PRB: Memory DC Produces Monochrome Images (139165)
The information in this article applies to:
- Microsoft Windows Software Development Kit (SDK) 3.1, when used with:
- Microsoft Win32 Application Programming Interface (API)
This article was previously published under Q139165 SYMPTOMS
When you create and use a memory Device Context (DC) to draw and store GDI
images, the bitmap displayed when transferred from the memory device
context to the physical display is monochrome. All colors are converted to
either black or white.
CAUSE
When creating a compatible bitmap for the memory DC, the handle to the
memory DC is used as the first parameter to the call to
CreateCompatibleBitmap(). This create a monochrome bitmap because a
memory DC created with CreateCompatibleDC() is given a 1x1 monochrome bitmap as its default bitmap.
For example, the following code creates a monochrome bitmap and selects it
into a memory DC:
HDC hdc, hdcMem;
HBITMAP hBitmap;
hdc = GetDC(hWnd);
hdcMem = CreateCompatibleDC(hdc);
hBitmap = CreateCompatibleBitmap(hdcMem, 400, 400);
SelectObject(hdcMem, hBitmap);
SetTextColor(hdcMem, RGB(0, 0, 255));
RESOLUTION
Send a physical screen DC to the CreateCompatibleBitmap() function rather than the memory DC that you plan on selecting the bitmap into.
The following example code properly sets up a color memory DC with a color
bitmap with the same bit depth as the physical display:
HDC hdc, hdcMem;
HBITMAP hBitmap;
hdc = GetDC(hWnd);
hdcMem = CreateCompatibleDC(hdc);
hBitmap = CreateCompatibleBitmap(hdc, 400, 400);
SelectObject(hdcMem, hBitmap);
SetTextColor(hdcMem, RGB(0, 0, 255));
STATUS
This behavior is by design.
| Modification Type: | Minor | Last Reviewed: | 3/21/2005 |
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| Keywords: | kbcode kbprb KB139165 |
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