CROSS-PLATFORM PORTABILITY GUIDELINES FOR GALLIUM3D
= General Considerations =
The frontend and winsys driver support a rather limited number of
platforms. However, the pipe drivers are meant to run in a wide number of
platforms. Hence the pipe drivers, the auxiliary modules, and all public
headers in general, should strictly follow these guidelines to ensure
= Compiler Support =
* Include the util/compiler.h.
* Cast explicitly when converting to integer types of smaller sizes.
* Cast explicitly when converting between float, double and integral types.
* Don't use named struct initializers.
* Don't use variable number of macro arguments. Use static inline functions
instead.
* Don't use C99 features.
= Standard Library =
* Avoid including standard library headers. Most standard library functions are
not available in Windows Kernel Mode. Use the appropriate p_*.h include.
== Memory Allocation ==
* Use MALLOC, CALLOC, FREE instead of the malloc, calloc, free functions.
* Use align_pointer() function defined in u_memory.h for aligning pointers
in a portable way.
== Debugging ==
* Use the functions/macros in p_debug.h.
* Don't include assert.h, call abort, printf, etc.
= Code Style =
== Inherantice in C ==
The main thing we do is mimic inheritance by structure containment.
Here's a silly made-up example:
/* base class */
struct buffer
{
int size;
void (*validate)(struct buffer *buf);
};
/* sub-class of bufffer */
struct texture_buffer
{
struct buffer base; /* the base class, MUST COME FIRST! */
int format;
int width, height;
};
Then, we'll typically have cast-wrapper functions to convert base-class
pointers to sub-class pointers where needed:
static inline struct vertex_buffer *vertex_buffer(struct buffer *buf)
{
return (struct vertex_buffer *) buf;
}
To create/init a sub-classed object:
struct buffer *create_texture_buffer(int w, int h, int format)
{
struct texture_buffer *t = malloc(sizeof(*t));
t->format = format;
t->width = w;
t->height = h;
t->base.size = w * h;
t->base.validate = tex_validate;
return &t->base;
}
Example sub-class method:
void tex_validate(struct buffer *buf)
{
struct texture_buffer *tb = texture_buffer(buf);
assert(tb->format);
assert(tb->width);
assert(tb->height);
}
Note that we typically do not use typedefs to make "class names"; we use
'struct whatever' everywhere.
Gallium's pipe_context and the subclassed psb_context, etc are prime examples
of this. There's also many examples in Mesa and the Mesa state tracker.
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