123 lines
4.2 KiB
Markdown
123 lines
4.2 KiB
Markdown
# Developer Documentation
|
|
|
|
Custom functions are internally represented by `struct Sass_C_Function_Descriptor`.
|
|
|
|
## Sass_C_Function_Descriptor
|
|
|
|
```C
|
|
struct Sass_C_Function_Descriptor {
|
|
const char* signature;
|
|
Sass_C_Function function;
|
|
void* cookie;
|
|
};
|
|
```
|
|
|
|
- `signature`: The function declaration, like `foo($bar, $baz:1)`
|
|
- `function`: Reference to the C function callback
|
|
- `cookie`: any pointer you want to attach
|
|
|
|
### signature
|
|
|
|
The signature defines how the function can be invoked. It also declares which arguments are required and which are optional. Required arguments will be enforced by LibSass and a Sass error is thrown in the event a call as missing an argument. Optional arguments only need to be present when you want to overwrite the default value.
|
|
|
|
foo($bar, $baz: 2)
|
|
|
|
In this example, `$bar` is required and will error if not passed. `$baz` is optional and the default value of it is 2. A call like `foo(10)` is therefore equal to `foo(10, 2)`, while `foo()` will produce an error.
|
|
|
|
### function
|
|
|
|
The callback function needs to be of the following form:
|
|
|
|
```C
|
|
union Sass_Value* call_sass_function(
|
|
const union Sass_Value* s_args,
|
|
void* cookie
|
|
) {
|
|
return sass_clone_value(s_args);
|
|
}
|
|
```
|
|
|
|
### cookie
|
|
|
|
The cookie can hold any pointer you want. In the `perl-libsass` implementation it holds the structure with the reference of the actual registered callback into the perl interpreter. Before that call `perl-libsass` will convert all `Sass_Values` to corresponding perl data types (so they can be used natively inside the perl interpretor). The callback can also return a `Sass_Value`. In `perl-libsass` the actual function returns a perl value, which has to be converted before `libsass` can work with it again!
|
|
|
|
## Sass_Values
|
|
|
|
```C
|
|
// allocate memory (copies passed strings)
|
|
union Sass_Value* sass_make_null (void);
|
|
union Sass_Value* sass_make_boolean (bool val);
|
|
union Sass_Value* sass_make_string (const char* val);
|
|
union Sass_Value* sass_make_qstring (const char* val);
|
|
union Sass_Value* sass_make_number (double val, const char* unit);
|
|
union Sass_Value* sass_make_color (double r, double g, double b, double a);
|
|
union Sass_Value* sass_make_list (size_t len, enum Sass_Separator sep, bool is_bracketed);
|
|
union Sass_Value* sass_make_map (size_t len);
|
|
union Sass_Value* sass_make_error (const char* msg);
|
|
union Sass_Value* sass_make_warning (const char* msg);
|
|
|
|
// Make a deep cloned copy of the given sass value
|
|
union Sass_Value* sass_clone_value (const union Sass_Value* val);
|
|
|
|
// deallocate memory (incl. all copied memory)
|
|
void sass_delete_value (const union Sass_Value* val);
|
|
```
|
|
|
|
## Example main.c
|
|
|
|
```C
|
|
#include <stdio.h>
|
|
#include <stdint.h>
|
|
#include "sass/context.h"
|
|
|
|
union Sass_Value* call_fn_foo(const union Sass_Value* s_args, void* cookie)
|
|
{
|
|
// we actually abuse the void* to store an "int"
|
|
return sass_make_number((size_t)cookie, "px");
|
|
}
|
|
|
|
int main( int argc, const char* argv[] )
|
|
{
|
|
|
|
// get the input file from first argument or use default
|
|
const char* input = argc > 1 ? argv[1] : "styles.scss";
|
|
|
|
// create the file context and get all related structs
|
|
struct Sass_File_Context* file_ctx = sass_make_file_context(input);
|
|
struct Sass_Context* ctx = sass_file_context_get_context(file_ctx);
|
|
struct Sass_Options* ctx_opt = sass_context_get_options(ctx);
|
|
|
|
// allocate a custom function caller
|
|
Sass_C_Function_Callback fn_foo =
|
|
sass_make_function("foo()", call_fn_foo, (void*)42);
|
|
|
|
// create list of all custom functions
|
|
Sass_C_Function_List fn_list = sass_make_function_list(1);
|
|
sass_function_set_list_entry(fn_list, 0, fn_foo);
|
|
sass_option_set_c_functions(ctx_opt, fn_list);
|
|
|
|
// context is set up, call the compile step now
|
|
int status = sass_compile_file_context(file_ctx);
|
|
|
|
// print the result or the error to the stdout
|
|
if (status == 0) puts(sass_context_get_output_string(ctx));
|
|
else puts(sass_context_get_error_message(ctx));
|
|
|
|
// release allocated memory
|
|
sass_delete_file_context(file_ctx);
|
|
|
|
// exit status
|
|
return status;
|
|
|
|
}
|
|
```
|
|
|
|
## Compile main.c
|
|
|
|
```bash
|
|
gcc -c main.c -o main.o
|
|
gcc -o sample main.o -lsass
|
|
echo "foo { margin: foo(); }" > foo.scss
|
|
./sample foo.scss => "foo { margin: 42px }"
|
|
```
|