| Microsoft DirectX 8.1 (C++) |
Constructor method.
Syntax
CDrawImage(
CBaseWindow *pBaseWindow
);
Parameters
pBaseWindow
Pointer to the window where drawing will occur.
Return Value
No return value.
Remarks
This class handles drawing of images through GDI. It works closely in conjunction with the CImageAllocator and CBaseWindow classes. It must know about the CImageAllocator class, because the draw code provides a faster drawing implementation if the buffers it is handed are created through the Microsoft® Win32® CreateDIBSection function. The image allocator creates this type of sample. It is told whether the buffers are allocated by a CImageAllocator object (or derived class) through the CDrawImage::NotifyAllocator member function.
If the buffers used to draw are not allocated by a compatible allocator, it will draw using the Win32 SetDIBitsToDevice family of APIs. The CBaseWindow class retrieves the window handle where the images are to be drawn. The device contexts that the drawing code should use are passed in through the CDrawImage::SetDrawContext member function.
The CImageAllocator, CImageSample, and CDrawImage classes are all tightly associated. The buffers that the image allocator creates are made using the Win32 CreateDIBSection function. The allocator then creates its own samples (based on the CImageSample class). The image samples are initialized with the buffer pointer and its length. The sample is also passed in a structure (a DIBDATA structure) that holds a number of pieces of information obtained from the CreateDIBSection function.
These samples can then be passed to the draw object. The draw object knows the private format of the samples, and how to get the DIBDATA structure back from them. After the draw object has obtained that information, it can pass a bitmap handle, stored in the DIBDATA structure, down into GDI when it draws the image that the sample contains. By using the bitmap handle from the sample in the drawing, rather than just the buffer pointer (which is the alternative if the sample is not a CImageSample), it gets a modest performance improvement.
See Also