CreateCompitableDC的小问题

[greensleeve]

为什么我在创建一个CDC时（用CreateCompitableDC()}有时会出错？

[greensleeve]

anybody know?

[VegetableBird]

代码贴出来看看好吗？

[prog_st]

Creates a memory device context that is compatible with the device specified by pDC. A memory device context is a block of memory that represents a display surface. It can be used to prepare images in memory before copying them to the actual device surface of the compatible device.

When a memory device context is created, GDI automatically selects a 1-by-1 monochrome stock bitmap for it. GDI output functions can be used with a memory device context only if a bitmap has been created and selected into that context.

This function can only be used to create compatible device contexts for devices that support raster operations. See the CDC::BitBlt member function for information regarding bit-block transfers between device contexts. To determine whether a device context supports raster operations, see the RC_BITBLT raster capability in the member function CDC::GetDeviceCaps.

Example

// This OnDraw() handler loads a bitmap from system resources,
// centers it in the view, and uses BitBlt() to paint the bitmap
// bits.

void CBlat2View::OnDraw(CDC* pDC)
{
CBlat2Doc* pDoc = GetDocument();
ASSERT_VALID(pDoc);

// load IDB_BITMAP1 from our resources
CBitmap bmp;
if (bmp.LoadBitmap(IDB_BITMAP1))
{
// Get the size of the bitmap
BITMAP bmpInfo;
bmp.GetBitmap(&bmpInfo);

// Create an in-memory DC compatible with the
// display DC we're using to paint
CDC dcMemory;
dcMemory.CreateCompatibleDC(pDC);

// Select the bitmap into the in-memory DC
CBitmap* pOldBitmap = dcMemory.SelectObject(&bmp);

// Find a centerpoint for the bitmap in the client area
CRect rect;
GetClientRect(&rect);
int nX = rect.left + (rect.Width() - bmpInfo.bmWidth) / 2;
int nY = rect.top + (rect.Height() - bmpInfo.bmHeight) / 2;

// Copy the bits from the in-memory DC into the on-
// screen DC to actually do the painting. Use the centerpoint
// we computed for the target offset.
pDC->BitBlt(nX, nY, bmpInfo.bmWidth, bmpInfo.bmHeight, &dcMemory,
0, 0, SRCCOPY);

dcMemory.SelectObject(pOldBitmap);
}
else
TRACE0("ERROR: Where's IDB_BITMAP1?\n");
}