OK I seem to have found the cause just by sheer luck and its nothing wrong with that particular method, it's further back up the call stack.
Earlier I resize the image and as part of that method I return the resized object as follows. I have inserted two calls to the above method and a direct save to a file.
// At this point the new bitmap has no MimeType
// Need to output to memory stream
using (var m = new MemoryStream())
{
dst.Save(m, format);
var img = Image.FromStream(m);
//TEST
img.Save("C:\\test.jpg");
var bytes = PhotoEditor.ConvertImageToByteArray(img);
return img;
}
It appears that the memory stream that the object was created on has to be open at the time the object is saved. I am not sure why this is. Is anyone able to enlighten me and how I can get around this.
I only return from a stream because after using the resize code similar to this the destination file has an unknown mime type (img.RawFormat.Guid) and Id like the Mime type to be correct on all image objects as it makes it hard write generic handling code otherwise.
EDIT
This didn't come up in my initial search but here's the answer from Jon Skeet
The only way I know of that may (or may not) do what you are looking for is to create the window with the CS_OWNDC class style.
What that does is allocates a unique device context for each window in the class.
Edit
From the linked MSDN article:
A device context is a special set of
values that applications use for
drawing in the client area of their
windows. The system requires a device
context for each window on the display
but allows some flexibility in how the
system stores and treats that device
context.
If no device-context style is
explicitly given, the system assumes
each window uses a device context
retrieved from a pool of contexts
maintained by the system. In such
cases, each window must retrieve and
initialize the device context before
painting and free it after painting.
To avoid retrieving a device context
each time it needs to paint inside a
window, an application can specify the
CS_OWNDC style for the window class.
This class style directs the system to
create a private device context — that
is, to allocate a unique device
context for each window in the class.
The application need only retrieve the
context once and then use it for all
subsequent painting.
Windows 95/98/Me: Although the
CS_OWNDC style is convenient, use it
carefully, because each device context
uses a significant portion of 64K GDI
heap.
Perhaps this example will illustrate the use of CS_OWNDC better:
#include <windows.h>
static TCHAR ClassName[] = TEXT("BitmapWindow");
static TCHAR WindowTitle[] = TEXT("Bitmap Window");
HDC m_hDC;
HWND m_hWnd;
LRESULT CALLBACK WndProc(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
static PAINTSTRUCT ps;
switch (msg)
{
case WM_PAINT:
{
BeginPaint(hWnd, &ps);
if (ps.hdc == m_hDC)
MessageBox(NULL, L"ps.hdc == m_hDC", WindowTitle, MB_OK);
else
MessageBox(NULL, L"ps.hdc != m_hDC", WindowTitle, MB_OK);
if (ps.hdc == GetDC(hWnd))
MessageBox(NULL, L"ps.hdc == GetDC(hWnd)", WindowTitle, MB_OK);
else
MessageBox(NULL, L"ps.hdc != GetDC(hWnd)", WindowTitle, MB_OK);
RECT r;
SetRect(&r, 10, 10, 50, 50);
FillRect(m_hDC, &r, (HBRUSH) GetStockObject( BLACK_BRUSH ));
EndPaint(hWnd, &ps);
return 0;
}
case WM_DESTROY:
{
PostQuitMessage(0);
return 0;
}
}
return DefWindowProc(hWnd, msg, wParam, lParam);
}
int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nShowCmd)
{
WNDCLASSEX wcex;
wcex.cbClsExtra = 0;
wcex.cbSize = sizeof(WNDCLASSEX);
wcex.cbWndExtra = 0;
wcex.hbrBackground = (HBRUSH) GetStockObject( WHITE_BRUSH );
wcex.hCursor = LoadCursor( NULL, IDC_ARROW );
wcex.hIcon = LoadIcon( NULL, IDI_APPLICATION );
wcex.hIconSm = NULL;
wcex.hInstance = hInstance;
wcex.lpfnWndProc = WndProc;
wcex.lpszClassName = ClassName;
wcex.lpszMenuName = NULL;
wcex.style = CS_OWNDC;
if (!RegisterClassEx(&wcex))
return 0;
DWORD dwExStyle = 0;
DWORD dwStyle = WS_OVERLAPPEDWINDOW | WS_VISIBLE;
m_hWnd = CreateWindowEx(dwExStyle, ClassName, WindowTitle, dwStyle, 0, 0, 300, 300, NULL, NULL, hInstance, NULL);
if (!m_hWnd)
return 0;
m_hDC = GetDC(m_hWnd);
MSG msg;
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return msg.wParam;
}
The CS_OWNDC flag is not to be confused with the CS_CLASSDC flag which:
Allocates one device context to be shared by all windows in the class. Because window classes are process specific, it is possible for multiple threads of an application to create a window of the same class. It is also possible for the threads to attempt to use the device context simultaneously. When this happens, the system allows only one thread to successfully finish its drawing operation.
If all else fails just reconstruct the CachedBitmap.
When you construct a CachedBitmap object, you must pass the address of a Graphics object to the constructor. If the screen associated with that Graphics object has its bit depth changed after the cached bitmap is constructed, then the DrawCachedBitmap method will fail, and you should reconstruct the cached bitmap. Alternatively, you can hook the display change notification message and reconstruct the cached bitmap at that time.
I'm not saying that CS_OWNDC is the perfect solution, but it is one step towards a better solution.
Edit
The sample program seemed to retain the same DC during screen resolution / bit depth change testing with the CS_OWNDC flag, however, when that flag was removed, the DC's were different (Window 7 64-bit Ultimate)(should work the same over differn OS versions... although it wouldn't hurt to test).
Edit2
This example doesn't call GetUpdateRect to check if the window needs to be painted during the WM_PAINT. That is an error.
Best Answer
Hmm... The filling capabilities are determined by the target device. When working over remote desktop, AFAIK Windows substitutes the display driver, so that can change the supported features of the display.