zbar中的zbar_scan_image 函数

        图像扫描的工作都是由zbar_scan_image完成的，zbar_scan_image主要根据设定的扫描密度(density)控制像素点读取(Z字形)，scanner.c文件内的zbar_scan_y()来完成滤波，阈值，确定边缘，转化成宽度流。

int zbar_scan_image (zbar_image_scanner_t *iscn,
                     zbar_image_t *img)
{
    /* timestamp image
     * FIXME prefer video timestamp
     */
#if _POSIX_TIMERS > 0
    struct timespec abstime;
    clock_gettime(CLOCK_REALTIME, &abstime);
    iscn->time = (abstime.tv_sec * 1000) + ((abstime.tv_nsec / 500000) + 1) / 2;
#else
    struct timeval abstime;
    gettimeofday(&abstime, NULL);
    iscn->time = (abstime.tv_sec * 1000) + ((abstime.tv_usec / 500) + 1) / 2;
#endif

#ifdef ENABLE_QRCODE
    _zbar_qr_reset(iscn->qr);
#endif

    /* get grayscale image, convert if necessary */
    if(img->format != fourcc('Y','8','0','0') &&
       img->format != fourcc('G','R','E','Y'))
        return(-1);
    iscn->img = img;

    /* recycle previous scanner and image results */
    zbar_image_scanner_recycle_image(iscn, img);
    zbar_symbol_set_t *syms = iscn->syms;
    if(!syms) {
        syms = iscn->syms = _zbar_symbol_set_create();
        STAT(syms_new);
        zbar_symbol_set_ref(syms, 1);
    }
    else
        zbar_symbol_set_ref(syms, 2);
    img->syms = syms;

    unsigned w = img->width;
    unsigned h = img->height;
    const uint8_t *data = img->data;

    zbar_image_write_png(img, "debug.png");
    svg_open("debug.svg", 0, 0, w, h);
    svg_image("debug.png", w, h);

    zbar_scanner_t *scn = iscn->scn;

    int density = CFG(iscn, ZBAR_CFG_Y_DENSITY);
    if(density > 0) {
        svg_group_start("scanner", 0, 1, 1, 0, 0);
        const uint8_t *p = data;
        int x = 0, y = 0;
        iscn->dy = 0;

        int border = (((h - 1) % density) + 1) / 2;
        if(border > h / 2)
            border = h / 2;
        movedelta(0, border);
        iscn->v = y;

        zbar_scanner_new_scan(scn);

        while(y < h) {
            zprintf(128, "img_x+: %04d,%04d @%p\n", x, y, p);
            svg_path_start("vedge", 1. / 32, 0, y + 0.5);
            iscn->dx = iscn->du = 1;
            iscn->umin = 0;
            while(x < w) {
                uint8_t d = *p;
                movedelta(1, 0);
                zbar_scan_y(scn, d);
            }
            ASSERT_POS;
            quiet_border(iscn);
            svg_path_end();

            movedelta(-1, density);
            iscn->v = y;
            if(y >= h)
                break;

            zprintf(128, "img_x-: %04d,%04d @%p\n", x, y, p);
            svg_path_start("vedge", -1. / 32, w, y + 0.5);
            iscn->dx = iscn->du = -1;
            iscn->umin = w;
            while(x >= 0) {
                uint8_t d = *p;
                movedelta(-1, 0);
                zbar_scan_y(scn, d);
            }
            ASSERT_POS;
            quiet_border(iscn);
            svg_path_end();

            movedelta(1, density);
            iscn->v = y;
        }
        svg_group_end();
    }
    iscn->dx = 0;

    density = CFG(iscn, ZBAR_CFG_X_DENSITY);
    if(density > 0) {
        svg_group_start("scanner", 90, 1, -1, 0, 0);
        const uint8_t *p = data;
        int x = 0, y = 0;

        int border = (((w - 1) % density) + 1) / 2;
        if(border > w / 2)
            border = w / 2;
        movedelta(border, 0);
        iscn->v = x;

        while(x < w) {
            zprintf(128, "img_y+: %04d,%04d @%p\n", x, y, p);
            svg_path_start("vedge", 1. / 32, 0, x + 0.5);
            iscn->dy = iscn->du = 1;
            iscn->umin = 0;
            while(y < h) {
                uint8_t d = *p;
                movedelta(0, 1);
                zbar_scan_y(scn, d);
            }
            ASSERT_POS;
            quiet_border(iscn);
            svg_path_end();

            movedelta(density, -1);
            iscn->v = x;
            if(x >= w)
                break;

            zprintf(128, "img_y-: %04d,%04d @%p\n", x, y, p);
            svg_path_start("vedge", -1. / 32, h, x + 0.5);
            iscn->dy = iscn->du = -1;
            iscn->umin = h;
            while(y >= 0) {
                uint8_t d = *p;
                movedelta(0, -1);
                zbar_scan_y(scn, d);
            }
            ASSERT_POS;
            quiet_border(iscn);
            svg_path_end();

            movedelta(density, 1);
            iscn->v = x;
        }
        svg_group_end();
    }
    iscn->dy = 0;
    iscn->img = NULL;

#ifdef ENABLE_QRCODE
    _zbar_qr_decode(iscn->qr, iscn, img);
#endif

    /* FIXME tmp hack to filter bad EAN results */
    if(syms->nsyms && !iscn->enable_cache &&
       (density == 1 || CFG(iscn, ZBAR_CFG_Y_DENSITY) == 1)) {
        zbar_symbol_t **symp = &syms->head, *sym;
        while((sym = *symp)) {
            if(sym->type < ZBAR_I25 && sym->type > ZBAR_PARTIAL &&
               sym->quality < 3) {
                /* recycle */
                *symp = sym->next;
                syms->nsyms--;
                sym->next = NULL;
                _zbar_image_scanner_recycle_syms(iscn, sym);
            }
            else
                symp = &sym->next;
        }
    }

    if(syms->nsyms && iscn->handler)
        iscn->handler(img, iscn->userdata);

    svg_close();
    return(syms->nsyms);
}