unable to read bitmap data from hBitmap

heckubiss

I am using the bitmapdata function in gdiplus to quickly get the pixel color info from a bitmap. It works when I load a bitmap from a file but it doesnt work when I use fromHbitmap where hBitmap contains a screencapture. when I use fromHbitmap, the resulting data is blank.

here is my code

#include
#include
#include
using namespace Gdiplus;



INT main()
{
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);



HDC hDDC = GetDC( GetDesktopWindow() );


HBITMAP hBitmap = CreateCompatibleBitmap(hDDC, 500, 500);



HPALETTE hPalette = (HPALETTE)GetCurrentObject(hDDC, OBJ_PAL);

Bitmap* bitmap = Bitmap::FromHBITMAP (hBitmap,hPalette); // when I change this line to Bitmap* bitmap = new Bitmap(L"D:my_picture.jpg"); it works

BitmapData* bitmapData = new BitmapData;
Rect rect(0, 0, 100, 100);

// Lock a 100x100 rectangular portion of the bitmap for reading.
bitmap->LockBits(
&rect,
ImageLockModeRead,
PixelFormat32bppARGB,
bitmapData);

printf("The stride is %d.

", bitmapData->Stride);

// Display the hexadecimal value of each pixel in the 100x100 rectangle.
UINT* pixels = (UINT*)bitmapData->Scan0;

for(UINT row = 0; row < 100; ++row)
{
for(UINT col = 0; col < 100; ++col)
{
printf("%x
", pixels[row * bitmapData->Stride / 4 + col]);
}
printf("- - - - - - - - - -
");
}

bitmap->UnlockBits(bitmapData);
delete bitmapData;
delete bitmap;
DeleteObject(hBitmap);
GdiplusShutdown(gdiplusToken);
return 0;
}

richfell

I believe the root of your issue is that you are not creating a screen capture with these lines:

HDC hDDC = GetDC( GetDesktopWindow() );
HBITMAP hBitmap = CreateCompatibleBitmap(hDDC, 500, 500);

What you are doing is creating a new "empty" bitmap which is compatible with the color settings of the desktop's Device Context.

In order to get a screen capture you would have to get the desktop window to paint itself into your compatible bitmap by setting up a DeviceContext with your new bitmap and sending a WM_PAINT message to the desktop window supplying your bitmap's DeviceContext handle as the wParam.

Something like:

// get desktop window handle
HWND hWndDesktop = GetDesktopWindow();

// get the window rectangle
RECT desktopRect;
GetWindowRect(hWndDesktop, &desktopRect);

// calculate width/height of the desktop window
int dtWidth = desktopRect.right - desktopRect.left;
int dtHeight = desktopRect.bottom - desktopRect.top;

// create a compatible DC and bitmap
HDC hDDC = CreateCompatibleDC(GetDC(hWndDesktop));
BITMAP hBitmap = CreateCompatibleBitmap(hDDC, dtWidth, dtHeight);

// select the bitmap into the compatible DC
SelectObject(hDDC, hBitmap);

// have the desktop paint itself into our bitmap
SendMessage(hWndDesktop, WM_PAINT, (WPARAM)hDDC, 0);

AsmGuru62

[color=Blue]All correct, just instead of sending WM_PAINT use BitBlt() from desktop DC to memory DC.[/color]

heckubiss

I used bitblt to copy the hDC into the hDDC but the pixel data is still blank

#include
#include
#include
using namespace Gdiplus;


INT main()
{
GdiplusStartupInput gdiplusStartupInput;
ULONG_PTR gdiplusToken;
GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);

HWND hWndDesktop = GetDesktopWindow();
HDC hDC;
hDC=GetDC(hWndDesktop);
// get the window rectangle
RECT desktopRect;
GetWindowRect(hWndDesktop, &desktopRect);

// calculate width/height of the desktop window
int dtWidth = desktopRect.right - desktopRect.left;
int dtHeight = desktopRect.bottom - desktopRect.top;


HDC hDDC = CreateCompatibleDC(hDC);
HBITMAP hBitmap = CreateCompatibleBitmap(hDDC, dtWidth, dtHeight);
SelectObject(hDDC, hBitmap);

BitBlt(hDDC, 0, 0, dtWidth, dtHeight,hDC, 0, 0, SRCCOPY);

HPALETTE hPalette = (HPALETTE)GetCurrentObject(hDDC, OBJ_PAL);
Bitmap* bitmap = Bitmap::FromHBITMAP (hBitmap,hPalette);


BitmapData* bitmapData = new BitmapData;
Rect rect(0, 0, 100, 100);

// Lock a 100x100 rectangular portion of the bitmap for reading.
bitmap->LockBits(
&rect,
ImageLockModeRead,
PixelFormat32bppARGB,
bitmapData);

printf("The stride is %d.

", bitmapData->Stride);

// Display the hexadecimal value of each pixel in the 100x100 rectangle.
UINT* pixels = (UINT*)bitmapData->Scan0;

for(UINT row = 0; row < 100; ++row)
{
for(UINT col = 0; col < 100; ++col)
{
printf("%x
", pixels[row * bitmapData->Stride / 4 + col]);
}
printf("- - - - - - - - - -
");
}

bitmap->UnlockBits(bitmapData);
delete bitmapData;
delete bitmap;
DeleteObject(hBitmap);
GdiplusShutdown(gdiplusToken);




printf("hello world");
return 0;

}

AsmGuru62

: I used bitblt to copy the hDC into the hDDC but the pixel data is
: still blank
:
: #include
: #include
: #include
: using namespace Gdiplus;
:
:
: INT main()
: {
: GdiplusStartupInput gdiplusStartupInput;
: ULONG_PTR gdiplusToken;
: GdiplusStartup(&gdiplusToken, &gdiplusStartupInput, NULL);
:
: HWND hWndDesktop = GetDesktopWindow();
: HDC hDC;
: hDC=GetDC(hWndDesktop);
: // get the window rectangle
: RECT desktopRect;
: GetWindowRect(hWndDesktop, &desktopRect);
:
: // calculate width/height of the desktop window
: int dtWidth = desktopRect.right - desktopRect.left;
: int dtHeight = desktopRect.bottom - desktopRect.top;
:
:
: HDC hDDC = CreateCompatibleDC(hDC);
: HBITMAP hBitmap = CreateCompatibleBitmap(hDDC, dtWidth,
: dtHeight);
: SelectObject(hDDC, hBitmap);
:
: BitBlt(hDDC, 0, 0, dtWidth, dtHeight,hDC, 0, 0, SRCCOPY);

[color=Red]COLORREF rgb1 = GetPixel (hDDC, 22, 34);
COLORREF rgb2 = GetPixel (hDDC, 78, 12);
COLORREF rgb3 = GetPixel (hDDC, 74, 45);
//
// Take a few ^^^ pixels from memory DC and check
// if they return real color values. If they are, then
// code below is not doing its work, but the pixels are
// retrieved and inside hDDC.
[/color]
:
: HPALETTE hPalette = (HPALETTE)GetCurrentObject(hDDC, OBJ_PAL);
: Bitmap* bitmap = Bitmap::FromHBITMAP (hBitmap,hPalette);
:
:
: BitmapData* bitmapData = new BitmapData;
: Rect rect(0, 0, 100, 100);
:
: // Lock a 100x100 rectangular portion of the bitmap for reading.
: bitmap->LockBits(
: &rect,
: ImageLockModeRead,
: PixelFormat32bppARGB,
: bitmapData);
:
: printf("The stride is %d.

", bitmapData->Stride);
:
: // Display the hexadecimal value of each pixel in the 100x100
: rectangle.
: UINT* pixels = (UINT*)bitmapData->Scan0;
:
: for(UINT row = 0; row < 100; ++row)
: {
: for(UINT col = 0; col < 100; ++col)
: {
: printf("%x
", pixels[row * bitmapData->Stride / 4 + col]);
: }
: printf("- - - - - - - - - -
");
: }
:
: bitmap->UnlockBits(bitmapData);
: delete bitmapData;
: delete bitmap;
: DeleteObject(hBitmap);
: GdiplusShutdown(gdiplusToken);
:
:
:
:
: printf("hello world");
: return 0;
:
: }