Questions about running renders with RenderMan in ShadeTree.

    This is a problem with your prman environment.

    Make sure your $RMANTREE and $PATH variables are pointing at
    the correct version of renderman.

    Also, make sure you are running the correct version of shadetree
    for renderman. ie:

        Version      Stree Command Line
	-------      ------------------
	PRMAN 3.5    st -prman3.5
	PRMAN 3.6    st -prman3.6
	PRMAN 3.5    st -prman3.7

    If you don't want to specify the command line flags all the time,
    try setting your STREE_LIB variable; then you can just type 'st'
    to get the correct version.

    You are probably running low on ram. Run 'gr_osview -a' to see what's
    going on with ram, or if your machine is swapping.

    Try changing your render paramemters. 

	> Lower your output resolution in the Render Options Editor

	> Use Zoom to zoom away from the object (decreases tesselation size)

	> Decrease your sampling rate

    Even rendering a single sphere primitive can throw a machine into swap 
    if your shader is complicated enough, or your render parameters are
    set wastefully.

    See the animation example stree files that end in *_anim.stree.

    To render a frame you need at least two things:

	> Set the Start/End/Increment in the Render Options Editor

	> You should have an argument called 'frame' in the Argument Editor

    As a convenience, the Globals->FrameRange box can be used to 
    easily access the frame range values. 

    See the animation examples, ie. all example stree files that 
    end in _anim.

    In the Render Options Editor, there are options at the very bottom
    to let you set a frame range, below the prompt for the custom render
    script.

    These frame ranges are passed to all render scripts as environment
    variables:

	STREE_SFRM	- start frame
	STREE_EFRM	- end frame
	STREE_IFRM	- frame increment

    An example of a custom render script that uses these variables
    is shown in:

	/usr/local/shadetree/prman/bin/custom-render-animate

    See the CUSTOM RENDER SCRIPTS section in 'man shadetree-custom'
    for more information.

    Questions regarding writing shaders in RenderMan with ShadeTree.

    Prman 3.5 
	This is the first version supported by ShadeTree. 
	We support the entire language, EXCEPT:

	    > uniform and varying

    Prman 3.6
	These new features in 3.6:

	    > spheres are now primitives, not bicubic approximations

	These new features in 3.6 are NOT supported by ShadeTree prman-3.6

	    > shadow() bias parameter
	    > vertex class introduced
	    > vector, normal and hpoint

    Prman 3.7
	These new 3.7 features ARE SUPPORTED in ShadeTree:

	    > Arrays
	    > New data types (string, vector, normal, matrix)
	    > nshader compiler
	    > New variables __nondiffuse and __nonspecular
	    > Local variable declarations
	    > Time derivatives (dtime, dPdtime)
	    > Message passing
	    > These new functions:

		vtransform()   ntransform()   determinant()
		ptlined()      filterstep()   specularbrdf()
		min()          max()          clamp()
		concat()       format()       match()

	These can be controlled via the custom render script:

	    > Curve primitives
	    > Level of detail (RiDetail)
	    > Procedural primitives

	These new 3.7 features are NOT SUPPORTED in ShadeTree currently:

	    > Local functions (functions declared in functions)
	    > output and extern declarations

    In RenderMan, this is almost always due to Displacement Bounds being
    'off' or set too low. It usually shows as strange 'clipping' artifacts:
    sharp edged holes in the object.
    
    It is best to keep Displacement Bounds 'off' unless you find you need 
    it, as the function can drastically impact render time.  To enable the
    function, open the Render Options Editor, and set the 'Displace Bounds'
    to a value appropriate for your displacement.  
    
    For details, see the 'Displace Bounds' help button in the
    'Render->Render Options Editor' from the main menu.