QuickTime 3 Reference

Previous | Chapter Top | Chapter Contents | Next

Field descriptions

frameTime

Contains a pointer to an ICMFrameTime structure The Frame Time Structure . This structure contains a frame's time information for scheduled asynchronous decompression operations.

matrixFlags

Flags specifying information about the transformation matrix. Currently, can be 0 or one of the following:

enum {     matrixFlagScale2x = 1L<<7,     matrixFlagScale1x = 1L<<6,     matrixFlagScaleHalf = 1L<<5 };

matrixType

Contains the type of the transformation matrix, as returned by GetMatrixType(). (For additional information refer to Inside Macintosh: QuickTime, p. 2-342).

dstRect

The destination rectangle. The result of the source rectangle ( srcRect ) transformed by the transformation matrix ( matrix ).

majorSourceChangeSeed

Contains an integer value that is incremented each time a data source is added or removed. This provides a fast way for a codec to know when it needs to redetermine which data source inputs are available.

minorSourceChangeSeed

Contains an integer value that is incremented each time a data source is added or removed, or the data contained in any of the data sources changes. This provides a way for a codec to know if the data available to it has changed.

sourceData

Contains a pointer to a CDSequenceDataSource structure The Decompression Data Source Structure . This structure contains a linked list of all data sources. Because each data source contains a link to the next data source, a codec can access all data sources from this field.

maskRegion

If the maskRegion field is not nil , it contains a QuickDraw region that is equivalent to the bit map contained in the maskBits field. For some codecs, using the QuickDraw region may be more convenient than the mask bit map.

wantedDestinationPixelTypes

Filled in by the codec during ImageCodecPreDecompress . Contains a handle to a zero-terminated list of non-RGB pixels that the codec can decompress to. Leave set to nil if the codec does not support non-RGB pixel spaces. The ICM copies this data structure, so it is up to the codec to dispose of it later. Since the predecompress call can be called often, it is suggested that codecs allocate this handle during the Open routine and dispose of it during the Close routine.

screenFloodMethod

For codecs that require key-color flooding. One of:

enum {     kScreenFloodMethodNone = 0,     kScreenFloodMethodKeyColor = 1,     kScreenFloodMethodAlpha = 2 };

screenFloodValue

If screenFloodMethod is kScreenFloodMethodKeyColor , contains the index of the color that should be used to flood the image area on screen when a refresh occurs. This is valid for both indexed and direct screen devices (e.g., for devices with 16-bit depth, it should contain the 5-5-5 RGB value). If screenFloodMethod is kScreenFloodMethodAlpha , contains the value that the alpha-channel should be flooded with.

preferredOffscreenPixelSize

Should be filled in ImageCodecPreDecompress with the preferred depth of an offscreen buffer should the ICM have to create one. It is not guaranteed that an offscreen buffer will actually be of this depth. A codec should still be sure to specify what depths it can decompress to by using the capabilities field. A codec might use this field if if was capable of decompressing to several depths, but was faster decompressing to a particular depth.

enableBlackLining

If true, indicates that the client has requested blacklining (displaying every other line of the image). Blacklining increases the speed of movie playback while decreasing the image quality.

requestedBufferWidth

Specifies the the width of the image buffer to use, in pixels. For this value to be used, the codecWantsSpecialScaling flag in the CodecCapabilities record must be set.

requestedBufferHeight

Specifies the the height of the image buffer to use, in pixels. For this value to be used, the codecWantsSpecialScaling flag in the CodecCapabilities record must be set.

codecConditions flags

Several new flags exist that can be set in the codecConditions parameter. They are:

enum {
    codecConditionFirstScreen       = 1L << 12,
    codecConditionDoCursor          = 1L << 13,
    codecConditionCatchUpDiff       = 1L << 14,
    codecConditionMaskMayBeChanged  = 1L << 15,
    codecConditionToBuffer          = 1L << 16
};


codecConditionFirstScreen

Indicates when the codec is decompressing an image to the first of multiple screens. That is, if the decompressed image crosses multiple screens, then the codec can look at this flag to determine if this is the first time an image is being decompressed for each of the screens to which it is being decompressed.

A codec that depends on the maskBits field of decompressParams being a valid regionHandle on CDPreDecompress needs to know that in this case it is not able to clip images since the region handle is only passed for the first of the screens; clipping would be incorrect for the subsequent screen for that image.

codecConditionDoCursor

Set to 1 if the decompressor component should shield and unshield the cursor for the current decompression operation. This flag should be set only if the codec has indicated its ability to handle cursor shielding by setting the codecCanShieldCursor flag in the capabilities field during CDPreDecompress .

codecConditionCatchUpDiff

Indicates if the current frame is a "catch up" frame. Set this flag to 1 if the current frame is a catch-up frame. Note that you must also set the codecFlagCatchUpDiff flag to 1. This may be useful to decompressors that can drop frames when playback is falling behind.

codecConditionMaskMayBeChanged

The Image Compression Manager has always included support for decompressors that could provide a bit mask of pixels that were actually drawn when a particular frame was decompressed. If a decompressor can provide a bit mask of pixels that changed, the Image Compression Manager transfers to the screen only the pixels that actually changed.

QuickTime 2.1 extended this capability by adding a new condition flag ( codecConditionMaskMayBeChanged ) to the conditionFlags field of the decompression parameters structure. The decompressor should write back the mask only if this flag is set. This flag is used only by the function ImageCodecBandDecompress .

codecConditionToBuffer

Set to 1 if the current decompression operation is decompressing into an offscreen buffer.