I have a remote application that the a screenshot using "windows handle". ( I mean HDC, HBITMAP, ....).
The code look like this :
int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
HDC hDesktopDC = CreateDC(TEXT("DISPLAY"),NULL,NULL,NULL);
HDC hCaptureDC = CreateCompatibleDC(hDesktopDC);
HBITMAP hCaptureBitmap =CreateCompatibleBitmap(
hDesktopDC,
nScreenWidth,
nScreenHeight);
SelectObject(hCaptureDC,hCaptureBitmap);
BitBlt(
hCaptureDC,
0,0,
nScreenWidth,nScreenHeight,
hDesktopDC,
0,0,
SRCCOPY);
BITMAPINFOHEADER info;
info.biSize = sizeof(BITMAPINFOHEADER);
info.biWidth = nScreenWidth;
info.biHeight = nScreenHeight;
info.biPlanes = 1;
info.biBitCount = 32;
info.biCompression = BI_RGB;
info.biSizeImage = 0;
info.biXPelsPerMeter = 0;
info.biYPelsPerMeter = 0;
info.biClrUsed = 0;
info.biClrImportant = 0;
//reteive the image data
byte *bits= (byte*)malloc(nScreenWidth*nScreenHeight*4);
GetDIBits(hDesktopDC, // handle to DC
hCaptureBitmap, // handle to bitmap
0, // first scan line to set
nScreenHeight, // number of scan lines to copy
bits, // array for bitmap bits
(BITMAPINFO*)&info, // bitmap data buffer
DIB_RGB_COLORS // RGB
);
DeleteDC(hDesktopDC);
DeleteDC(hCaptureDC);
DeleteObject(hCaptureBitmap);
After many loop the (about 2000) the CreateDC() function return NULL. And, if I old the DC (mean intialize it once, then destroyed on application exit) my application window flick (or part of it) or even get entirely invisible.
Thus, I'll need to know how to figure this issue out or know any other better way to get the screen image (bits/RGB data).
Related
I currently am trying to take a screenshot of the screen, and then get it into a format editable by OpenCV. The code I'm using is from the microsoft website, https://learn.microsoft.com/en-gb/windows/win32/gdi/capturing-an-image. The code uses the "Windows.h" library. The easiest way of doing it is obviously to just save the bitmap as a .bmp, then open it using opencv. However, I would like it to be more efficient than that, and I don't know how to. When I used the code, it outputted a char pointer, which I don't know how to convert to a cv::Mat. The code is below:
cv::Mat * Capture::GetMat()
{
cv::Mat * mat1;
MemoryHandle = NULL;
BitmapHandle = NULL;
// Find the handle for the device context of the entire screen, and the specific window specified.
ScreenHandle = GetDC(NULL);
WindowHandle = GetDC(hwnd);
//Make the compatible DC (Device Context) for storing the data in memory.
MemoryHandle = CreateCompatibleDC(WindowHandle);
//Make a compatible DC for the bitmap to be stored in.
BitmapHandle = CreateCompatibleBitmap(WindowHandle, width, height);
//Select the correct bitmap, and put it into memory using the memory handle.
SelectObject(MemoryHandle, BitmapHandle);
//Transfer the actual bitmap into the compatible memory DC.
BitBlt(MemoryHandle, 0, 0, 1920, 1080, WindowHandle, 0, 0, SRCCOPY);
//Get the bitmap from the handle, and ready it to be filed.
GetObject(BitmapHandle, sizeof(BITMAP), &Bitmap);
//Cofinguring INFO details.
bmpInfoHeader.biSize = sizeof(BITMAPINFOHEADER);
bmpInfoHeader.biWidth = Bitmap.bmWidth;
bmpInfoHeader.biHeight = Bitmap.bmHeight;
bmpInfoHeader.biPlanes = 1;
bmpInfoHeader.biBitCount = 32;
bmpInfoHeader.biCompression = BI_RGB;
bmpInfoHeader.biSizeImage = 0;
bmpInfoHeader.biXPelsPerMeter = 0;
bmpInfoHeader.biYPelsPerMeter = 0;
bmpInfoHeader.biClrUsed = 0;
bmpInfoHeader.biClrImportant = 0;
bmpSize = ((Bitmap.bmWidth * bmpInfoHeader.biBitCount + 31) / 32) * 4 * Bitmap.bmHeight;
memhnd = GlobalAlloc(GHND, bmpSize);
mat1 = (cv::Mat *)GlobalLock(memhnd);
std::cout << GetLastError() << std::endl;
return mat1;
}
int Capture::save_mat(cv::Mat * mat)
{
std::string FileName("P:/Photos/capture");
FileName += std::to_string(image_count_mat);
FileName += (const char*)(".jpg");
cv::Mat mat2 = *mat;
cv::imwrite(FileName.c_str(), mat2);
image_count_mat++;
return 0;
}
The class has these attributes:
private:
HWND hwnd;
HDC hdc;
int image_count_bitmap = 0;
int image_count_mat = 0;
int height;
int width;
HDC ScreenHandle;
HDC WindowHandle;
HDC MemoryHandle = NULL;
HBITMAP BitmapHandle = NULL;
BITMAP Bitmap;
BITMAPFILEHEADER bmpFileHeader;
BITMAPINFOHEADER bmpInfoHeader;
DWORD bmpSize;
HANDLE memhnd;
The GetMat() function works fine and doesn't output an error, although I have no idea how to check if the outputted cv::Mat is correct. When I run the save_mat() function however, the program crashes.
It is not recommended to store device context handles. For example a call to GetDC should be followed by ReleaseDC as soon as you are finished with the handle. You can store bitmap handles and memory dc, but in most cases it is not necessary.
Once you have copied the image in to bitmap, use GetDIBits to copy the bits in to cv::Mat as shown in the example below.
Note that your application needs DPI compatibility, for example with SetProcessDPIAware to find the correct desktop size.
This example uses 32-bit bitmap with CV_8UC4, but these GDI functions are 24-bit. You can also use 24-bit bitmap with CV_8UC3.
void screenshot()
{
auto w = GetSystemMetrics(SM_CXFULLSCREEN);
auto h = GetSystemMetrics(SM_CYFULLSCREEN);
auto hdc = GetDC(HWND_DESKTOP);
auto hbitmap = CreateCompatibleBitmap(hdc, w, h);
auto memdc = CreateCompatibleDC(hdc);
auto oldbmp = SelectObject(memdc, hbitmap);
BitBlt(memdc, 0, 0, w, h, hdc, 0, 0, SRCCOPY);
cv::Mat mat(h, w, CV_8UC4);
BITMAPINFOHEADER bi = { sizeof(bi), w, -h, 1, 32, BI_RGB };
GetDIBits(hdc, hbitmap, 0, h, mat.data, (BITMAPINFO*)&bi, DIB_RGB_COLORS);
cv::imwrite("screenshot.png", mat);
SelectObject(memdc, oldbmp);
DeleteDC(memdc);
DeleteObject(hbitmap);
ReleaseDC(HWND_DESKTOP, hdc);
}
I have a call to CreateDIBSection() which is returning 0. The documentation says that this means that "One or more of the input parameters is invalid" but there is no indication of which parameter is invalid.
I had a look that this SO question in which the question ends with "after CreateDIBSection I found the error code is 8, no enough resource" - this confused me - there is no mention of any error codes in the documentation. How did the the poster get this extra information?
EDIT: As requested, here is my code - I must apologise it is not complete - it is part of a huge program, and making a minimal winapi program is not trivial.
HDC hdcTemp;
BYTE* bitPointer;
hdcTemp = CreateCompatibleDC(hdc_desktop);
my_printf("GetDeviceCaps(hdcTemp,BITSPIXEL) = %d\n",GetDeviceCaps(hdcTemp,BITSPIXEL)); // this prints "32"
static BITMAPINFO bitmap;
bitmap.bmiHeader.biSize = sizeof(bitmap.bmiHeader);
bitmap.bmiHeader.biWidth = 280;
bitmap.bmiHeader.biHeight = height_to_check;
bitmap.bmiHeader.biPlanes = 1;
bitmap.bmiHeader.biBitCount = 32;
bitmap.bmiHeader.biCompression = BI_RGB;
bitmap.bmiHeader.biSizeImage = 280 * 4 * height_to_check;
bitmap.bmiHeader.biClrUsed = 0;
bitmap.bmiHeader.biClrImportant = 0;
HBITMAP hBitmap2 = CreateDIBSection(hdcTemp, &bitmap, DIB_RGB_COLORS, (void**)(&bitPointer), NULL, NULL);
change to
BYTE* bitPointer;
HDC hdcScreen = GetDC(NULL);
static BITMAPINFO bitmap;
bitmap.bmiHeader.biSize = sizeof(bitmap.bmiHeader);
bitmap.bmiHeader.biWidth = 280;
bitmap.bmiHeader.biHeight = height_to_check;
bitmap.bmiHeader.biPlanes = 1;
bitmap.bmiHeader.biBitCount = 32;
bitmap.bmiHeader.biCompression = BI_RGB;
bitmap.bmiHeader.biSizeImage = 280 * 4 * height_to_check;
bitmap.bmiHeader.biClrUsed = 0;
bitmap.bmiHeader.biClrImportant = 0;
HBITMAP hBitmap2 = CreateDIBSection(hdcScreen, &bitmap, DIB_RGB_COLORS, (void**)(&bitPointer), NULL, NULL);
ReleaseDC(NULL, hdcScreen);
i.e. don't pass an HDC returned from CreateCompatibleDC to CreateDIBSection; use the device context of the screen.
Calling CreateCompatibleDC creates the device context with a 1x1 monochrome bitmap associated with it no matter what HDC you passed in so when you create a bitmap or DIB section compatible to that HDC Win32 tries to be compatible with the monochrome bitmap which you dont want.
At present, MSDN points out that "one or more input parameters are invalid" is reasonable. Tests show that if the bitmap size is too large or the input value is invalid, such as zero, NULL will be returned.
I would like to get the context of my window into a bitmap. I use the window to draw basic lines with touch. The problem that I'm having is my bitmap is black. Which it is probably due to the fact that I'm not grabbing the device context properly or doing something else wrong.
The functions CreateBitmapInfoStruct and CreateBMPFile are from this MSDN example.
Also note that g_hWnd is a global variable that has the handle of the window for which I want to save the picture.
My end goal is to be able to save the bitmap into a mysql field (BLOB) that I have. This is what my original problem was. Anyway, I started by first trying to create a BMP to file.
I have searched here and in other places. The best solution I found was recommended here following this MSDN example. However, it is not working.
Any help for this specific problem and/or in writing to the bitmap into a blob into mysql table, will be greatly appreciated.
Here is my code:
HDC hDC = GetDC(g_hWnd);
LPRECT rect = (LPRECT)malloc(sizeof(RECT));
GetWindowRect(g_hWnd,rect);
int h = rect->right - rect->left;
int w = rect->bottom - rect->top;
LPRECT rect = (LPRECT)malloc(sizeof(RECT));
GetWindowRect(g_hWnd,rect);
HBITMAP hBmp = CreateCompatibleBitmap(hDC,w,h);
PBITMAPINFO pbmi;
pbmi = CreateBitmapInfoStruct(g_hWnd,hBmp);
CreateBMPFile(g_hWnd, TEXT("c:\\TEMPO\\TestG2.bmp"), pbmi,
hBmp, hDC) ;
ReleaseDC(g_hWnd,hDC);
DeleteObject(hBmp);
DeleteObject(pbmi);
if (rect != nullptr)
free(rect);
EDIT:
The actual answer for capturing the screen (getDC) is to modify this sample in MSDN.
I have modified the sample here (remove the stretch) Note that still uses the goto, which I will remove.
A note about the GOTO... WHile I don't use it, I don't find it to be a problem either. I think too much has been made about the GOTO statement... like if in assembly, we wouldn't do goto (JUMPS)
Here is the code:
void saveBitmap()
{
HDC hdcScreen;
HDC hdcWindow;
HDC hdcMemDC = NULL;
HBITMAP hbmScreen = NULL;
BITMAP bmpScreen;
// Retrieve the handle to a display device context for the client
// area of the window.
hdcScreen = GetDC(NULL);
hdcWindow = GetDC(g_hWnd);
// Create a compatible DC which is used in a BitBlt from the window DC
hdcMemDC = CreateCompatibleDC(hdcWindow);
if(!hdcMemDC)
{
goto done;
}
RECT rcClient;
GetClientRect(g_hWnd, &rcClient);
hbmScreen = CreateCompatibleBitmap(hdcWindow, rcClient.right-rcClient.left,
rcClient.bottom-rcClient.top);
if(!hbmScreen)
{
goto done;
}
SelectObject(hdcMemDC,hbmScreen);
if(!BitBlt(hdcMemDC,
0,0,
rcClient.right-rcClient.left, rcClient.bottom-rcClient.top,
hdcWindow,
0,0,
SRCCOPY))
{
goto done;
}
GetObject(hbmScreen,sizeof(BITMAP),&bmpScreen);
BITMAPFILEHEADER bmfHeader;
BITMAPINFOHEADER bi;
bi.biSize = sizeof(BITMAPINFOHEADER);
bi.biWidth = bmpScreen.bmWidth;
bi.biHeight = bmpScreen.bmHeight;
bi.biPlanes = 1;
bi.biBitCount = 32;
bi.biCompression = BI_RGB;
bi.biSizeImage = 0;
bi.biXPelsPerMeter = 0;
bi.biYPelsPerMeter = 0;
bi.biClrUsed = 0;
bi.biClrImportant = 0;
DWORD dwBmpSize = ((bmpScreen.bmWidth * bi.biBitCount + 31) / 32) * 4 *
bmpScreen.bmHeight;
// Starting with 32-bit Windows, GlobalAlloc and LocalAlloc are implemented as wrapper functions that
// call HeapAlloc using a handle to the process's default heap. Therefore, GlobalAlloc and LocalAlloc
// have greater overhead than HeapAlloc.
HANDLE hDIB = GlobalAlloc(GHND,dwBmpSize);
char *lpbitmap = (char *)GlobalLock(hDIB);
// Gets the "bits" from the bitmap and copies them into a buffer
// which is pointed to by lpbitmap.
GetDIBits(hdcWindow, hbmScreen, 0,
(UINT)bmpScreen.bmHeight,
lpbitmap,
(BITMAPINFO *)&bi, DIB_RGB_COLORS);
// A file is created, this is where we will save the screen capture.
HANDLE hFile = CreateFile(L"c:\\tempo\\captureqwsx.bmp",
GENERIC_WRITE,
0,
NULL,
CREATE_ALWAYS,
FILE_ATTRIBUTE_NORMAL, NULL);
// Add the size of the headers to the size of the bitmap to get the total file size
DWORD dwSizeofDIB = dwBmpSize + sizeof(BITMAPFILEHEADER) +
sizeof(BITMAPINFOHEADER);
//Offset to where the actual bitmap bits start.
bmfHeader.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER) +
(DWORD)sizeof(BITMAPINFOHEADER);
//Size of the file
bmfHeader.bfSize = dwSizeofDIB;
//bfType must always be BM for Bitmaps
bmfHeader.bfType = 0x4D42; //BM
DWORD dwBytesWritten = 0;
WriteFile(hFile, (LPSTR)&bmfHeader, sizeof(BITMAPFILEHEADER), &dwBytesWritten, NULL);
WriteFile(hFile, (LPSTR)&bi, sizeof(BITMAPINFOHEADER), &dwBytesWritten, NULL);
WriteFile(hFile, (LPSTR)lpbitmap, dwBmpSize, &dwBytesWritten, NULL);
//Unlock and Free the DIB from the heap
GlobalUnlock(hDIB);
GlobalFree(hDIB);
//Close the handle for the file that was created
CloseHandle(hFile);
//Clean up
done:
DeleteObject(hbmScreen);
DeleteObject(hdcMemDC);
ReleaseDC(NULL,hdcScreen);
ReleaseDC(g_hWnd,hdcWindow);
}
You can use GetDIBits().
This function copies the image pixels data into your own allocated memory.
See GetDIBits and loop through pixels using X, Y for some more details and explanation.
I wish to create a transparent window over the desktop.
For that purpose I've created an HDC with a background of the desktop (created HBITMAP of the desktop and applied it to my HDC), and invoked UpdateLayeredWindow.
So far, so good.
for performance issues i need to keep a persistent GDI+ object, meaning my HDC and HBITMAP need to stay the same handles between paintings (assuming the desktop DC didn't change), same as in this question.
In the first painting iteration all goes well. in the second painting iteration, since the HDC and HBITMAP haven't changed, I repaint on the existing HDC, meaning i get double images (the background is not erased).
Here's a code example of what I'm doing:
bool SomeUI::Draw()
{
BLENDFUNCTION blend = {0};
POINT ptPos = {0};
SIZE sizeWnd = {0};
POINT ptSrc = {0};
BOOL bUpdate = FALSE;
// Get the client rect
RECT rctWindow;
bool bGot = GetWindowRect(rctWindow);
if (!bGot)
return false;
// Get the desktop's device context
HDC hDCDesktop = GetDC(NULL);
if (!hDCDesktop)
return false;
int nWidth = abs(rctWindow.right - rctWindow.left);
int nHeight = abs(rctWindow.bottom - rctWindow.top);
// Create 32Bit bitmap to apply PNG transparency
VOID *ppvBits = NULL;
BITMAPINFO BitmapInfo = {0};
BitmapInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
BitmapInfo.bmiHeader.biWidth = nWidth;
BitmapInfo.bmiHeader.biHeight = nHeight;
BitmapInfo.bmiHeader.biPlanes = 1;
BitmapInfo.bmiHeader.biBitCount = 32;
BitmapInfo.bmiHeader.biCompression = BI_RGB;
HBITMAP hBmp = CreateDIBSection(hDCDesktop, &BitmapInfo, DIB_RGB_COLORS, &ppvBits, NULL, 0);
if (!hBmp || hBmp==(HBITMAP)ERROR_INVALID_PARAMETER)
goto releaseHandles;
// Create a compatible DC and select the newly created bitmap
if (!m_hDC)
{
m_hDC = CreateCompatibleDC(hDCDesktop);
if (!m_hDC)
goto releaseHandles;
SelectObject(m_hDC, hBmp);
}
else
{
///////////////////////////////////////////////////////////////////////
//
// The problem lies here, this is where I need to reset the HBITMAP
// according to the desktop here (to have a transparent DC to work on)
//
///////////////////////////////////////////////////////////////////////
}
// The drawing logic
bool bInnerDraw = Draw(m_hDC);
if (!bInnerDraw)
goto releaseHandles;
// Call UpdateLayeredWindow
blend.BlendOp = AC_SRC_OVER;
blend.SourceConstantAlpha = 255;
blend.AlphaFormat = AC_SRC_ALPHA;
sizeWnd.cx = nWidth;
sizeWnd.cy = nHeight;
ptPos.x = rctWindow.left;
ptPos.y = rctWindow.top;
bUpdate = UpdateLayeredWindow(m_hWnd, hDCDesktop, &ptPos, &sizeWnd, m_hDC, &ptSrc, 0, &blend, ULW_ALPHA);
if (!bUpdate)
goto releaseHandles;
releaseHandles:
// releasing handles
}
Any ideas?
Found the Answer:
In order to reset the persistent HBITMAP, (reminder: it needs to stay the same handle), we'll set the desktop background of that area to a temporary HBITMAP and copy it to the persistent HBITMAP.
To achieve that (copying from one HBITMAP to the other), We'll create a temporary HDC and select the temporary HBITMAP to it, and copy the temporary HDC to the persistent HDC, usint BitBlt
Here's the code:
hBmpTemp = CreateDIBSection(hDCDesktop, &BitmapInfo, DIB_RGB_COLORS, &ppvBits, NULL, 0);
if (!hBmpTemp || hBmpTemp==(HBITMAP)ERROR_INVALID_PARAMETER)
goto releaseHandles;
HDC hTempDC = CreateCompatibleDC(NULL);
if (!hTempDC)
goto releaseHandles;
SelectObject(hTempDC, hBmpTemp);
::BitBlt(m_hPersistentDC, 0, 0, nWidth, nHeight, hTempDC, rctWindow.left, rctWindow.top, SRCCOPY);
::DeleteDC(hTempDC);
I want to read a rectangular area, or whole screen pixels. As if screenshot button was pressed.
How i do this?
Edit: Working code:
void CaptureScreen(char *filename)
{
int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
HWND hDesktopWnd = GetDesktopWindow();
HDC hDesktopDC = GetDC(hDesktopWnd);
HDC hCaptureDC = CreateCompatibleDC(hDesktopDC);
HBITMAP hCaptureBitmap = CreateCompatibleBitmap(hDesktopDC, nScreenWidth, nScreenHeight);
SelectObject(hCaptureDC, hCaptureBitmap);
BitBlt(hCaptureDC, 0, 0, nScreenWidth, nScreenHeight, hDesktopDC, 0,0, SRCCOPY|CAPTUREBLT);
BITMAPINFO bmi = {0};
bmi.bmiHeader.biSize = sizeof(bmi.bmiHeader);
bmi.bmiHeader.biWidth = nScreenWidth;
bmi.bmiHeader.biHeight = nScreenHeight;
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 32;
bmi.bmiHeader.biCompression = BI_RGB;
RGBQUAD *pPixels = new RGBQUAD[nScreenWidth * nScreenHeight];
GetDIBits(
hCaptureDC,
hCaptureBitmap,
0,
nScreenHeight,
pPixels,
&bmi,
DIB_RGB_COLORS
);
// write:
int p;
int x, y;
FILE *fp = fopen(filename, "wb");
for(y = 0; y < nScreenHeight; y++){
for(x = 0; x < nScreenWidth; x++){
p = (nScreenHeight-y-1)*nScreenWidth+x; // upside down
unsigned char r = pPixels[p].rgbRed;
unsigned char g = pPixels[p].rgbGreen;
unsigned char b = pPixels[p].rgbBlue;
fwrite(fp, &r, 1);
fwrite(fp, &g, 1);
fwrite(fp, &b, 1);
}
}
fclose(fp);
delete [] pPixels;
ReleaseDC(hDesktopWnd, hDesktopDC);
DeleteDC(hCaptureDC);
DeleteObject(hCaptureBitmap);
}
Starting with your code and omitting error checking ...
// Create a BITMAPINFO specifying the format you want the pixels in.
// To keep this simple, we'll use 32-bits per pixel (the high byte isn't
// used).
BITMAPINFO bmi = {0};
bmi.bmiHeader.biSize = sizeof(bmi.bmiHeader);
bmi.bmiHeader.biWidth = nScreenWidth;
bmi.bmiHeader.biHeight = nScreenHeight;
bmi.bmiHeader.biPlanes = 1;
bmi.bmiHeader.biBitCount = 32;
bmi.bmiHeader.biCompression = BI_RGB;
// Allocate a buffer to receive the pixel data.
RGBQUAD *pPixels = new RGBQUAD[nScreenWidth * nScreenHeight];
// Call GetDIBits to copy the bits from the device dependent bitmap
// into the buffer allocated above, using the pixel format you
// chose in the BITMAPINFO.
::GetDIBits(hCaptureDC,
hCaptureBitmap,
0, // starting scanline
nScreenHeight, // scanlines to copy
pPixels, // buffer for your copy of the pixels
&bmi, // format you want the data in
DIB_RGB_COLORS); // actual pixels, not palette references
// You can now access the raw pixel data in pPixels. Note that they are
// stored from the bottom scanline to the top, so pPixels[0] is the lower
// left pixel, pPixels[1] is the next pixel to the right,
// pPixels[nScreenWidth] is the first pixel on the second row from the
// bottom, etc.
// Don't forget to free the pixel buffer.
delete [] pPixels;
Rereading your question, it sounds like we may have gotten off on a tangent with the screen capture. If you just want to check some pixels on the screen, you can use GetPixel.
HDC hdcScreen = ::GetDC(NULL);
COLORREF pixel = ::GetPixel(hdcScreen, x, y);
ReleaseDC(NULL, hdcScreen);
if (pixel != CLR_INVALID) {
int red = GetRValue(pixel);
int green = GetGValue(pixel);
int blue = GetBValue(pixel);
...
} else {
// Error, x and y were outside the clipping region.
}
If you're going to read a lot of pixels, then you're better off with a screen capture and then using GetDIBits. Calling GetPixel zillions of times will be slow.
You make a screenshot with BitBlt(). The size of the shot is set with the nWidth and nHeight arguments. The upper left corner is set with the nXSrc and nYSrc arguments.
You can use the code below to read the screen pixels:
HWND desktop = GetDesktopWindow();
HDC desktopHdc = GetDC(desktop);
COLORREF color = GetPixel(desktopHdc, x, y);
HBITMAP is not a pointer or an array, it is a handle that is managed by Windows and has meaning only to Windows. You must ask Windows to copy the pixels somewhere for use.
To get an individual pixel value, you can use GetPixel without even needing a bitmap. This will be slow if you need to access many pixels.
To copy a bitmap to memory you can access, use the GetDIBits function.