL);
// Cleanup
SelectObject(hdcMem, hBmOld);
DeleteDC(hdc);
DeleteDC(hdcMem);
DestroyIcon(hIcon);
}
I should remove the which draws the white background, but how do I put down a transparent background? Everything I've tried yields a black background.
* just removing the white "fill"
* SetBkMode(TRANSPARENT)
* using the theme code to get the menu color...
How do I go about making a proper bitmap with transparency?
Ultimately, the answer is that I am doing nothing wrong. This menu is rendered as part of a menu constructed in a shell plugin using IContextMenu.
The answer - implement IContextMenu2. And in doing so, do an owner draw menu item.
Related
As the title says I'm unable to FillRect bitmap to be transparent. I know when creating the bitmap it is not monochrome as gray brush works fine but I have no way (that I'm aware of) to check if it is colored or grayscale. I also am aware that by default the bitmap is black hence why I'm trying to change it to transparent. I am also aware that I'm likely not cleaning up the dc's correctly however that is not the main issue. I'm trying to solve the black background by making it transparent.
#include<windows.h>
#include<iostream>
int main()
{
// Init DC
HWND Wnd = GetDesktopWindow();//GetConsoleWindow();
HDC ScreenDC = GetDC(Wnd);
// Init Rectangle
RECT ClientRect;
GetClientRect(Wnd, &ClientRect);
// Init Double Buffer
HDC MemDC = CreateCompatibleDC(ScreenDC);
HBITMAP MemBM = CreateCompatibleBitmap(ScreenDC, ClientRect.right - ClientRect.left, ClientRect.bottom - ClientRect.top);
HBITMAP OldBM = (HBITMAP)SelectObject(MemDC, MemBM);
// Create Brush and Pen
HPEN Pen = CreatePen(PS_SOLID, 1, RGB(255, 0, 0));
HBRUSH ClearBrush = (HBRUSH)GetStockObject(GRAY_BRUSH);
// Set Brush and Pen
SelectObject(MemDC, Pen);
SelectObject(MemDC, ClearBrush);
POINT p;
while(!GetAsyncKeyState(VK_RETURN))
{
// Clear and Draw
GetCursorPos(&p);
FillRect(MemDC, &ClientRect, ClearBrush);
Rectangle(MemDC, p.x, p.y, p.x+20, p.y+20);
BitBlt(ScreenDC, 0, 0, ClientRect.right - ClientRect.left, ClientRect.bottom + ClientRect.left, MemDC, 0, 0, SRCCOPY);
}
SelectObject(MemDC, OldBM);
DeleteObject(ClearBrush);
DeleteObject(Pen);
DeleteObject(OldBM);
DeleteObject(MemBM);
DeleteDC(MemDC);
ReleaseDC(Wnd, ScreenDC);
return 0;
}
I've tried many different ways of setting transparent background to no avail. The end result is a rectangle appearing over the mouse and following it across the screen however the background shouldn't be black I should be able to see other windows.
I'm creating a new-UI walkthrough for my MFC application and want to highlight certain controls as the walkthrough proceeds. Specifically, I want to darken the whole window except the control I'm emphasizing.
I tried creating a partly-transparent black overlay using SetLayeredWindowAttributes, but this doesn't let me set a sub-area completely transparent. UpdateLayeredWindow can do this, but I'm not eager to create a BMP/PNG file for every control I need to highlight.
Can I create the transparency geometry dynamically? For example, can I draw bitmap transparency from scratch then load it into UpdateLayeredWindow?
I also need to be compatible with Windows 7 (despite its support EOL).
Follow-up:
Trying to paint transparent GDI+ regions, but doesn't work:
void ApplicationDlg::Highlight(const CRect& rect)
{
CRect wndRect;
GetWindowRect(&wndRect);
Gdiplus::Rect wndRectPlus(wndRect.left, wndRect.top, wndRect.Width(), wndRect.Height());
Gdiplus::Region wndRegion(wndRectPlus);
Gdiplus::Rect controlRectPlus(rect.left, rect.top, rect.Width(), rect.Height());
Gdiplus::Region highlightRegion(controlRectPlus);
wndRegion.Exclude(&highlightRegion);
Gdiplus::SolidBrush transparentBrush(Gdiplus::Color(0, 0, 0, 0));
Gdiplus::SolidBrush darkenBrush(Gdiplus::Color(128, 0, 0, 0));
CDC* pDCScreen = m_WalkthroughDlg.GetDC();
HDC hDC = CreateCompatibleDC(pDCScreen->m_hDC);
HBITMAP hBmp = CreateCompatibleBitmap(hDC, wndRect.Width(), wndRect.Height());
HBITMAP hBmpOld = (HBITMAP)SelectObject(hDC, hBmp);
Gdiplus::Graphics graphics(hDC);
graphics.FillRegion(&darkenBrush, &wndRegion);
graphics.FillRegion(&transparentBrush, &highlightRegion);
BLENDFUNCTION blend = {0};
blend.BlendOp = AC_SRC_OVER;
blend.SourceConstantAlpha = 255;
blend.AlphaFormat = AC_SRC_ALPHA;
SIZE sizeWnd = {wndRect.Width(), wndRect.Height()};
POINT ptSrc = {0,0};
m_WalkthroughDlg.UpdateLayeredWindow(pDCScreen, NULL, &sizeWnd, CDC::FromHandle(hDC), &ptSrc, NULL, &blend, ULW_ALPHA); // TODO cleanup FromHandle refs
m_WalkthroughDlg.BringWindowToTop();
SelectObject(hDC, hBmpOld);
DeleteObject(hBmp);
DeleteDC(hDC);
}
You can dynamically create a mask by using CRgn class: https://learn.microsoft.com/en-us/cpp/mfc/reference/crgn-class?view=vs-2019
It allows you to combine regions (if you need to highlight more than one area). You could then use FillRgn function to update the hdcSrc DC used in UpdateLayeredWindow.
Alternatively, if your highlights are rectangular, you could just draw rectangles on that hdcSrc.
I have a little modified QScreen::grabWindow function. And on some computers, unfortunately I didn't find relationship between them, BitBlt freezes for even minutes! Why this can happen and what can I do?
QPixmap DetectionFlow::grabScreen(HWND h)
{
RECT rect;
GetClientRect(h, (LPRECT)&rect);
// get the height and width of the screen
int height = rect.bottom - rect.top;
int width = rect.right - rect.left;
// Create and setup bitmap
HDC display_dc = GetDC(0);
HDC bitmap_dc = CreateCompatibleDC(display_dc);
HBITMAP bitmap = CreateCompatibleBitmap(display_dc, width, height);
HGDIOBJ null_bitmap = SelectObject(bitmap_dc, bitmap);
HDC window_dc = GetDC(h);
BitBlt(bitmap_dc, 0, 0, width, height, window_dc, 0, 0, SRCCOPY);
// clean up all but bitmap
ReleaseDC(h, window_dc);
SelectObject(bitmap_dc, null_bitmap);
DeleteDC(bitmap_dc);
const QPixmap pixmap = qt_pixmapFromWinHBITMAP(bitmap);
DeleteObject(bitmap);
ReleaseDC(0, display_dc);
return pixmap;
}
PS. What is interesting, on computers, where freezes, it freezes randomly. So usually there it works fast (a couple of ms) and then freeze.
Problem was in Aero. Computers that freezes with BitBlt has Win7 and Aero. Without Aero all ok.
Now I am working on a legacy product which use GDI to draw text in screen. Now I try to use DirectWrite to draw text for better appearance and accurancy of font. I am very curious that has anyone done this before?
I meet a problem that when I use DirectWrite to draw text on a GDI hdc, the background color is always white, I need a transparent background, is it possible? it seems that the SetBkMode is useless
The sample code is as below,
SetBkMode(hdc, TRANSPARENT); //hDC is the target GDI dc
SIZE size = {};
HDC memoryHdc = NULL;
memoryHdc = g_pBitmapRenderTarget->GetMemoryDC();
SetBkMode(memoryHdc, TRANSPARENT);
hr = g_pBitmapRenderTarget->GetSize(&size);
Rectangle(memoryHdc, 0, 0, size1.cx , size1.cy );
if (SUCCEEDED(hr)) {
hr = g_pTextLayout->Draw(NULL, g_pGdiTextRenderer, 0, 0);
}
BitBlt(hdc, x, y, width + 1, height + 1, memoryHdc, 0, 0, SRCCOPY | NOMIRRORBITMAP);
Default (Stock) brush for freshly created GDI device context is white solid brush, which is why you have white rectangle in output. See GetStockObject
GDI doesn't work with transparent images, BitBlt will replace all pixels inside destination rectangle in target DC. You have to copy contents of target DC destination rectangle in memory DC, then draw text and copy result back to achieve desired effect.
SetBkMode(hdc, TRANSPARENT); //hDC is the target GDI dc
SIZE size = {};
HDC memoryHdc = g_pBitmapRenderTarget->GetMemoryDC();
BitBlt(memoryHdc, 0, 0, width+1, height+1, hdc, x, y, SRCCOPY);
if (SUCCEEDED(hr)) {
hr = g_pTextLayout->Draw(NULL, g_pGdiTextRenderer, 0, 0);
}
BitBlt(hdc, x, y, width + 1, height + 1, memoryHdc, 0, 0, SRCCOPY | NOMIRRORBITMAP);
Make sure you use smallest possible update region, since moving large chunks of bitmaps in memory will surely dwindle performance.
If application uses back buffer to draw windows, memory DC of IDWriteBitmapRenderTarget could be used instead of allocating another one - in that case you solve problem of transparent text background automatically.
I am trying to draw a simple few rectangles and store the result, I only need to draw it once. So, keeping the HDC (hdcBackround) at the top "globaly."
void drawBackground(HWND hwnd) { // hwnd is the main windows handle
// dimensions
RECT rect;
GetWindowRect(hwnd, &rect);
HDC hWinDC = GetDC(hwnd);
hdcBackground = ::CreateCompatibleDC(hWinDC); // "global"
HBITMAP hbm = ::CreateCompatibleBitmap(hWinDC, rect.right, rect.bottom);
::SelectObject(hdcBackground, hbm);
SetBkMode(hdcBackground, TRANSPARENT);
SelectObject(hdcBackground, hFont[HF_DEFAULT]);
SelectObject(hdcBackground, hBrush[HB_TOPBG]);
SelectObject(hdcBackground, hPen[HP_THINBORDER]);
// draw
Rectangle(hdcBackground, 0, 0, rect.right, 20);
SelectObject(hdcBackground, hBrush[HB_LOWBG]);
Rectangle(hdcBackground, 50, 20, rect.right, 40);
// ??? clean up after it works
ReleaseDC(hwnd, hWinDC);
}
I call that function once, and in a timer I BitBlt() hdcBackground to the screens HDC. When I test it out, it draws both the rectangles, with a 1px border (as the pen is set as,) but there is no color, it is just black and white.
The brushes and such are all fine, it is just that I am not getting color. The RGB on the brushes are (25,25,25) and (65,65,65), dark grey.
Any ideas?
Thanks.