gifenc.c

#include "gifenc.h"

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#ifdef _WIN32
#include <io.h>
#else
#include <unistd.h>
#endif

#pragma warning(disable : 4996)

/* helper to write a little-endian 16-bit number portably */
#define write_num(fd, n) write((fd), (uint8_t []) {(n) & 0xFF, (n) >> 8}, 2)

static uint8_t vga[0x30] = {
    0x00, 0x00, 0x00,
    0xAA, 0x00, 0x00,
    0x00, 0xAA, 0x00,
    0xAA, 0x55, 0x00,
    0x00, 0x00, 0xAA,
    0xAA, 0x00, 0xAA,
    0x00, 0xAA, 0xAA,
    0xAA, 0xAA, 0xAA,
    0x55, 0x55, 0x55,
    0xFF, 0x55, 0x55,
    0x55, 0xFF, 0x55,
    0xFF, 0xFF, 0x55,
    0x55, 0x55, 0xFF,
    0xFF, 0x55, 0xFF,
    0x55, 0xFF, 0xFF,
    0xFF, 0xFF, 0xFF,
};

struct Node {
    uint16_t key;
    struct Node *children[];
};
typedef struct Node Node;

static Node *
new_node(uint16_t key, int degree)
{
    Node *node = calloc(1, sizeof(*node) + degree * sizeof(Node *));
    if (node)
        node->key = key;
    return node;
}

static Node *
new_trie(int degree, int *nkeys)
{
    Node *root = new_node(0, degree);
    /* Create nodes for single pixels. */
    for (*nkeys = 0; *nkeys < degree; (*nkeys)++)
        root->children[*nkeys] = new_node(*nkeys, degree);
    *nkeys += 2; /* skip clear code and stop code */
    return root;
}

static void
del_trie(Node *root, int degree)
{
    if (!root)
        return;
    for (int i = 0; i < degree; i++)
        del_trie(root->children[i], degree);
    free(root);
}

#define write_and_store(s, dst, fd, src, n) \
do { \
    write(fd, src, n); \
    if (s) { \
        memcpy(dst, src, n); \
        dst += n; \
    } \
} while (0);

static void put_loop(ge_GIF *gif, uint16_t loop);

ge_GIF *ge_new_gif(const char *fname, uint16_t width, uint16_t height, int depth, int bgindex, int loop)
{
    ge_GIF* gif = calloc(1, sizeof(*gif) + width * height);
    if (!gif)
        goto no_gif;
    gif->w = width; gif->h = height;
    gif->bgindex = bgindex;
    gif->frame = (uint8_t*)&gif[1];
    gif->back = &gif->frame[width*height];
    gif->depth = depth;
#ifdef _WIN32
    gif->fd = creat(fname, S_IWRITE);
#else
    gif->fd = creat(fname, 0666);
#endif
    if (gif->fd == -1)
        goto no_fd;
#ifdef _WIN32
    setmode(gif->fd, O_BINARY);
#endif
    write(gif->fd, "GIF89a", 6);
    write_num(gif->fd, width);
    write_num(gif->fd, height);
    unsigned char flags = 0x70; // no GCT, 2^8 color in the original image (don't care), no sort, size of GCT 2^(7+1) (don't care) 
    write(gif->fd, (uint8_t []) {flags, (uint8_t) bgindex, 0x00}, 3); // background color = bgindex, ratio = 0 (no default ratio)
    put_loop(gif, (uint16_t) loop); // add the NETSCAPE 2.0 option for loop (loop = 0 infinite loop)
    return gif;
no_fd:
    free(gif);
no_gif:
    return NULL;
}

static void put_loop(ge_GIF *gif, uint16_t loop)
{
    write(gif->fd, (uint8_t []) {'!', 0xFF, 0x0B}, 3);
    write(gif->fd, "NETSCAPE2.0", 11);
    write(gif->fd, (uint8_t []) {0x03, 0x01}, 2);
    write_num(gif->fd, loop);
    write(gif->fd, "\0", 1);
}

/* Add packed key to buffer, updating offset and partial.
 *   gif->offset holds position to put next *bit*
 *   gif->partial holds bits to include in next byte */
static void put_key(ge_GIF *gif, uint16_t key, int key_size)
{
    int byte_offset, bit_offset, bits_to_write;
    byte_offset = gif->offset / 8;
    bit_offset = gif->offset % 8;
    gif->partial |= ((uint32_t) key) << bit_offset;
    bits_to_write = bit_offset + key_size;
    while (bits_to_write >= 8) {
        gif->buffer[byte_offset++] = gif->partial & 0xFF;
        if (byte_offset == 0xFF) {
            write(gif->fd, "\xFF", 1);
            write(gif->fd, gif->buffer, 0xFF);
            byte_offset = 0;
        }
        gif->partial >>= 8;
        bits_to_write -= 8;
    }
    gif->offset = (gif->offset + key_size) % (0xFF * 8);
}

static void end_key(ge_GIF *gif)
{
    int byte_offset;
    byte_offset = gif->offset / 8;
    if (gif->offset % 8)
        gif->buffer[byte_offset++] = gif->partial & 0xFF;
    if (byte_offset) {
        write(gif->fd, (uint8_t []) {byte_offset}, 1);
        write(gif->fd, gif->buffer, byte_offset);
    }
    write(gif->fd, "\0", 1);
    gif->offset = gif->partial = 0;
}

static void put_image(ge_GIF *gif, uint16_t w, uint16_t h, uint16_t x, uint16_t y, uint8_t* palette)
{
    int nkeys, key_size, i, j;
    Node *node, *child, *root;
    int degree = 1 << gif->depth;

    write(gif->fd, ",", 1);
    write_num(gif->fd, x);
    write_num(gif->fd, y);
    write_num(gif->fd, w);
    write_num(gif->fd, h);
    unsigned char lcd = 0x80 + gif->depth - 1;
    write(gif->fd, (uint8_t[]) { lcd }, 1); // gif->depth }, 2);// 0x80 because there is a local color table and there are 2^gif->depth colors in the table, we must write depth-1
    // we write the local color table
    int ncol = 3 * degree;
    write(gif->fd, palette, ncol);
    write(gif->fd, (uint8_t[]) { gif->depth }, 1); // gif->depth }, 2);// 0x80 because there is a local color table and there are 2^gif->depth colors in the table, we must write depth-1
    root = node = new_trie(degree, &nkeys);
    key_size = gif->depth + 1;
    put_key(gif, degree, key_size); /* clear code */
    for (i = y; i < y+h; i++) {
        for (j = x; j < x+w; j++) {
            uint8_t pixel = gif->frame[i*gif->w+j] & (degree - 1);
            child = node->children[pixel];
            if (child) {
                node = child;
            } else {
                put_key(gif, node->key, key_size);
                if (nkeys < 0x1000) {
                    if (nkeys == (1 << key_size))
                        key_size++;
                    node->children[pixel] = new_node(nkeys++, degree);
                } else {
                    put_key(gif, degree, key_size); /* clear code */
                    del_trie(root, degree);
                    root = node = new_trie(degree, &nkeys);
                    key_size = gif->depth + 1;
                }
                node = root->children[pixel];
            }
        }
    }
    put_key(gif, node->key, key_size);
    put_key(gif, degree + 1, key_size); /* stop code */
    end_key(gif);
    del_trie(root, degree);
}

static void add_graphics_control_extension(ge_GIF *gif, uint16_t d)
{
    uint8_t flags = 0;// 1;// 2 << 2 + 1;
    write(gif->fd, (uint8_t []) {'!', 0xF9, 0x04, flags}, 4);
    write_num(gif->fd, d);
    write(gif->fd, (uint8_t []) {0xFF, 0x00}, 2);
}

void ge_add_frame(ge_GIF *gif, uint8_t* palette, uint16_t delay)
{
    uint8_t *tmp;
    if (delay || (gif->bgindex >= 0))
        add_graphics_control_extension(gif, delay);
    put_image(gif, gif->w, gif->h, 0, 0, palette);
    gif->nframes++;
    if (gif->bgindex < 0) {
        tmp = gif->back;
        gif->back = gif->frame;
        gif->frame = tmp;
    }
}

void
ge_close_gif(ge_GIF* gif)
{
    write(gif->fd, ";", 1);
    close(gif->fd);
    free(gif);
}