On Feb 13, 2010, at 8:43 PM, Matt Gushee wrote:
> * I think I need to start by calling FT_Init_FreeType, right? Well,
> that has a stack effect of ( library -- FT_Error ). What I don't
> get is, where does the 'library' argument come from? I tried
When calling a C function, the arguments in Factor map directly to the
arguments in C. Looking at the FreeType docs at
http://freetype.sourceforge.net/freetype2/docs/reference/ft2-toc.html, the
"library" argument is an out parameter that points to an FT_Library (itself a
pointer type) that gets filled with the library handle. You can use <void*> to
allocate a byte array large enough to receive the value, then *void* to
interpret it into an "alien" object (the Factor representation of a pointer).
Something like this:
SYMBOL: freetype-library
f <void*> [ FT_Init_FreeType drop ] keep *void*
freetype-library set
(I'm dropping the error code return value, but in real code, you would want to
check it and throw a Factor error on failure there.) You can then use that
value as the "library" parameter to other FreeType calls. There are <type> and
*type words for all the basic C types that you can use to handle other out
pointer parameters like this. For parameters of primitive value types, Factor
handles the conversion for you. "char*" typed parameters convert between Factor
strings and UTF-8 encoded C strings. Structs and struct pointers and handled
with "struct" objects on the Factor side, which behave similarly to Factor
tuples. So you could call FT_New_Face (which takes a library, a pathname, and a
face index, and an FT_Face output parameter) like this:
freetype-library get
"/path/to/font.ttf" 0 f <void*> [ FT_New_Face drop ] *void*
Again, you should type «"alien" help» in the listener for full documentation on
the C FFI.
-Joe
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