输入源实例加入场景obs_scene_item

新创建的源obs_source_t只有加入场景”sence”中才可以进行渲染使用。只不过这里不是使用的obs_source类型，而是obs_scene_item

obs_scene_item 是场景中的项目，它是对 obs_source 的包装，包含了源在场景中的位置、缩放、旋转、裁剪等属性。

struct obs_scene_item {
    struct obs_scene *parent;         // 所属场景
    struct obs_source *source;        // 关联的源
    struct vec2 pos;                  // 位置
    struct vec2 scale;                // 缩放
    float rot;                        // 旋转角度
    bool visible;                     // 是否可见
    // ... 其他属性
};

AddSource函数如下：

static void AddSource(void *_data, obs_scene_t *scene)
{
    AddSourceData *data = (AddSourceData *)_data;
    obs_sceneitem_t *sceneitem;

    sceneitem = obs_scene_add(scene, data->source);

    if (data->transform != nullptr)
        obs_sceneitem_set_info2(sceneitem, data->transform);
    if (data->crop != nullptr)
        obs_sceneitem_set_crop(sceneitem, data->crop);
    if (data->blend_method != nullptr)
        obs_sceneitem_set_blending_method(sceneitem, *data->blend_method);
    if (data->blend_mode != nullptr)
        obs_sceneitem_set_blending_mode(sceneitem, *data->blend_mode);

    obs_sceneitem_set_visible(sceneitem, data->visible);
}

使用函数obs_scene_add将新源加入场景中。

obs_sceneitem_t *obs_scene_add(obs_scene_t *scene, obs_source_t *source)
{
    obs_sceneitem_t *item = obs_scene_add_internal(scene, source, NULL, 0);
    struct calldata params;
    uint8_t stack[128];

    if (!item)
        return NULL;

    calldata_init_fixed(&params, stack, sizeof(stack));
    calldata_set_ptr(&params, "scene", scene);
    calldata_set_ptr(&params, "item", item);
    signal_handler_signal(scene->source->context.signals, "item_add", &params);
    return item;
}

obs_scene_add_internal的功能如下：

static obs_sceneitem_t *obs_scene_add_internal(obs_scene_t *scene,
                           obs_source_t *source,
                           obs_sceneitem_t *insert_after,
                           int64_t id)
{
    struct obs_scene_item *last;
    struct obs_scene_item *item;
    pthread_mutex_t mutex;

    struct item_action action = {.visible = true, .timestamp = os_gettime_ns()};

    if (!scene)
        return NULL;

    //对需要被加入的源引用计数
    source = obs_source_get_ref(source);
    if (!source) {
        blog(LOG_ERROR, "Tried to add a NULL source to a scene");
        return NULL;
    }
...
    //这个与什么相关？
    if (!obs_source_add_active_child(scene->source, source)) {
        blog(LOG_WARNING, "Failed to add source to scene due to infinite source recursion");
        pthread_mutex_destroy(&mutex);
        goto release_source_and_fail;
    }

    item = bzalloc(sizeof(struct obs_scene_item));
    item->source = source; //源
    item->id = id ? id : ++scene->id_counter;
    item->parent = scene;
    item->ref = 1;
    item->align = OBS_ALIGN_TOP | OBS_ALIGN_LEFT;
    item->actions_mutex = mutex;
    item->user_visible = true;
    item->locked = false;
    item->is_group = strcmp(source->info.id, group_info.id) == 0;
    item->private_settings = obs_data_create();
    item->toggle_visibility = OBS_INVALID_HOTKEY_PAIR_ID;
    os_atomic_set_long(&item->active_refs, 1);
    vec2_set(&item->scale, 1.0f, 1.0f);
    matrix4_identity(&item->draw_transform);
    matrix4_identity(&item->box_transform);

    if (source_has_audio(source)) {
        item->visible = false;
        da_push_back(item->audio_actions, &action);
    } else {
        item->visible = true;
    }

    //item加入链表
    full_lock(scene);
    if (insert_after) {
        obs_sceneitem_t *next = insert_after->next;
        if (next)
            next->prev = item;
        item->next = insert_after->next;
        item->prev = insert_after;
        insert_after->next = item;
    } else {
        last = scene->first_item;
        if (!last) {
            scene->first_item = item;
        } else {
            while (last->next)
                last = last->next;

            last->next = item;
            item->prev = last;
        }
    }
    full_unlock(scene);
...
}

其实就是创建一个item,然后加入scene的item链表中。