Bitmaps

When Windows calls the Enable function the first time, a graphics driver should initialize the members of the GDIINFO structure that contain information about the device's bitmap technology and capabilities. The following table identifies these members and their purpose:

GDIINFO member Purpose
dpTechnology Specifies the device technology (vector, raster, metafile, and so on).
dpHorzRes Specifies the horizontal resolution of the device.
dpVertRes Specifies the vertical resolution of the device.
dpBitsPixel Specifies the number of adjacent bits required to define a single pixel.
dpPlanes Specifies the number of planes required to define a single pixel.
dpRaster Specifies the raster capabilities (if any) of the device.
dpAspectX Specifies the width of a device pixel.
dpAspectY Specifies the height of a device pixel.
dpAspectXY Specifies the diagonal width of a device pixel.
dpCaps1 Specifies additional raster capabilities.

If the device is a raster printer or a video display, it must set the appropriate GDIINFO members and support the following bitmap functions: BitBlt, BitmapBits, CreateDIBitmap, Pixel, SaveScreenBitmap, SelectBitmap, SetDIBitsToDevice, StretchBlt, StretchDIBits, and ScanLR. In addition, if the device provides device bitmaps, it must support the DeviceBitmap and DeviceBitmapBits functions.

The BitBlt function transfers bits of color data that correspond to a rectangle of pixels on the display from one location in video memory to another location in video memory (the new location corresponds to a second rectangle of pixels). This function is one of the most frequently called display-driver functions and is typically handled by hardware accelerators. The BitmapBits function has multiple purposes, GDI calls it to set bits on a device, to copy bits from a device to a buffer, and to copy bits from a buffer to a device. The three device-independent bitmap (DIB) functions, CreateDIBitmap, SetDIBitsToDevice, and StretchDIBits, perform common operations on DIBs. If a device supports DIBs, it should set the RC_DI_BITMAP value for the dpRaster member of the GDIINFO structure and support each of these functions. The Pixel function sets or retrieves the color of a single pixel with the specified coordinates. The SaveScreenBitmap function is called frequently to save parts of the screen that have been covered by a menu, a dialog box, or some other control or window. The SelectBitmap function is called when an application selects a bitmap into its device context. The StretchBlt function is called to compress or expand the color data for a bitmap that is being copied from one location to another. If a device supports device-dependent bitmaps, it should set the RC_DI_BITMAP value for the dpRaster member of the GDIINFO structure and support the two device-dependent bitmap functions: DeviceBitmap and DeviceBitmapBits.

See Also

Enable, GDIINFO, BitBlt, BitmapBits, BITMAPINFO, BITMAPINFOHEADER, CreateDIBitmap, DeviceBitmap, DeviceBitmapBits, Pixel, SaveScreenBitmap, SelectBitmap, SetDIBitsToDevice, StretchBlt, StretchDIBits, ScanLR