Re: about luaffi

[Martin Krpan <wtxnh-lua@...>]

On Thu, Sep 13, 2012 at 07:08:32PM -0400, James McKaskill wrote:
> On Thu, Sep 13, 2012 at 6:57 PM, Martin Krpan <wtxnh-lua@yahoo.com.au> wrote:
> > How can I pass table (for example) to my Lua callback function?
> 
> You need to create a struct e.g. ffi.new('struct {int x; int y;}',
> {x=2, y=3}). Otherwise the ffi has no idea how to marshal it. I must
> admit the error could be better. It's actually erroring on a different
> problem that comes up when you try and set a pointer directly to a
> table, the ffi struct will be immediately gc'd.
> 
> > And how do I dereference void* pointer back to lua table in callback function?
> 
> You cast back to a ffi struct and then manually unpack.

That works for table as mentioned above. I guess if table contains
another table, or function, or even some userdata such conversion is not
possible? Anyway I recalled that I can pass any data to callback
function with an upvalue or global variable, so this is not big deal.

I got another error when I tried to use SDL_ttf library.
There is a function with this signature:
SDL_Surface * TTF_RenderUTF8_Solid(TTF_Font *font, const char *text, SDL_Color fg);
typedef struct SDL_Color {
 Uint8 r;
 Uint8 g;
 Uint8 b;
 Uint8 unused;
} SDL_Color;

When I call that function this error shows:

lua: ttt.lua:24: NYI: call arg type
stack traceback:
        [C]: ?
        ttt.lua:24: in main chunk
        [C]: ?

Example script run fine with luajit2. I guess that there is not much
that can be done as it seems that something is Not Yet Implemented.

Bye
Martin

*** ttt.lua ***
local ffi = require 'ffi'
if jit then    NULL = nil else    NULL = ffi.C.NULL end
local sdl = require 'inc/sdl'
local SDL = sdl.SDL
local TTF = sdl.TTF

SDL.SDL_Init(SDL.SDL_INIT_EVERYTHING);
local screen = SDL.SDL_SetVideoMode(320,
                                    240,
                                    16,
                                    SDL.SDL_SWSURFACE);
TTF.TTF_Init()
local fn_name = 'fonts/comic.ttf'
local font = TTF.TTF_OpenFont(fn_name, 32)
if (font == NULL) then
    print('Loading font error:', ffi.string(SDL.SDL_GetError()))
end
local text = "Hello world!"
local fg = ffi.new('SDL_Color')
fg.r=47
fg.g=140
fg.b=180

pic_a = TTF.TTF_RenderUTF8_Solid(font, text, fg)  -- this is line 24

local event=ffi.new('SDL_Event')
local rect=ffi.new('SDL_Rect')
local format = screen.format
local color = SDL.SDL_MapRGB(format, 57, 22, 28)
SDL.SDL_FillRect(screen, nil,  color)

rect.x=10
rect.y=0
sdl.BlitSurface(pic_a, nil, screen, rect)
SDL.SDL_Flip(screen)
SDL.SDL_Delay(2000)
TTF.TTF_Quit()
SDL.SDL_Quit()
*** end of ttt.lua ***