DVM_UPDATE

The DVM_UPDATE message requests a user-mode video capture driver to update the overlay display.

Parameters

dwDriverID

Video channel identifier. For this message, the driver should only accept VIDEO_EXTERNALOUT. (For details, see Opening Video Channels.)

hDriver

Driver handle.

uMsg

DVM_UPDATE

lParam1t

Handle to a client window.

lParam2

Handle to a display device context.

Return Value

The driver should return DV_ERR_OK if the operation succeeds. Otherwise, it should return one of the DV_ERR error codes defined in msvideo.h. Custom error codes are also allowed (see DVM_GETERRORTEXT).

Comments

A client sends the DVM_UPDATE message by calling the driver’s DriverProc entry point, passing the specified parameter values. Applications can send this message by calling the videoUpdate function, which is described in the Video for Windows Development Kit.

If the hardware supports color keying, the driver should repaint the current key color onto the overlay area. If the key color has not yet been specified, the driver should specify it. The driver should create a brush using the key color, convert the screen coordinates describing the overlay area into client coordinates, and repaint the overlay area, as illustrated in the sample drivers.

Typically, a client sends this message whenever its window receives a WM_PAINT, WM_MOVE, WM_POSITIONCHANGED, or WM_SIZE message. It also typically sends the message after sending a DVM_SRC_RECT or DVM_DST_RECT message.

User-mode video capture drivers using VCUser.lib can call the following functions to set or to determine the key color:

VC_GetKeyColour 

VC_SetKeyColourPalIdx 

VC_SetKeyColourRGB