Merge pull request #773 from MihailRis/background-assets-loader

background assets loader

doc/en/scripting/builtins/libassets.md

@@ -5,6 +5,13 @@ A library for working with audio/visual assets.
 ## Functions
 
 ```lua
+-- Requests background texture loading
+assets.request_texture(
+    -- Image file
+    filename: string,
+    -- Texture name after loading
+    name: string,
+)
 -- Loads a texture
 assets.load_texture(
     -- Array of bytes of an image file

doc/en/scripting/ui.md

@@ -167,10 +167,11 @@ Properties:
 
 Properties:
 
-| Name   | Type   | Read | Write | Description      |
-| ------ | ------ | ---- | ----- | ---------------- |
-| src    | string | yes  | yes   | texture name     |
-| region | vec4   | yes  | yes   | image sub-region |
+| Name     | Type   | Read | Write | Description      |
+| -------- | ------ | ---- | ----- | ---------------- |
+| src      | string | yes  | yes   | texture name     |
+| fallback | string | yes  | yes   | fallback texture |
+| region   | vec4   | yes  | yes   | image sub-region |
 
 ## Canvas
 

doc/en/xml-ui-layouts.md

@@ -120,6 +120,7 @@ Inner text is a button text.
 
 - `src` - name of an image stored in textures folder. Extension is not specified. Type: string.
   Example: *gui/error*
+- `fallback` - a fallback texture displayed when the main texture is missing / loading.
 - `region` - image region x1, y1, x2, y2 from 0.0, 0.0 (upper left corner), 1.0, 1.0 (lower right corner)
 
 ## *canvas*

doc/ru/scripting/builtins/libassets.md

@@ -5,6 +5,14 @@
 ## Функции
 
 ```lua
+-- Запрашивает фоновую загрузку текстуры
+assets.request_texture(
+    -- Файл изображения
+    filename: string,
+    -- Имя текстуры после загрузки
+    name: string,
+)
+
 -- Загружает текстуру
 assets.load_texture(
     -- Массив байт файла изображения
@@ -33,4 +41,4 @@ assets.to_canvas(
     -- так и находящиеся в атласе ("атлас:имя_текстуры").
     name: string
 ) -> Canvas
-```
+```

doc/ru/scripting/ui.md

@@ -170,6 +170,7 @@ document["worlds-panel"]:clear()
 | Название | Тип    | Чтение | Запись | Описание               |
 | -------- | ------ | ------ | ------ | ---------------------- |
 | src      | string | да     | да     | отображаемая текстура  |
+| fallback | string | да     | да     | резервная текстура     |
 | region   | vec4   | да     | да     | под-регион изображения |
 
 ## Холст (canvas)

doc/ru/xml-ui-layouts.md

@@ -121,6 +121,7 @@
 ## Изображение - *image*
 
 - `src` - имя изображения в папке textures без указания расширения. Тип: строка. Например `gui/error`
+- `fallback` - резервная текстура, отображаемая при отсутствии / фоновой загрузке основной
 - `region` - под-регион изображения x1, y1, x2, y2 от 0.0, 0.0 (левый верхний угол), 1.0, 1.0 (правый нижний угол)
 
 ## Холст - *canvas*

res/layouts/templates/pack.xml

@@ -11,5 +11,5 @@
     <label ifnot='%{error}' pos='80,28' size='355,50' multiline='true' color='#FFFFFFB2'>
         %{description}
     </label>
-    <image pos='8,8' src='%{icon}' size='64'/>
+    <image pos='8,8' src='%{icon}' fallback='gui/no_icon' size='64'/>
 </container>

res/layouts/templates/world.xml

@@ -4,7 +4,7 @@
     hover-color='#162B3399'
     onclick='app.open_world("%{name}")'
 >
-    <image pos='1' src='%{icon}' size='96,64'></image>
+    <image pos='1' src='%{icon}' fallback='gui/no_world_icon' size='96,64'></image>
     <label pos='104,8'>%{name}</label>
     <button margin='4'
             gravity='center-right'

src/assets/AssetsLoader.cpp

@@ -319,28 +319,31 @@ void AssetsLoader::addDefaults(AssetsLoader& loader, const Content* content) {
 }
 
 bool AssetsLoader::loadExternalTexture(
-    Assets* assets,
+    AssetsLoader& loader,
     const std::string& name,
     const std::vector<io::path>& alternatives
 ) {
-    if (assets->get<Texture>(name) != nullptr) {
+    if (loader.getAssets().get<Texture>(name) != nullptr) {
         return true;
     }
     for (auto& path : alternatives) {
         if (io::exists(path)) {
-            try {
-                auto image = imageio::read(path);
-                assets->store(Texture::from(image.get()), name);
-                return true;
-            } catch (const std::exception& err) {
-                logger.error() << "error while loading external "
-                               << path.string() << ": " << err.what();
-            }
+            loader.add(
+                AssetType::TEXTURE,
+                (path.parent() / path.stem()).string(),
+                name,
+                nullptr
+            );
+            return true;
         }
     }
     return false;
 }
 
+Assets& AssetsLoader::getAssets() {
+    return assets;
+}
+
 Engine& AssetsLoader::getEngine() {
     return engine;
 }
@@ -368,14 +371,24 @@ public:
     }
 };
 
-std::shared_ptr<Task> AssetsLoader::startTask(runnable onDone) {
+std::shared_ptr<Task> AssetsLoader::startTask(runnable onDone, int maxWorkers) {
     auto pool =
         std::make_shared<util::ThreadPool<aloader_entry, assetload::postfunc>>(
             "assets-loader-pool",
             [=]() { return std::make_shared<LoaderWorker>(this); },
-            [this](const assetload::postfunc& func) { func(&assets); }
+            [this](const assetload::postfunc& func) { func(&assets); },
+            maxWorkers
         );
     pool->setOnComplete(std::move(onDone));
+    pool->setJobsSource([this]() -> std::optional<aloader_entry> {
+        if (entries.empty()) {
+            return std::nullopt;
+        }
+        aloader_entry entry = std::move(entries.front());
+        entries.pop();
+        return entry;
+    });
+
     while (!entries.empty()) {
         aloader_entry entry = std::move(entries.front());
         entries.pop();

src/assets/AssetsLoader.hpp

@@ -113,7 +113,7 @@ public:
     /// @throws assetload::error
     void loadNext();
 
-    std::shared_ptr<Task> startTask(runnable onDone);
+    std::shared_ptr<Task> startTask(runnable onDone, int maxWorkers);
 
     const ResPaths& getPaths() const;
     aloader_func getLoader(AssetType tag);
@@ -124,10 +124,11 @@ public:
     static void addDefaults(AssetsLoader& loader, const Content* content);
 
     static bool loadExternalTexture(
-        Assets* assets,
+        AssetsLoader& loader,
         const std::string& name,
         const std::vector<io::path>& alternatives
     );
 
+    Assets& getAssets();
     Engine& getEngine();
 };

src/engine/AssetsManagement.cpp

@@ -0,0 +1,92 @@
+#include "AssetsManagement.hpp"
+
+#include "assets/AssetsLoader.hpp"
+#include "coders/GLSLExtension.hpp"
+#include "content/Content.hpp"
+#include "debug/Logger.hpp"
+#include "engine/Engine.hpp"
+#include "EnginePaths.hpp"
+#include "graphics/core/Shader.hpp"
+#include "graphics/render/ModelsGenerator.hpp"
+#include "graphics/ui/GUI.hpp"
+
+static debug::Logger logger("assets-management");
+
+AssetsManagement::AssetsManagement(Engine& engine)
+    : engine(engine), settings(engine.getSettings()) {
+}
+
+AssetsManagement::~AssetsManagement() {
+    finishBackgroundLoader();
+}
+
+const Assets* AssetsManagement::getStorage() const {
+    return assets.get();
+}
+
+Assets* AssetsManagement::getStorage() {
+    return assets.get();
+}
+
+AssetsLoader& AssetsManagement::acquireBackgroundLoader() {
+    if (backgroundLoader) {
+        return *backgroundLoader;
+    }
+    if (assets == nullptr) {
+        throw std::runtime_error("no assets storage available");
+    }
+    backgroundLoader = std::make_unique<AssetsLoader>(
+        engine, *assets, engine.getResPaths()
+    );
+    backgroundLoaderTask = backgroundLoader->startTask(
+        nullptr, settings.system.maxBgAssetLoaders.get()
+    );
+    return *backgroundLoader;
+}
+
+void AssetsManagement::loadAssets(Content* content) {
+    finishBackgroundLoader();
+
+    const auto& paths = engine.getPaths();
+    logger.info() << "loading assets";
+    Shader::preprocessor->setPaths(&paths.resPaths);
+
+    auto new_assets = std::make_unique<Assets>();
+    AssetsLoader loader(engine, *new_assets, paths.resPaths);
+    AssetsLoader::addDefaults(loader, content);
+
+    // no need
+    // correct log messages order is more useful
+    // todo: before setting to true, check if GLSLExtension thread safe 
+    bool threading = false; // look at three upper lines
+    if (threading) {
+        auto task = loader.startTask(
+            [=]() {}, 0
+        );
+        task->waitForEnd();
+    } else {
+        while (loader.hasNext()) {
+            loader.loadNext();
+        }
+    }
+    assets = std::move(new_assets);
+    if (content) {
+        ModelsGenerator::prepare(*content, *assets);
+    }
+    assets->setup();
+    engine.getGUI().onAssetsLoad(assets.get());
+}
+
+void AssetsManagement::update() {
+    if (backgroundLoaderTask) {
+        backgroundLoaderTask->update();
+    }
+}
+
+void AssetsManagement::finishBackgroundLoader() {
+    if (backgroundLoaderTask == nullptr) {
+        return;
+    }
+    backgroundLoaderTask.reset();
+    backgroundLoader.reset();
+}

src/engine/AssetsManagement.hpp

@@ -0,0 +1,33 @@
+#pragma once
+
+#include "assets/Assets.hpp"
+
+#include <memory>
+
+class AssetsLoader;
+class Engine;
+class Content;
+class Task;
+struct EngineSettings;
+
+class AssetsManagement final {
+public:
+    AssetsManagement(Engine& engine);
+    ~AssetsManagement();
+
+    void loadAssets(Content* content);
+    void update();
+    
+    Assets* getStorage();
+    const Assets* getStorage() const;
+
+    AssetsLoader& acquireBackgroundLoader();
+private:
+    void finishBackgroundLoader();
+
+    Engine& engine;
+    const EngineSettings& settings;
+    std::unique_ptr<Assets> assets;
+    std::unique_ptr<AssetsLoader> backgroundLoader;
+    std::shared_ptr<Task> backgroundLoaderTask;
+};

src/engine/Engine.cpp

@@ -4,47 +4,45 @@
 #define GLEW_STATIC
 #endif
 
-#include "debug/Logger.hpp"
-#include "assets/AssetsLoader.hpp"
+#include "AssetsManagement.hpp"
 #include "audio/audio.hpp"
+#include "coders/commons.hpp"
 #include "coders/GLSLExtension.hpp"
 #include "coders/toml.hpp"
-#include "coders/commons.hpp"
-#include "devtools/Editor.hpp"
-#include "devtools/Project.hpp"
-#include "devtools/DebuggingServer.hpp"
 #include "content/ContentControl.hpp"
 #include "core_defs.hpp"
-#include "io/io.hpp"
-#include "io/settings_io.hpp"
+#include "debug/Logger.hpp"
+#include "devtools/DebuggingServer.hpp"
+#include "devtools/Editor.hpp"
+#include "devtools/Project.hpp"
+#include "EnginePaths.hpp"
 #include "frontend/locale.hpp"
 #include "frontend/menu.hpp"
 #include "frontend/screens/Screen.hpp"
-#include "graphics/render/ModelsGenerator.hpp"
 #include "graphics/core/DrawContext.hpp"
 #include "graphics/core/Shader.hpp"
-#include "graphics/ui/GUI.hpp"
 #include "graphics/ui/elements/Menu.hpp"
-#include "logic/EngineController.hpp"
+#include "graphics/ui/GUI.hpp"
+#include "io/io.hpp"
+#include "io/settings_io.hpp"
 #include "logic/CommandsInterpreter.hpp"
-#include "logic/scripting/scripting.hpp"
+#include "logic/EngineController.hpp"
 #include "logic/scripting/scripting_hud.hpp"
+#include "logic/scripting/scripting.hpp"
+#include "Mainloop.hpp"
 #include "network/Network.hpp"
+#include "ServerMainloop.hpp"
 #include "util/platform.hpp"
+#include "util/stringutil.hpp"
 #include "window/input.hpp"
 #include "window/Window.hpp"
-#include "world/Level.hpp"
-#include "Mainloop.hpp"
-#include "ServerMainloop.hpp"
 #include "WindowControl.hpp"
-#include "EnginePaths.hpp"
+#include "world/Level.hpp"
 
-#include <iostream>
 #include <assert.h>
 #include <glm/glm.hpp>
 #include <unordered_set>
 #include <functional>
-#include <utility>
 
 static debug::Logger logger("engine");
 
@@ -84,6 +82,7 @@ void Engine::onContentLoad() {
 }
 
 void Engine::initializeClient() {
+    assets = std::make_unique<AssetsManagement>(*this);
     windowControl = std::make_unique<WindowControl>(*this);
     auto [window, input] = windowControl->initialize();
 
@@ -264,6 +263,7 @@ void Engine::applicationTick() {
 
 void Engine::updateFrontend() {
     double delta = time.getDelta();
+    assets->update();
     updateHotkeys();
     audio::update(delta);
     gui->act(delta, window->getSize());
@@ -305,7 +305,7 @@ void Engine::renderFrame() {
     screen->draw(time.getDelta());
 
     DrawContext ctx(nullptr, *window, nullptr);
-    gui->draw(ctx, *assets);
+    gui->draw(ctx, *assets->getStorage());
 }
 
 void Engine::saveSettings() {
@@ -363,33 +363,7 @@ void Engine::setLevelConsumer(OnWorldOpen levelConsumer) {
 }
 
 void Engine::loadAssets() {
-    logger.info() << "loading assets";
-    Shader::preprocessor->setPaths(&paths->resPaths);
-
-    auto content = this->content->get();
-
-    auto new_assets = std::make_unique<Assets>();
-    AssetsLoader loader(*this, *new_assets, paths->resPaths);
-    AssetsLoader::addDefaults(loader, content);
-
-    // no need
-    // correct log messages order is more useful
-    // todo: before setting to true, check if GLSLExtension thread safe
-    bool threading = false; // look at three upper lines
-    if (threading) {
-        auto task = loader.startTask([=](){});
-        task->waitForEnd();
-    } else {
-        while (loader.hasNext()) {
-            loader.loadNext();
-        }
-    }
-    assets = std::move(new_assets);
-    if (content) {
-        ModelsGenerator::prepare(*content, *assets);
-    }
-    assets->setup();
-    gui->onAssetsLoad(assets.get());
+    assets->loadAssets(content->get());
 }
 
 void Engine::loadProject() {
@@ -442,7 +416,11 @@ EngineSettings& Engine::getSettings() {
 }
 
 Assets* Engine::getAssets() {
-    return assets.get();
+    return assets->getStorage();
+}
+
+AssetsLoader& Engine::acquireBackgroundLoader() {
+    return assets->acquireBackgroundLoader();
 }
 
 EnginePaths& Engine::getPaths() {

src/engine/Engine.hpp

@@ -10,6 +10,8 @@
 #include <string>
 
 class Assets;
+class AssetsLoader;
+class AssetsManagement;
 class ContentControl;
 class EngineController;
 class EnginePaths;
@@ -52,7 +54,7 @@ class Engine : public util::ObjectsKeeper {
     std::unique_ptr<EnginePaths> paths;
     std::unique_ptr<Project> project;
     std::unique_ptr<SettingsHandler> settingsHandler;
-    std::unique_ptr<Assets> assets;
+    std::unique_ptr<AssetsManagement> assets;
     std::shared_ptr<Screen> screen;
     std::unique_ptr<ContentControl> content;
     std::unique_ptr<EngineController> controller;
@@ -109,6 +111,8 @@ public:
     /// @brief Get active assets storage instance
     Assets* getAssets();
 
+    AssetsLoader& acquireBackgroundLoader();
+
     /// @brief Get writeable engine settings structure instance
     EngineSettings& getSettings();
 

src/engine/EnginePaths.cpp

@@ -274,6 +274,9 @@ ResPaths::ResPaths(std::vector<PathsRoot> roots)
 }
 
 io::path ResPaths::find(const std::string& filename) const {
+    if (filename.find(':') != std::string::npos) {
+        return filename;
+    }
     for (int i = roots.size() - 1; i >= 0; i--) {
         auto& root = roots[i];
         auto file = root.path / filename;

src/graphics/ui/elements/Image.cpp

@@ -3,6 +3,7 @@
 #include <utility>
 
 #include "assets/Assets.hpp"
+#include "assets/assets_util.hpp"
 #include "graphics/core/Atlas.hpp"
 #include "graphics/core/Batch2D.hpp"
 #include "graphics/core/DrawContext.hpp"
@@ -16,37 +17,25 @@ Image::Image(GUI& gui, std::string texture, glm::vec2 size)
     setInteractive(false);
 }
 
+util::TextureRegion Image::refreshTexture(const Assets& assets) {
+    auto region = util::get_texture_region(assets, texture, fallback);
+    if (region.texture && autoresize) {
+        setSize(glm::vec2(
+            region.texture->getWidth() * region.region.getWidth(),
+            region.texture->getHeight() * region.region.getHeight()
+        ));
+    }
+    return region;
+}
+
 void Image::draw(const DrawContext& pctx, const Assets& assets) {
     glm::vec2 pos = calcPos();
     auto batch = pctx.getBatch2D();
 
-    Texture* texture = nullptr;
-    auto separator = this->texture.find(':');
-    if (separator == std::string::npos) {
-        texture = assets.get<Texture>(this->texture);
-        batch->texture(texture);
-        if (texture && autoresize) {
-            setSize(glm::vec2(texture->getWidth(), texture->getHeight()));
-        }
-    } else {
-        auto atlasName = this->texture.substr(0, separator);
-        if (auto atlas = assets.get<Atlas>(atlasName)) {
-            if (auto region =
-                    atlas->getIf(this->texture.substr(separator + 1))) {
-                texture = atlas->getTexture();
-                batch->texture(atlas->getTexture());
-                batch->setRegion(*region);
-                if (autoresize) {
-                    setSize(glm::vec2(
-                        texture->getWidth() * region->getWidth(),
-                        texture->getHeight() * region->getHeight()
-                    ));
-                }
-            } else {
-                batch->texture(nullptr);
-            }
-        }
-    }
+    auto textureRegion = refreshTexture(assets);
+    
+    batch->setRegion(textureRegion.region);
+    batch->texture(textureRegion.texture);
     batch->rect(
         pos.x,
         pos.y,
@@ -73,10 +62,18 @@ const std::string& Image::getTexture() const {
     return texture;
 }
 
+const std::string& Image::getFallback() const {
+    return fallback;
+}
+
 void Image::setTexture(const std::string& name) {
     texture = name;
 }
 
+void Image::setFallback(const std::string& name) {
+    fallback = name;
+}
+
 void Image::setRegion(const UVRegion& region) {
     this->region = region;
 }

src/graphics/ui/elements/Image.hpp

@@ -3,21 +3,30 @@
 #include "UINode.hpp"
 #include "maths/UVRegion.hpp"
 
+namespace util {
+    struct TextureRegion;
+}
+
 namespace gui {
-    class Image : public UINode {
+    class Image final : public UINode {
     protected:
         std::string texture;
+        std::string fallback;
         UVRegion region {};
         bool autoresize = false;
+
+        util::TextureRegion refreshTexture(const Assets& assets);
     public:
         Image(GUI& gui, std::string texture, glm::vec2 size=glm::vec2(32,32));
 
-        virtual void draw(const DrawContext& pctx, const Assets& assets) override;
+        void draw(const DrawContext& pctx, const Assets& assets) override;
 
-        virtual void setAutoResize(bool flag);
-        virtual bool isAutoResize() const;
-        virtual const std::string& getTexture() const;
-        virtual void setTexture(const std::string& name);
+        void setAutoResize(bool flag);
+        bool isAutoResize() const;
+        const std::string& getTexture() const;
+        const std::string& getFallback() const;
+        void setTexture(const std::string& name);
+        void setFallback(const std::string& name);
         void setRegion(const UVRegion& region);
         const UVRegion& getRegion() const;
     };

src/graphics/ui/gui_xml.cpp

@@ -632,8 +632,10 @@ static std::shared_ptr<UINode> read_image(
     const UiXmlReader& reader, const xml::xmlelement& element
 ) {
     std::string src = element.attr("src", "").getText();
-    auto image = std::make_shared<Image>(reader.getGUI(), src);
+    std::string fallback = element.attr("fallback", "").getText();
+    auto image = std::make_shared<Image>(reader.getGUI(), std::move(src));
     read_uinode(reader, element, *image);
+    image->setFallback(std::move(fallback));
 
     if (element.has("region")) {
         auto vec = element.attr("region").asVec4();

src/io/settings_io.cpp

@@ -94,6 +94,9 @@ SettingsHandler::SettingsHandler(EngineSettings& settings) {
     builder.add("do-write-lights", &settings.debug.doWriteLights);
     builder.add("do-trace-shaders", &settings.debug.doTraceShaders);
     builder.add("enable-experimental", &settings.debug.enableExperimental);
+
+    builder.addSection("system");
+    builder.add("max-bg-asset-loaders", &settings.system.maxBgAssetLoaders);
 }
 
 dv::value SettingsHandler::getValue(const std::string& name) const {

src/logic/scripting/lua/libs/libassets.cpp

@@ -1,6 +1,7 @@
 #include "api_lua.hpp"
 
 #include "assets/Assets.hpp"
+#include "assets/AssetsLoader.hpp"
 #include "coders/png.hpp"
 #include "coders/vcm.hpp"
 #include "debug/Logger.hpp"
@@ -24,6 +25,14 @@ static void load_texture(
     }
 }
 
+static int l_request_texture(lua::State* L) {
+    std::string filename = lua::require_string(L, 1);
+    std::string alias = lua::require_string(L, 2);
+    auto& loader = engine->acquireBackgroundLoader();
+    loader.add(AssetType::TEXTURE, filename, alias);
+    return 0;
+}
+
 static int l_load_texture(lua::State* L) {
     if (lua::isstring(L, 3) && lua::require_lstring(L, 3) != "png") {
         throw std::runtime_error("unsupportd image format");
@@ -108,6 +117,7 @@ static int l_to_canvas(lua::State* L) {
 }
 
 const luaL_Reg assetslib[] = {
+    {"request_texture", lua::wrap<l_request_texture>},
     {"load_texture", lua::wrap<l_load_texture>},
     {"parse_model", lua::wrap<l_parse_model>},
     {"to_canvas", lua::wrap<l_to_canvas>},

src/logic/scripting/lua/libs/libgui.cpp

@@ -397,6 +397,13 @@ static int p_get_src(UINode* node, lua::State* L) {
     return 0;
 }
 
+static int p_get_fallback(UINode* node, lua::State* L) {
+    if (auto image = dynamic_cast<Image*>(node)) {
+        return lua::pushstring(L, image->getFallback());
+    }
+    return 0;
+}
+
 static int p_get_region(UINode* node, lua::State* L) {
     if (auto image = dynamic_cast<Image*>(node)) {
         const auto& region = image->getRegion();
@@ -663,6 +670,7 @@ static int l_gui_getattr(lua::State* L) {
             {"syntax", p_get_syntax},
             {"markup", p_get_markup},
             {"src", p_get_src},
+            {"fallback", p_get_fallback},
             {"value", p_get_value},
             {"min", p_get_min},
             {"max", p_get_max},
@@ -790,6 +798,11 @@ static void p_set_src(UINode* node, lua::State* L, int idx) {
         modelviewer->setModel(lua::require_string(L, idx));
     }
 }
+static void p_set_fallback(UINode* node, lua::State* L, int idx) {
+    if (auto image = dynamic_cast<Image*>(node)) {
+        image->setFallback(lua::require_string(L, idx));
+    }
+}
 static void p_set_region(UINode* node, lua::State* L, int idx) {
     if (auto image = dynamic_cast<Image*>(node)) {
         auto vec = lua::tovec4(L, idx);
@@ -962,6 +975,7 @@ static int l_gui_setattr(lua::State* L) {
             {"syntax", p_set_syntax},
             {"markup", p_set_markup},
             {"src", p_set_src},
+            {"fallback", p_set_fallback},
             {"caret", p_set_caret},
             {"value", p_set_value},
             {"min", p_set_min},

src/logic/scripting/lua/libs/libpack.cpp

@@ -87,10 +87,10 @@ static int l_pack_get_info(
     lua::setfield(L, "path");
 
     if (!engine->isHeadless()) {
-        auto assets = engine->getAssets();
+        auto& assetsLoader = engine->acquireBackgroundLoader();
         std::string icon = pack.id + ".icon";
         if (!AssetsLoader::loadExternalTexture(
-                assets, icon, {pack.folder / "icon.png"}
+                assetsLoader, icon, {pack.folder / "icon.png"}
             )) {
             icon = "gui/no_icon";
         }

src/logic/scripting/lua/libs/libworld.cpp

@@ -56,10 +56,9 @@ static int l_get_list(lua::State* L) {
         lua::pushstring(L, name);
         lua::setfield(L, "name");
 
-        auto assets = engine->getAssets();
         std::string icon = "world#" + name + ".icon";
         if (!engine->isHeadless() && !AssetsLoader::loadExternalTexture(
-                assets,
+                engine->acquireBackgroundLoader(),
                 icon,
                 {worlds[i] / "icon.png",
                  worlds[i] / "preview.png"}

src/settings.hpp

@@ -115,6 +115,10 @@ struct UiSettings {
 struct NetworkSettings {
 };
 
+struct SystemSettings {
+    IntegerSetting maxBgAssetLoaders {3, -4, 16};
+};
+
 struct EngineSettings {
     AudioSettings audio;
     DisplaySettings display;
@@ -125,4 +129,5 @@ struct EngineSettings {
     UiSettings ui;
     NetworkSettings network;
     PathfindingSettings pathfinding;
+    SystemSettings system;
 };

src/util/ThreadPool.hpp

@@ -2,6 +2,7 @@
 
 #include <atomic>
 #include <chrono>
+#include <optional>
 #include <condition_variable>
 #include <functional>
 #include <iostream>
@@ -48,6 +49,7 @@ namespace util {
         std::atomic<int> busyWorkers = 0;
         std::atomic<uint> jobsDone = 0;
         std::atomic<bool> working = true;
+        supplier<std::optional<T>> jobsSource = nullptr;
         bool failed = false;
         bool standaloneResults = true;
         bool stopOnFail = true;
@@ -151,6 +153,10 @@ namespace util {
             return working;
         }
 
+        void setJobsSource(supplier<std::optional<T>>&& source) {
+            jobsSource = std::move(source);
+        }
+
         void terminate() override {
             if (!working) {
                 return;
@@ -221,6 +227,22 @@ namespace util {
                     }
                 }
             }
+            if (jobsSource) {
+                bool jobsAdded = false;
+                std::lock_guard<std::mutex> jobsLock(jobsMutex);
+                while (true) {
+                    auto job = jobsSource();
+                    if (job.has_value()) {
+                        jobs.push(std::move(job.value()));
+                        jobsAdded = true;
+                    } else {
+                        break;
+                    }
+                }
+                if (jobsAdded) {
+                    jobsMutexCondition.notify_one();
+                }
+            }
             if (failed) {
                 throw std::runtime_error("some job failed");
             }