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Chapter 3 - Image Compression Manager / Image Compression Manager Reference

Image Compression Manager Functions / Changing Sequence-Decompression Parameters

GetDSequenceScreenBuffer

The GetDSequenceScreenBuffer function enables you to determine the location of the offscreen buffer allocated by the decompressor.

pascal OSErr GetDSequenceScreenBuffer (ImageSequence seqID,
                                        GWorldPtr *gworld);

seqID

Contains the unique sequence identifier that was returned by the DecompressSequenceBegin function (described on page 3-107).

gworld

Contains a pointer to a field to receive a pointer to the graphics world structure (defined by the GWorld data type) describing the graphics world for the screen buffer. If the decompressor has allocated an offscreen buffer, the decompressor returns an appropriate GWorldPtr in the field referred to by this parameter. If the decompressor has not allocated a buffer, the function returns an error result code.

You should not dispose of this graphics world--the returned pointer refers to a buffer that the Image Compression Manager is using. It is disposed of for you when the CDSequenceEnd function is called. For details on CDSequenceEnd, see page 3-113.

DESCRIPTION

The decompressor uses this buffer for decompressed images. During decompression the decompressor writes the decompressed image to an offscreen buffer and then copies the results to the screen. This reduces the tearing effect that can result from decompressing directly to the screen. You cause the decompressor to use a screen buffer by setting the codecFlagUseScreenBuffer flag to 1 in the flags parameter to the DecompressSequenceBegin function.

RESULT CODES

noErr	0	No error
paramErr	-50	Invalid parameter specified

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