Inside Macintosh: QuickTime Components /

Chapter 5 - Sequence Grabber Components / Sequence Grabber Components Reference

Sequence Grabber Component Functions / Working With Video Channels

SGSetUseScreenBuffer

The SGSetUseScreenBuffer function allows you to control whether a video channel uses an offscreen buffer.

pascal ComponentResult SGSetUseScreenBuffer (SGChannel c, 
                                       Boolean useScreenBuffer);

c

Identifies the channel for this operation. You provide your
connection identifier. You connect to a channel component by calling the SGNewChannel or SGNewChannelFromComponent function, discussed on page 5-29 and page 5-30, respectively.

useScreenBuffer

Indicates whether to use an offscreen buffer. If you set this parameter to true, the channel draws directly to the screen. If you set it to false, the channel may use an offscreen buffer. If the channel cannot work with offscreen buffers, it ignores this parameter.

DESCRIPTION

By default, video channels try to draw directly to the screen. The SGSetUseScreenBuffer function allows you to direct a video channel to
draw to an offscreen buffer. If the channel cannot draw offscreen, it ignores
this function. Note that you may not call this function when you are recording.

Directing a channel to draw offscreen may be useful if you are performing transformations on the data before displaying it (such as blending it with another graphical image).

RESULT CODES

paramErr	-50	Invalid parameter value
cantDoThatInCurrentMode	-9402	Request invalid in current mode

SEE ALSO

You can determine whether you have allowed a channel to draw offscreen by calling the SGGetUseScreenBuffer function, which is described next.

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