Re: Light User Data and C Data Processing

["varol kaptan" <varol.kaptan@...>]

the luaglut library
(http://lua-users.org/files/wiki_insecure/users/VarolKaptan/) has a
component called memarray which may be used to create pools of raw
memory and view them as uchar, char, int, double, etc. Instead of
creating new memory you can also provide alternative views to an
already allocated memory by providing the starting address as a light
userdata.

Some examples:

varol@thales:~$ lua
Lua 5.0.2  Copyright (C) 1994-2004 Tecgraf, PUC-Rio
> require 'memarray'
> a = memarray('int', 8)
> =a:size(), a:length()
32	8
> for i = 0, a:length()-1 do a[i] = i end
> for i = 0, a:length()-1 do io.write(a[i], ' ') end print()
0 1 2 3 4 5 6 7
> b = memarray('uint', 4, a:ptr(4)) -- just a different view of a, starting from 4'th integer
> for i = 0, b:length()-1 do io.write(b[i], ' ') end print()
4 5 6 7
> =a[4], b[0]
4	4
> a[4] = -1
> =a[4], b[0]
-1	4294967295
>

Varol Kaptan

On 9/26/06, Wesley Smith <wesley.hoke@gmail.com> wrote:
> Hi,
> I'm wanting to use Lua's Light User Data functionality to prototype
> some data processing routines.  I'm basically dealing with a pointer
> to raw memory and a header struct that describes the memory layout.
> It looks something like this in C:
>
> char *memory_in;
> t_mem_header *memory_in_header;
>
> char *memory_out;
> t_mem_header *memory_out_header;
>
> What I want to do is pass all 4 of these pointers to lua in as light
> user data.  Allocation and deallocation of this memory is handled by
> the app.  Typical C usage of this goes as follow:
>
> void process_data(t_mem_header *memory_in_header, char *memory_in,
> t_mem_header *memory_out_header, char *memory_out)
> {
>     /*
>         leaving out stuff like variable declarations
>    */
>
>       for(j=0; j < height; j++) {
>             for(i=0; i < width; i++) {
>                   //process input and put result in output
>               }
>       }
> }
>
>
> Now, the data can be many flavors like uchar, long, float, or double.
> I'd like to use Lua to replace the double for loops such that I can
> load little processing scripts and see how things work and when I get
> something that works well I would then most likely go back to C and
> hard code it.  A secondary motive for doing this is to get to know Lua
> more and just try some ideas out.  I've looked around for some info
> and examples on uses of Light User Data, but I'm still not sure
> exactly where to start.  How do I go about writing Lua functions that
> process the Light User Data such that I can script the processing?
>
> As a simple starter, how would I recreate the following:
>  *(float *)(memory_out + j*width + i) =  1.0 + *(float *)(memory_in+
> j*width + i);
>
> thanks,
> wes