From: Eero Saynatkari <ruby-ml@...>
Date: 2005-12-13T17:08:20+09:00
Subject: Re: Accessing C structures in Ruby

On 2005.12.13 16:42, Joe Van Dyk <joevandyk@gmail.com> wrote:
> On 12/12/05, Eero Saynatkari <ruby-ml@magical-cat.org> wrote:
> > On 2005.12.13 14:14, Joe Van Dyk <joevandyk@gmail.com> wrote:
> > > On 12/12/05, Joe Van Dyk <joevandyk@gmail.com> wrote:
> > > > On 12/12/05, Eero Saynatkari <ruby-forum-reg@mailinator.com> wrote:
> > > > > Joe Van Dyk wrote:
> > > > > > (I've already looked at Swig, btw.  I'd like to do this one by hand.)
> > > > > >
> > > > > > I have the following:
> > > > > >
> > > > > > typedef struct {
> > > > > >   double x;
> > > > > >   double y;
> > > > > >   double z;
> > > > > > } VelocityRecord;
> > > > > >
> > > > > > typedef struct {
> > > > > >   double x;
> > > > > >   double y;
> > > > > >   double z;
> > > > > > } PositionRecord;
> > > > > >
> > > > > > typedef struct {
> > > > > >   int id;
> > > > > >   int type;
> > > > > >   PositionRecord position;
> > > > > >   VelocityRecord velocity;
> > > > > > } Player;
> > > > > >
> > > > > > Player Players[10];
> > > > > >
> > > > > >
> > > > > > The number of Players is fixed ahead of time.  I want to be able to
> > > > > > access that data from Ruby.  Ideally, something like:
> > > > > >
> > > > > > module Simulation
> > > > > >     attr_accessor :players  # Other stuff will be here
> > > > > >     class Player
> > > > > >         class VelocityRecord
> > > > > >             attr_accessor :x, :y :z
> > > > > >         end
> > > > > >         class PositionRecord
> > > > > >           attr_accessor :x, :y, :z
> > > > > >         end
> > > > > >     end
> > > > > > end
> > > > >
> > > > > My typical recommendation is to just wrap a pointer to
> > > > > the struct and pass that around. Then, for each method
> > > > > just extract the pointer, access the correct field and
> > > > > generate a VALUE out of that (inside the function that
> > > > > corresponds to the method).
> > > >
> > > > Can you share more details?  Is that essentially what I've done in my
> > > > later posts on this?
> > >
> > > Here's what I have so far.  Seems to work well:
> > >
> > > #include "ruby.h"
> > > #include "simulation.h"
> > >
> > > VALUE get_frame_count(VALUE self) { return INT2NUM(HIFEN2_Count); }
> > > VALUE get_mission_time(VALUE self) { return INT2NUM(HIFEN2_Mission); }
> > > VALUE get_max_players(VALUE self) { return INT2NUM(MAX_PLAYERS); }
> > >
> > > VALUE player_new(VALUE self, VALUE rb_i)
> > > {
> > >   int i = NUM2INT(rb_i);
> > >   return Data_Wrap_Struct(self, NULL, NULL, &Players[i]);
> > > }
> > >
> > > Player* get_player(VALUE self)
> > > {
> > >   Player *p;
> > >   Data_Get_Struct(self, Player, p);
> > >   return p;
> > > }
> > >
> > > VALUE get_player_id(VALUE self) { return INT2NUM(get_player(self)->id); }
> > >
> > > VALUE get_player_x_pos(VALUE self) { return
> > > rb_float_new(get_player(self)->position.x); }
> > > VALUE get_player_y_pos(VALUE self) { return
> > > rb_float_new(get_player(self)->position.y); }
> > > VALUE get_player_z_pos(VALUE self) { return
> > > rb_float_new(get_player(self)->position.z); }
> > >
> > > VALUE get_player_x_vel(VALUE self) { return
> > > rb_float_new(get_player(self)->velocity.x); }
> > > VALUE get_player_y_vel(VALUE self) { return
> > > rb_float_new(get_player(self)->velocity.y); }
> > > VALUE get_player_z_vel(VALUE self) { return
> > > rb_float_new(get_player(self)->velocity.z); }
> > >
> > > VALUE cSimulation;
> > > VALUE cPlayer;
> > >
> > > void Init_Sim()
> > > {
> > >   cSimulation = rb_define_class("Simulation", rb_cObject);
> > >   rb_define_method(cSimulation, "frame_count", get_frame_count, 0);
> > >   rb_define_method(cSimulation, "mission_time", get_mission_time, 0);
> > >   rb_define_method(cSimulation, "max_players", get_max_players, 0);
> > >
> > >   cPlayer = rb_define_class("Player", rb_cObject);
> > >   rb_define_singleton_method(cPlayer, "new", player_new, 1);
> > >   rb_define_method(cPlayer, "player_id", get_player_id, 0);
> > >
> > >   rb_define_method(cPlayer, "x_position", get_player_x_pos, 0);
> > >   rb_define_method(cPlayer, "y_position", get_player_y_pos, 0);
> > >   rb_define_method(cPlayer, "z_position", get_player_z_pos, 0);
> > >
> > >   rb_define_method(cPlayer, "x_velocity", get_player_x_vel, 0);
> > >   rb_define_method(cPlayer, "y_velocity", get_player_y_vel, 0);
> > >   rb_define_method(cPlayer, "z_velocity", get_player_z_vel, 0);
> > > }
> >
> > Yep, that looks fine to me. There are certainly other ways but aside
> > from some repetitiveness, this is easy and versatile (particularly if
> > you need to pass data to C libraries as well). If you have lots and
> > lots of functions like that, you could even do with a little #define.
> 
> How does my code differ from what you described?

It does not :) There are just many ways you could achieve the same
result --of which I consider this the best merely because of the
simplicity.


E