Thread: Create a bitmat from just an hDC?

I know it should be possible, I need to be able to create a bitmap from just an hDC. How would I go about doing this? The bitmap will be stored in memory and not saved anywhere. Basically I want my function to just return a handle to the bitmap.

I want to do something similar to this http://www.codeproject.com/KB/vb-int...shotInVB6.aspx. But unfortunatly due to the way the program is setup, the only data coming in is the DC of the device that Im taking the screenshot of.

Is this what you need??

Code:

#include <windows.h>

#define BITMAPSIZE  120

LRESULT CALLBACK MyWndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam);

DWORD* dwBitmapArray;
BITMAPINFO bmInfo;
HBITMAP theBitmapFromHDC;
HDC theCompatibleDC;
BYTE bRed = 0xff;
BYTE bGreen = 0x00;
BYTE bBlue = 0x00;

char szClassName[ ] = "BMPfromHDC";

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
    WNDCLASS wc;
    HWND hwnd;
    MSG msg;

    ZeroMemory(&wc, sizeof(WNDCLASS));
    wc.hInstance = hInstance;
    wc.lpfnWndProc = MyWndProc;
    wc.lpszClassName = szClassName;
    wc.hbrBackground = (HBRUSH) COLOR_BACKGROUND;
    RegisterClass(&wc);

    hwnd = CreateWindowEx (
        0,    
        szClassName,  
        "BMP from HDC Application",  
        WS_OVERLAPPEDWINDOW, 
        CW_USEDEFAULT,       
        CW_USEDEFAULT,       
        450,                 
        450,                 
        HWND_DESKTOP,        
        NULL,                
        hInstance,       
        NULL                 
        );
    ShowWindow (hwnd, nShowCmd);
    while(GetMessage(&msg, hwnd, 0,0))
        DispatchMessage(&msg);
    return 0;
}

LRESULT CALLBACK MyWndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam)
{
    PAINTSTRUCT ps;
    int iIndex;
    switch(msg)
    {
        case WM_CREATE:
            dwBitmapArray = (DWORD*) malloc(BITMAPSIZE*BITMAPSIZE*sizeof(DWORD));
            for(iIndex = 0; iIndex < BITMAPSIZE * BITMAPSIZE; iIndex++)
                dwBitmapArray[iIndex] = (bRed << 16) | (bGreen << 8) | (bBlue);
            ZeroMemory(&bmInfo, sizeof(BITMAPINFO));
            bmInfo.bmiHeader.biBitCount = 32;
            bmInfo.bmiHeader.biHeight = BITMAPSIZE;
            bmInfo.bmiHeader.biPlanes = 1;
            bmInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
            bmInfo.bmiHeader.biWidth = BITMAPSIZE;
            bmInfo.bmiHeader.biCompression = BI_RGB;
            theBitmapFromHDC = CreateCompatibleBitmap(GetDC(hwnd), BITMAPSIZE, BITMAPSIZE);
            theCompatibleDC = CreateCompatibleDC(GetDC(hwnd));
            SelectObject(theCompatibleDC, theBitmapFromHDC);
            SetDIBits(theCompatibleDC, theBitmapFromHDC, 0, BITMAPSIZE, dwBitmapArray, &bmInfo, 0);
            break;
        case WM_PAINT:
            BeginPaint(hwnd, &ps);
            BitBlt(ps.hdc, 0, 0, BITMAPSIZE, BITMAPSIZE, theCompatibleDC, 0, 0, SRCCOPY);
            EndPaint(hwnd, &ps);
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            exit(0);
            break;
        default:
            return DefWindowProc(hwnd, msg, wparam, lparam);
    }
    return lparam;
}

You cant create a bitmap from an HDC, they are two different concepts. a bitmap is an image, an HDC is a handle to a device context, usually for the video display. Basically its a special purpose pointer to the display interface, but not to the frme buffer or anything in particular, its shoudl be treated as logically opaque.

Originally Posted by BobS0327

Is this what you need??

No, as the question has no sense at all..
A HDC is just used to select a bitmap.

Originally Posted by novacain

Couldn't you use the HDC to create a compatible HDC,
create a compatible BMP,
select the BMP into the created HDC (catching the original BMP),
use bitblt to copy the image to your created BMP?

Then selecting the orginal BMP frees your bitmap from the HDC, leaving only the clean up.

This was kind of what I was wondering. Because BitBlt only needs the HDC, a width, and a height. I was just wondering if there was any way to get a height without having the hwnd. I know it won't work always, but for my purposes it would be good enough.

So from another POV would there be any way to determine a width and a height of some image on the HDC. Is there like a value that is always returned when you go out of bounds our something?

Originally Posted by novacain

GetObject() with BITMAP struct will get the height and width (and other data) of the bitmap.

This will require you to 'push' the BMP out of the original HDC. This is done by creating a temp BMP, compatible with the original HDC and then use SelectObject(), catching the HBITMAP returned.

You can then call GetObject() on the HBITMAP, filling the BITMAP struct
SelectObject() the HBITMAP back into the original HDC
DeleteObject() the temp BMP you created.

Note that the temp BMP is only used to 'push' the BMP of interest out of the HDC while you get data from it.

Now create your compatible HDC
compatible BMP using the size
etc.....

Will that work on, say, an opengl window. Or a DX window? (I know, now Im just being lazy, I could test this for myself)

Well, I think if you actually ever read the MSDN docs you'd not even need to ask the question without performing some sort of test. But since I see this is only your fifth post and you already have described yourself as being too lazy to try something, I will just let you take this opportunity to not be lazy and to try it out on your own.