TYPE: COP
TITLE: Z Comp COP

This operation does a Z composite of 2 images. At least 1 image should have
a depth or point plane containing depth information.

This operation is implemented in VEX. Right click on the dialog '?' help for 
more help on VEX. 

Parameters
    Foreground Offset - Allows you to specify an offset Z-depth, as well as
                        an XY offset for the foreground image (X,Y,Z)

    Use Depth Plane For Background - The background will use a depth or point
				     plane if on.  If off, specify the global
				     depth of the image with the Background
				     Depth parameter. 
    Background Depth  - The global background depth.

    Use Depth Plane For Foreground - The foreground will use a depth or point
				     plane if on.  If off, specify the global
				     depth of the image with the Foreground
				     Depth parameter. 
    Foreground Depth  - The global foreground depth.

    Depth/Point Plane - The name of the depth or point plane to use.
    Supersample       - The amount of aliasing to do. '2' means 2x2.

Mask & Plane Scope, Frame Scope page:
    Overview - See extra help (Middle click on the dialog '?' help).

Local Variables:
    L   - Sequence length
    S   - Start of sequence
    E   - End of sequence
    IL  - Input sequence length
    SR  - Sequence frame rate
    NP  - Number of planes in sequence
    W,H - Width and height of image
    I   - Image index (0 at start frame)
    IT  - Image time (0 at start frame)
    AI  - Current plane array index
    PI  - Current plane index
    PC  - Num of channels in current plane
