ref_vfmethod_paramProc - shekh/VirtualDub2 GitHub Wiki

VirtualDub Plugin SDK 1.2

paramProc video filter method

paramProc

Initializes a filter's per-instance data.

long paramProc(VDXFilterActivation *fa, const VDXFilterFunctions *ff);

Parameters

fa	Pointer to filter activation structure.
ff	Pointer to callback function structure.

Thread safety

This method is not thread-safe.

Exceptions

This function must not throw exceptions (see Except()).

Return value

A bitfield indicating filter behavior:

FILTERPARAM_SWAP_BUFFERS
The input and output buffers must be distinct. If this flag is absent, they overlap (in-place mode).

FILTERPARAM_NEEDS_LAST
V1-V15 only: Enables a third buffer containing the previous input frame to the filter. This flag is prohibited in V16+.

FILTERPARAM_HAS_LAG(count)
V7+ only: Indicates that the filter's output lags behind its input by the specified number of frames.

FILTERPARAM_SUPPORTS_ALTFORMATS
V12+ only: The filter supports formats other than 32-bit RGB. This flag is required starting with V16.

FILTERPARAM_NOT_SUPPORTED
V12+ only: The filter does not support the given input format. Note that this flag should not be combined with any other values, as it sets all bits.

FILTERPARAM_ALIGN_SCANLINES
V14+ only: All source and output scanlines are guaranteed to be aligned to 16-byte boundaries and to be readable/writable to the next 16-byte boundary. This is useful for fast SSE optimized routines.

FILTERPARAM_PURE_TRANSFORM
V14+ only: The filter has no side effects and produces output that is solely dependent upon the source frame data and configuration parameters. In particular, running the filter on the same source frames will produce the same output, even if the filter is run multiple times to produce the same output frame, and even if the output frame numbers are different. This allows the host to deduce when two output frames would be the same and optimize the output appropriately.

Default behavior

If omitted, a return value of FILTERPARAM_SWAP_BUFFERS is assumed.

Remarks

paramProc can be called relatively frequently when the user is arranging filter order, so it should not take a long time to execute. The function should also be robust to improper frame sizes, such as 1x2 bitmaps -- frame size validation should be handled in startProc instead.

	Be careful when setting `fa->dst.offset`. In a two-buffer filter, the destination buffer offset should be set to zero, unless the filter creates a larger image and returns a subrectangle of it. However, in an in-place filter, the destination offset must be at least as much as the source offset, and if the destination image is the same size, it must be exactly the same. Setting it to zero in an in-place filter can result in x1/y2 cropping not working correctly in VirtualDub's filter chain.

V12+ only: Setting the depth field of the destination bitmap to zero activates the mpPixmapLayout field and allows formats other than 32-bit RGB.

V12+ only: Setting the mpPixmapLayout->pitch field to zero tells the host to compute appropriate pitch and offset parameters. In this case, only the width, height, and format fields are used.