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You may open, read, write, append, and close plain ASCII text files while parsing POV-Ray scenes. This feature is primarily intended to help pass information between frames of an animation. Values such as an object's position can be written while parsing the current frame and read back during the next frame. Clever use of this feature could allow a POV-Ray scene to generate its own include files or write self-modifying scripts. We trust that users will come up with other interesting uses for this feature.
Note: some platform versions of POV-Ray (e.g. Windows) provide means to restrict the ability of scene files to read & write files.
Users may open a text file using the #fopen
directive. The
syntax is as follows:
FOPEN_DIRECTIVE: #fopen IDENTIFIER "filename" OPEN_TYPE OPEN_TYPE: read | write | append
Where IDENTIFIER is an undefined identifier used to reference
this file as a file handle, "filename" is any string
literal or string expression which specifies the file name. Files opened with
the read
are open for read only. Those opened with
write
create a new file with the specified name and it overwrites any
existing file with that name. Those opened with append
opens a
file for writing but appends the text to the end of any existing file.
The file handle identifier created by #fopen
is always global
and remains in effect (and the file remains open) until the scene parsing is
complete or until you #fclose
the file. You may use
#ifdef
FILE_HANDLE_IDENTIFIER to see if a file is open.
Files opened with the #fopen
directive are automatically
closed when scene parsing completes however you may close a file using the
#fclose
directive. The syntax is as follows:
FCLOSE_DIRECTIVE: #fclose FILE_HANDLE_IDENTIFIER
Where FILE_HANDLE_IDENTIFIER is previously opened file opened
with the #fopen
directive. See
"The #fopen Directive".
You may read string, float or vector values from a plain ASCII text file directly into POV-Ray variables using the #read directive. The file must first be opened in "read" mode using the #fopen directive. The syntax for #read is as follows:
READ_DIRECTIVE: #read FILE_HANDLE_IDENTIFIER, DATA_IDENTIFIER[,DATA_IDENTIFIER]..) DATA_IDENTIFIER: UNDECLARED_IDENTIFIER | FLOAT_IDENTIFIER | VECTOR_IDENTIFIER | STRING_IDENTIFIER
Where FILE_HANDLE_IDENTIFIER is the previously opened file. It is followed by one or more DATA_IDENTIFIERs separated by commas. The parentheses around the identifier list are required. A DATA_IDENTIFIER is any undeclared identifier or any previously declared string identifier, float identifier, or vector identifier. Undefined identifiers will be turned into global identifiers of the type determined by the data which is read. Previously defined identifiers remain at whatever global/local status they had when originally created. Type checking is performed to insure that the proper type data is read into these identifiers.
The format of the data to be read must be a series of valid string literals, float literals, or vector literals separated by commas. Expressions or identifiers are not permitted in the data file however unary minus signs and exponential notation are permitted on float values.
If you attempt to read past end-of-file, the file is automatically closed
and the FILE_HANDLE_IDENTIFIER is deleted from the symbol table.
This means that the boolean function
defined(
IDENTIFIER)
can be used to detect
end-of-file. For example:
#fopen MyFile "mydata.txt" read #while (defined(MyFile)) #read (MyFile,Var1,Var2,Var3) ... #end
You may write string, float or vector values to a plain ASCII text file
from POV-Ray variables using the #write
directive. The file must
first be opened in either write
or append
mode
using the #fopen
directive. The syntax for #write
is as follows:
WRITE_DIRECTIVE: #write( FILE_HANDLE_IDENTIFIER, DATA_ITEM[,DATA_ITEM]...) DATA_ITEM: FLOAT | VECTOR | STRING
Where FILE_HANDLE_IDENTIFIER is the previously opened file. It is
followed by one or more DATA_ITEMs separated by commas. The
parentheses around the identifier list are required. A DATA_ITEM is
any valid string expression, float expression, or vector expression. Float
expressions are evaluated and written as signed float literals. If you
require format control, you should use the str(VALUE,L,P)
function to convert it to a formatted string. See "String Functions"
for details on the str
function. Vector expressions are
evaluated into three signed float constants and are written with angle
brackets and commas in standard POV-Ray vector notation. String expressions
are evaluated and written as specified.
Note: data read by the #read
directive must have comma
delimiters between values and quotes around string data but the
#write
directive does not automatically output commas or quotes.
For example the following #read
directive reads a string, float and
vector.
#read (MyFile,MyString,MyFloat,MyVect)
It expects to read something like:
"A quote delimeted string", -123.45, <1,2,-3>
The POV-Ray code to write this might be:
#declare Val1 = -123.45; #declare Vect1 = <1,2,-3>; #write(MyFile,"\"A quote delimited string\",",Val1,",",Vect1,"\n")
See "String Literals" and "Text Formatting" for details on writing special characters such as quotes, newline, etc.
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