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Note: no + or - switches are available for
these options. They cannot be used from the command line. They may only be
used from INI files.
POV-Ray offers you the opportunity to shell-out to the operating system at several key points to execute another program or batch file. Usually this is used to manage files created by the internal animation loop however the shell commands are available for any scene. The string s is a single line of text which is passed to the operating system to execute a program. For example
Post_Scene_Command=tga2gif -d -m myfile
would use the utility tga2gif with the -D and
-M parameters to convert myfile.tga to
myfile.gif after the scene had finished rendering.
Note: individual platforms may provide means of preventing shell-outs from occurring. For example, the Windows version provides a menu command to turn shell-outs off (which is the default setting for that platform). The reason for this (along with file I/O restrictions) is to attempt to prevent untrusted INI files from doing harm to your system.
It could get cumbersome to change the Post_Scene_Command
every time you changed scene names. POV-Ray can substitute various values
into a command string for you. For example:
Post_Scene_Command=tga2gif -d -m %s
POV-Ray will substitute the %s with the scene name in the
command. The scene name is the Input_File_Name or
+I setting with any drive, directory and extension removed. For
example:
Input_File_Name=c:\povray3\scenes\waycool.pov
is stripped down to the scene name waycool which results
in...
Post_Scene_Command=tga2gif -d -m waycool
In an animation it may be necessary to have the exact output file name
with the frame number included. The string %o will substitute
the output file name. Suppose you want to save your output files in a zip
archive using the utility program pkzip. You could do...
Post_Frame_Command=pkzip -m %s %o
After rendering frame 12 of myscene.pov POV-Ray would shell
to the operating system with
pkzip -m myscene mysce012.tga
The -M switch in pkzip moves
mysce012.tga to myscene.zip and removes it from the
directory. Note that %o includes frame numbers only when in an
animation loop. During the Pre_Scene_Command and
Post_Scene_Command there is no frame number so the original,
unnumbered Output_File_Name is used. Any
User_Abort_Command or Fatal_Error_Command not inside the
loop will similarly give an unnumbered %o substitution.
Here is the complete list of substitutions available for a command string.
%o |
Output file name with extension and embedded frame number if any |
%s |
Scene name derived by stripping path and ext from input name |
%n |
Frame number of this frame |
%k |
Clock value of this frame |
%h |
Height of image in pixels |
%w |
Width of image in pixels |
%% |
A single % sign. |
Here is the sequence of events in an animation loop. Non-animated scenes work the exact same way except there is no loop.
If the user interrupts processing the User_Abort_Command, if
any, is executed. User aborts can only occur during the parsing and rendering
parts of step (4b) above. If a fatal error occurs that POV-Ray notices the
Fatal_Error_Command, if any, is executed. Sometimes an
unforeseen bug or memory error could cause a total crash of the program in
which case there is no chance to shell out. Fatal errors can occur just about
anywhere including during the processing of switches or INI files. If a fatal
error occurs before POV-Ray has read the Fatal_Error_Command
string then obviously no shell can occur.
Note: the entire scene is re-parsed for every frame. Future versions of POV-Ray may allow you to hold over parts of a scene from one frame to the next but for now it starts from scratch every time.
Note: that the Pre_Frame_Command occurs before the
scene is parsed. You might use this to call some custom scene generation utility
before each frame. This utility could rewrite your .pov
or .inc files if needed. Perhaps you will want to generate new
.gif or .tga files for image maps or height fields on each frame.
Note: that no + or - switches are available for
these options. They cannot be used from the command line. They may only be
used from INI files.
Most operating systems allow application programs to return an error code if something goes wrong. When POV-Ray executes a shell command it can make use of this error code returned from the shell process and take some appropriate action if the code is zero or non-zero. POV-Ray itself returns such codes. It returns 0 for success, 1 for fatal error and 2 for user abort.
The actions are designated by a single letter in the different
..._Return=s options. The possible actions are:
I |
ignore the code |
S |
skip one step |
A |
all steps skipped |
Q |
quit POV-Ray immediately |
U |
generate a user abort in POV-Ray |
F |
generate a fatal error in POV-Ray |
For example if your Pre_Frame_Command calls a program which
generates your height field data and that utility fails then it will return a
non-zero code. We would probably want POV-Ray to abort as well. The option
Pre_Frame_Return=F will cause POV-Ray to do a fatal abort if the
Pre_Frame_Command returns a non-zero code.
Sometimes a non-zero code from the external process is a good thing. Suppose
you want to test if a frame has already been rendered. You could use the
S action to skip this frame if the file is already rendered.
Most utilities report an error if the file is not found. For example the
command...
pkzip -V myscene mysce012.tga
tells pkzip you want to view the catalog of myscene.zip for
the file mysce012.tga. If the file isn't in the archive
pkzip returns a non-zero code.
However we want to skip if the file is found. Therefore we need to reverse
the action so it skips on zero and doesn't skip on non-zero. To reverse
the zero vs. non-zero triggering of an action precede it with a
"-" sign (note a "!" will also
work since it is used in many programming languages as a negate
operator).
Pre_Frame_Return=S will skip if the code shows error
(non-zero) and will proceed normally on no error (zero).
Pre_Frame_Return=-S will skip if there is no error (zero) and will
proceed normally if there is an error (non-zero).
The default for all shells is I which means that the return
action is ignored no matter what. POV-Ray simply proceeds with whatever it
was doing before the shell command. The other actions depend upon the
context. You may want to refer back to the animation loop sequence chart in
the previous section "Shell Command Sequencing". The action for
each shell is as follows.
On return from any User_Abort_Command if there is an action triggered...
| ...and you have specified... | ...then POV-Ray will.. |
F |
Then turn this user abort into a fatal error. Do the
Fatal_Error_Command, if any. Exit POV-Ray with error code 1. |
S, A, Q, or U |
Then proceed with the user abort. Exit POV-Ray with error code 2. |
On return from any Fatal_Error_Command then POV-Ray will
proceed with the fatal error no matter what. It will exit POV-Ray with error
code 1.
On return from any Pre_Scene_Command,
Pre_Frame_Command, Post_Frame_Command or
Post_Scene_Commands if there is an action triggered...
| ...and you have specified... | ...then POV-Ray will... |
F |
...turn this user abort into a fatal error. Do the
Fatal_Error_Command, if any. Exit POV-Ray with error code 1. |
U |
...generate a user abort. Do the User_Abort_Command, if
any. Exit POV-Ray with an error code 2. |
Q |
..quit POV-Ray immediately. Acts as though POV-Ray never really ran. Do
no further shells, (not even a Post_Scene_Command) and exit
POV-Ray with an error code 0. |
On return from a Pre_Scene_Command if there is an action
triggered...
| ...and you have specified... | ...then POV-Ray will... |
S |
...skip rendering all frames. Acts as though the scene completed all
frames normally. Do not do any Pre_Frame_Command or
Post_Frame_Commands. Do the Post_Scene_Command, if
any. Exit POV-Ray with error code 0. On the earlier chart this means skip
step #4. |
A |
...skip all scene activity. Works exactly like Q quit. On
the earlier chart this means skip to step #6. Acts as though POV-Ray never
really ran. Do no further shells, (not even a
Post_Scene_Command) and exit POV-Ray with an error code 0. |
On return from a Pre_Frame_Command if there is an action
triggered...
| ...and you have specified... | ...then POV-Ray will... |
S |
...skip only this frame. Acts as though this frame never existed. Do
not do the Post_Frame_Command. Proceed with the next frame. On
the earlier chart this means skip steps (4b) and (4c) but loop back as
needed in (4d). |
A |
...skip rendering this frame and all remaining frames. Acts as though
the scene completed all frames normally. Do not do any further
Post_Frame_Commands. Do the Post_Scene_Command, if any.
Exit POV-Ray with error code 0. On the earlier chart this means skip the
rest of step (4) and proceed at step (5). |
On return from a Post_Frame_Command if there is an action
triggered...
| ...and you have specified... | ...then POV-Ray will... |
S or A |
...skip all remaining frames. Acts as though the scene completed all
frames normally. Do not do any further Post_Frame_Commands.
Do the Post_Scene_Command, if any. Exit POV-Ray with error
code 0. On the earlier chart this means skip the rest of step (4) and
proceed at step (5). |
On return from any Post_Scene_Command if there is an action
triggered and you have specified S or A then no
special action occurs. This is the same as I for this shell
command.
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