SetBkMode function

The SetBkMode function sets the background mix mode of the specified device context. The background mix mode is used with text, hatched brushes, and pen styles that are not solid lines.

Syntax

int SetBkMode(
  HDC hdc,
  int mode
);

Parameters

hdc

A handle to the device context.

mode

The background mode. This parameter can be one of the following values.

Value Meaning
OPAQUE
Background is filled with the current background color before the text, hatched brush, or pen is drawn.
TRANSPARENT
Background remains untouched.

Return Value

If the function succeeds, the return value specifies the previous background mode.

If the function fails, the return value is zero.

Remarks

The SetBkMode function affects the line styles for lines drawn using a pen created by the CreatePen function. SetBkMode does not affect lines drawn using a pen created by the ExtCreatePen function.

Examples

To see how to make the background of a hatch brush transparent or opaque, refer to the example shown in the CreateHatchBrush topic.

The next example draws a string 36 times, rotating it 10 degrees counterclockwise each time. It also sets the background mode to transparent to make the text visible.

#include "strsafe.h"
LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    int wmId, wmEvent;
    PAINTSTRUCT ps;
    HDC hdc;

    switch (message)
    {
    
    case WM_PAINT:
        {
        hdc = BeginPaint(hWnd, &ps);
        RECT rc; 
        int angle; 
        HGDIOBJ hfnt, hfntPrev; 
        WCHAR lpszRotate[22] = TEXT("String to be rotated.");
        HRESULT hr; 
        size_t pcch = 22;
 
// Allocate memory for a LOGFONT structure. 
 
PLOGFONT plf = (PLOGFONT) LocalAlloc(LPTR, sizeof(LOGFONT)); 
 
 
// Specify a font typeface name and weight. 
 
hr = StringCchCopy(plf->lfFaceName, 6, TEXT("Arial"));
if (FAILED(hr))
{
// TODO: write error handler
}

plf->lfWeight = FW_NORMAL; 
 
// Retrieve the client-rectangle dimensions. 
 
GetClientRect(hWnd, &rc); 
 
// Set the background mode to transparent for the 
// text-output operation. 
 
SetBkMode(hdc, TRANSPARENT); 
 
// Draw the string 36 times, rotating 10 degrees 
// counter-clockwise each time. 
 
for (angle = 0; angle < 3600; angle += 100) 
{ 
    plf->lfEscapement = angle; 
    hfnt = CreateFontIndirect(plf); 
    hfntPrev = SelectObject(hdc, hfnt);
    
    //
    // The StringCchLength call is fitted to the lpszRotate string
    //
    hr = StringCchLength(lpszRotate, 22, &pcch);
    if (FAILED(hr))
    {
    // TODO: write error handler
    } 
    TextOut(hdc, rc.right / 2, rc.bottom / 2, 
        lpszRotate, pcch); 
    SelectObject(hdc, hfntPrev); 
    DeleteObject(hfnt); 
} 
 
// Reset the background mode to its default. 
 
SetBkMode(hdc, OPAQUE); 
 
// Free the memory allocated for the LOGFONT structure. 
 
LocalFree((LOCALHANDLE) plf); 
        EndPaint(hWnd, &ps);
        break;
        }
    case WM_DESTROY:
        PostQuitMessage(0);
        break;
    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }
    return 0;
}

Requirements

   
Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Target Platform Windows
Header wingdi.h (include Windows.h)
Library Gdi32.lib
DLL Gdi32.dll

See Also

CreatePen

ExtCreatePen

GetBkMode

Painting and Drawing Functions

Painting and Drawing Overview