Lua library for accessing the framebuffer of a chumby

example.lua

local screen = require("screen")
print("loaded screen")

img, success = screen.initScreen("/dev/fb0")

if success then
	print("Opened frame buffer")
else
	error("Faild to open frame buffer")
end

c, c2 = screen.colour(img, 255, 0, 255)
print("Set colour: "..c..", "..c2)


screen.background(img)

--screen.colour(img, 255, 0, 0)
--img = screen.pixel(img, 0, 239)
--screen.line(img, 0, 0, 319, 239)
--screen.line(img, 0, 239, 319, 0)

screen.draw(img)

Screen.c

/*
 * A Lua library in C to display interface
 * with the chumby frame buffer
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <errno.h>
#include <math.h>
#include <lua.h>
#include <lauxlib.h>
#include <lualib.h>

#define SCREEN "Screen"
#define SCREENMETA "Screen.meta"
#define FRAMESIZE 320*244*2

typedef struct {
    FILE * fd;
    char framebuffer[FRAMESIZE];
    char colour[2];
}Screen;


// static Screen* checkScreen(lua_State *L, int index);
static void setPixel(int x, int y, Screen *scr);
static Screen* pushScreen(lua_State *L, Screen scr);

int iinit_screen(lua_State *L);
int iset_colour(lua_State *L);
int iset_pixel(lua_State *L);
int iset_background(lua_State *L);
int iset_line(lua_State *L);
int idraw_screen(lua_State *L);
int iclose(lua_State *L);
int luaopen_screen(lua_State *L);

const struct luaL_Reg screenLib[] = {
    {"initScreen", iinit_screen},
    {"colour", iset_colour},
    {"pixel", iset_pixel},
    {"background", iset_background},
    {"draw", idraw_screen},
    {"line", iset_line},
    {NULL, NULL}
};

static Screen* pushScreen(lua_State *L, Screen scr)
{
  Screen *pi = (Screen *)lua_newuserdata(L, sizeof(Screen));
  *pi = scr;
  
  luaL_getmetatable(L, SCREENMETA);
  lua_setmetatable(L, -2);
  
  return pi;
}

static Screen* checkScreen(lua_State *L, int index) {
    void *ud = luaL_checkudata(L, 1, SCREENMETA);
    luaL_argcheck(L, ud != NULL, 1, "`Screen' expected");
    return (Screen*)ud;
}

static void setPixel(int x, int y, Screen *scr) {
    int pos = (((320*y)+x)*2);
    scr->framebuffer[pos] = scr->colour[0];
    scr->framebuffer[pos+1] = scr->colour[1];
}

// create new screen
int iinit_screen(lua_State *L){
    const char *serialport = luaL_checkstring(L, 1);
    
    Screen scr;
    scr.fd = fopen(serialport, "r+b");
    
    pushScreen(L, scr);
    
    int success = 1;
    if (!scr.fd)
        success = 0;
    
    lua_pushboolean(L, success);
    
	return 2;
}

int iset_colour(lua_State *L) {
    Screen *scr = checkScreen(L, 1);
    int r = luaL_checkint(L, 2);
    int g = luaL_checkint(L, 3);
    int b = luaL_checkint(L, 4);
    
    short int colour16 = (short)(((b&0xf8)<<8) + ((r&0xfc)<<3) + ((g&0xf8)>>3));
    
    scr->colour[0] = ((colour16 >> 8) & 0xff);
    scr->colour[1] = ((colour16 >> 0) & 0xff);
    
    lua_pushnumber(L, scr->colour[0]);
    lua_pushnumber(L, scr->colour[1]);
	return 2;
}

int iset_pixel(lua_State *L) {
    Screen *scr = checkScreen(L, 1);
    int x = luaL_checkint(L, 2);
    int y = luaL_checkint(L, 3);
    
    setPixel(x, y, scr);
    
    // pushScreen(L, scr);
    return 0;
}

int iset_background(lua_State *L) {
    Screen *scr = checkScreen(L, 1);
    
    int i;
	for (i=0; i<320; i++) {
		int j;
		for (j=0; j<240; j++) {
    	    setPixel(i, j, scr);
		}
	}
    
    // pushScreen(L, scr);
    return 0;
}

int iset_line(lua_State *L) {
    Screen *scr = checkScreen(L, 1);
    int x0 = luaL_checkint(L, 2);
    int y0 = luaL_checkint(L, 3);
    int x1 = luaL_checkint(L, 4);
    int y1 = luaL_checkint(L, 5);
    
    int dx = abs(x1-x0);
    int dy = abs(y1-y0);
    
    int sx, sy, err;
   
    if (x0 < x1)
       sx = 1;
    else
       sx = -1;
    
    if (y0 < y1)
        sy = 1;
    else
        sy = -1;
    
    while (1) {
        setPixel(x0, y0, scr);
        if ((x0==x1)&&(y0==y1))
            break;
        
        int e2 = 2*err;
        if (e2 > -dy) {
            err = err - dy;
            x0 = x0 + sx;
        }
        if (e2 < dx) {
            err = err + dx;
            y0 = y0 + sy;
        }
    }
    
    // pushScreen(L, scr);
    return 0;
}

int idraw_screen(lua_State *L) {
    Screen *scr = checkScreen(L, 1);
    
    rewind(scr->fd);
    fwrite(scr->framebuffer, 1, FRAMESIZE, scr->fd);
    return 0;
}

int iclose(lua_State *L) {
    Screen *scr = checkScreen(L, 1);
    
    fclose(scr->fd);
    return 0;
}

int luaopen_screen(lua_State *L) {
    luaL_newmetatable(L, SCREENMETA);
    luaL_register(L, "screen", screenLib);
    
    return 1;
}