Add themes to form loading (Issue #325)

changelog.md

@@ -1,6 +1,12 @@
 TGUI 1.13  (TBD)
 ----------------
 
+- Implemented support for themes in forms ([Issue #325](https://github.com/texus/TGUI/issues/325)):
+  - `loadWidgetsFromStream` now clears and restores the default theme during load, matching `loadWidgetsFromFile`
+  - `FormLoadOptions::applyDefaultTheme` keeps the global default theme active during form load so widgets without a `Renderer` property match programmatic construction
+  - Form files may declare top-level `Theme.<Alias>` sections with per-section renderer fallbacks (`Button = &1;`, etc.)
+  - `Renderer = @Alias` / `@Alias.Section` bind to runtime themes (`FormLoadOptions::themesByAlias`) or form fallbacks
+  - Form loading calls non-virtual `Widget::load(node, WidgetLoadResources)`, which sets a short-lived load context then dispatches to virtual `load(node, LoadingRenderersMap)` so custom widget subclasses keep a single override; `load(map)` builds a full `WidgetLoadResources` (including themes) and calls `Widget::loadUsingResources`
 - Added Emscripten support
 - Each tab in Tabs and VerticalTabs widgets can now be assigned a unique id
 - Position and size layout expressions weren't saved when the result equaled (0,0)

include/TGUI/Backend/Window/BackendGui.hpp

@@ -470,6 +470,11 @@ namespace tgui
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         void loadWidgetsFromFile(const String& filename, bool replaceExisting = true);
 
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Loads the child widgets from a text file with load options
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void loadWidgetsFromFile(const String& filename, bool replaceExisting, const FormLoadOptions& options);
+
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         /// @brief Saves the child widgets to a text file
         ///
@@ -495,6 +500,16 @@ namespace tgui
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         void loadWidgetsFromStream(std::stringstream&& stream, bool replaceExisting = true);
 
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Loads the child widgets from a string stream with load options
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void loadWidgetsFromStream(std::stringstream& stream, bool replaceExisting, const FormLoadOptions& options);
+
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Loads the child widgets from a string stream with load options
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void loadWidgetsFromStream(std::stringstream&& stream, bool replaceExisting, const FormLoadOptions& options);
+
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         /// @brief Saves this the child widgets to a text file
         ///

include/TGUI/Container.hpp

@@ -25,6 +25,7 @@
 #ifndef TGUI_CONTAINER_HPP
 #define TGUI_CONTAINER_HPP
 
+#include <TGUI/FormLoadOptions.hpp>
 #include <TGUI/Widget.hpp>
 
 /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -196,6 +197,11 @@ namespace tgui
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         void loadWidgetsFromFile(const String& filename, bool replaceExisting = true);
 
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Loads the child widgets from a text file with load options
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void loadWidgetsFromFile(const String& filename, bool replaceExisting, const FormLoadOptions& options);
+
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         /// @brief Saves the child widgets to a text file
         ///
@@ -221,6 +227,16 @@ namespace tgui
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         void loadWidgetsFromStream(std::stringstream&& stream, bool replaceExisting = true);
 
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Loads the child widgets from a string stream with load options
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void loadWidgetsFromStream(std::stringstream& stream, bool replaceExisting, const FormLoadOptions& options);
+
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Loads the child widgets from a string stream with load options
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void loadWidgetsFromStream(std::stringstream&& stream, bool replaceExisting, const FormLoadOptions& options);
+
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         /// @brief Saves the child widgets to a text file
         ///
@@ -615,7 +631,9 @@ namespace tgui
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         // Mutual code in loadWidgetsFromFile and loadWidgetsFromStream
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
-        void loadWidgetsImpl(const std::unique_ptr<DataIO::Node>& rootNode, bool replaceExisting);
+        void loadWidgetsImpl(const std::unique_ptr<DataIO::Node>& rootNode, bool replaceExisting, const FormLoadOptions& options);
+
+        void loadWidgetsFromNodeTree(const std::unique_ptr<DataIO::Node>& rootNode, bool replaceExisting, const FormLoadOptions& options);
 
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
@@ -635,6 +653,11 @@ namespace tgui
 
         friend class SubwidgetContainer; // Needs access to save and load functions
 
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @internal
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void loadContainedWidgetsFromNodes(const std::unique_ptr<DataIO::Node>& node, const WidgetLoadResources& resources);
+
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
     };
 

include/TGUI/FormLoadOptions.hpp

@@ -0,0 +1,50 @@
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// TGUI - Texus' Graphical User Interface
+// Copyright (C) 2012-2026 Bruno Van de Velde (vdv_b@tgui.eu)
+//
+// This software is provided 'as-is', without any express or implied warranty.
+// In no event will the authors be held liable for any damages arising from the use of this software.
+//
+// Permission is granted to anyone to use this software for any purpose,
+// including commercial applications, and to alter it and redistribute it freely,
+// subject to the following restrictions:
+//
+// 1. The origin of this software must not be misrepresented;
+//    you must not claim that you wrote the original software.
+//    If you use this software in a product, an acknowledgment
+//    in the product documentation would be appreciated but is not required.
+//
+// 2. Altered source versions must be plainly marked as such,
+//    and must not be misrepresented as being the original software.
+//
+// 3. This notice may not be removed or altered from any source distribution.
+//
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+#ifndef TGUI_FORM_LOAD_OPTIONS_HPP
+#define TGUI_FORM_LOAD_OPTIONS_HPP
+
+#include <TGUI/Loading/Theme.hpp>
+#include <TGUI/String.hpp>
+
+#include <map>
+#include <memory>
+
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+namespace tgui
+{
+    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    /// @brief Options for loading widget forms
+    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    struct TGUI_API FormLoadOptions
+    {
+        std::map<String, Theme::Ptr> themesByAlias;
+        bool applyDefaultTheme = false;
+    };
+} // namespace tgui
+
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+#endif // TGUI_FORM_LOAD_OPTIONS_HPP

include/TGUI/ScopeExit.hpp

@@ -0,0 +1,90 @@
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// TGUI - Texus' Graphical User Interface
+// Copyright (C) 2012-2026 Bruno Van de Velde (vdv_b@tgui.eu)
+//
+// This software is provided 'as-is', without any express or implied warranty.
+// In no event will the authors be held liable for any damages arising from the use of this software.
+//
+// Permission is granted to anyone to use this software for any purpose,
+// including commercial applications, and to alter it and redistribute it freely,
+// subject to the following restrictions:
+//
+// 1. The origin of this software must not be misrepresented;
+//    you must not claim that you wrote the original software.
+//    If you use this software in a product, an acknowledgment
+//    in the product documentation would be appreciated but is not required.
+//
+// 2. Altered source versions must be plainly marked as such,
+//    and must not be misrepresented as being the original software.
+//
+// 3. This notice may not be removed or altered from any source distribution.
+//
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+#ifndef TGUI_SCOPE_EXIT_HPP
+#define TGUI_SCOPE_EXIT_HPP
+
+#include <TGUI/Config.hpp>
+
+#include <type_traits>
+#include <utility>
+
+namespace tgui
+{
+    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    /// @brief Invokes a function when leaving scope (return or exception). Not included from TGUI.hpp; include explicitly if needed.
+    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    template <typename F>
+    class ScopeExit
+    {
+    public:
+        template <typename G, typename = typename std::enable_if<!std::is_same<typename std::decay<G>::type, ScopeExit>::value>::type>
+        explicit ScopeExit(G&& func) :
+            m_func(std::forward<G>(func)),
+            m_active(true)
+        {
+        }
+
+        ScopeExit(const ScopeExit&) = delete;
+
+        ScopeExit& operator=(const ScopeExit&) = delete;
+        ScopeExit& operator=(ScopeExit&&) = delete;
+
+        ScopeExit(ScopeExit&& other) noexcept(std::is_nothrow_move_constructible<F>::value) :
+            m_func(std::move(other.m_func)),
+            m_active(other.m_active)
+        {
+            other.m_active = false;
+        }
+
+        ~ScopeExit()
+        {
+            if (m_active)
+                m_func();
+        }
+
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Skip invoking the function when the guard is destroyed
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void release() noexcept
+        {
+            m_active = false;
+        }
+
+    private:
+        F m_func;
+        bool m_active;
+    };
+
+    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    /// @brief Helper to create a ScopeExit without naming the lambda's type
+    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    template <typename F>
+    TGUI_NODISCARD ScopeExit<typename std::decay<F>::type> makeScopeExit(F&& func)
+    {
+        return ScopeExit<typename std::decay<F>::type>(std::forward<F>(func));
+    }
+} // namespace tgui
+
+#endif // TGUI_SCOPE_EXIT_HPP

include/TGUI/Widget.hpp

@@ -45,6 +45,7 @@
 #include <TGUI/Sprite.hpp>
 #include <TGUI/String.hpp>
 #include <TGUI/Vector2.hpp>
+#include <TGUI/WidgetLoadResources.hpp>
 
 #include <unordered_set>
 
@@ -111,6 +112,11 @@ namespace tgui
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         virtual ~Widget();
 
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Loads the widget from a form node (with theme resources)
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void load(const std::unique_ptr<DataIO::Node>& node, const WidgetLoadResources& resources);
+
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         /// @brief Overload of copy assignment operator
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
@@ -1159,6 +1165,11 @@ namespace tgui
         using SavingRenderersMap = std::map<const Widget*, std::pair<std::unique_ptr<DataIO::Node>, String>>;
         using LoadingRenderersMap = std::map<String, std::shared_ptr<RendererData>>;
 
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        /// @brief Loads widget fields from a form node using the given resources
+        /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+        void loadUsingResources(const std::unique_ptr<DataIO::Node>& node, const WidgetLoadResources& resources);
+
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
         /// @brief Function called when one of the properties of the renderer is changed
         ///
@@ -1313,6 +1324,9 @@ namespace tgui
         bool m_transparentTextureCached = false;
         unsigned int m_textSizeCached = 0;
 
+        const std::map<String, std::shared_ptr<Theme>>* m_loadRuntimeThemesByAlias = nullptr;
+        const ThemeFallbackMap* m_loadThemeFallbacks = nullptr;
+
         /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
 
         friend class Container; // Container accesses save and load functions

include/TGUI/WidgetLoadResources.hpp

@@ -0,0 +1,62 @@
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+//
+// TGUI - Texus' Graphical User Interface
+// Copyright (C) 2012-2026 Bruno Van de Velde (vdv_b@tgui.eu)
+//
+// This software is provided 'as-is', without any express or implied warranty.
+// In no event will the authors be held liable for any damages arising from the use of this software.
+//
+// Permission is granted to anyone to use this software for any purpose,
+// including commercial applications, and to alter it and redistribute it freely,
+// subject to the following restrictions:
+//
+// 1. The origin of this software must not be misrepresented;
+//    you must not claim that you wrote the original software.
+//    If you use this software in a product, an acknowledgment
+//    in the product documentation would be appreciated but is not required.
+//
+// 2. Altered source versions must be plainly marked as such,
+//    and must not be misrepresented as being the original software.
+//
+// 3. This notice may not be removed or altered from any source distribution.
+//
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+#ifndef TGUI_WIDGET_LOAD_RESOURCES_HPP
+#define TGUI_WIDGET_LOAD_RESOURCES_HPP
+
+#include <TGUI/Renderers/WidgetRenderer.hpp>
+#include <TGUI/String.hpp>
+
+#include <map>
+#include <memory>
+
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+namespace tgui
+{
+    class Theme;
+
+    /// Fallback renderers from Theme.\<Alias\> sections in the form file
+    using ThemeFallbackMap = std::map<String, std::map<String, std::shared_ptr<RendererData>>>;
+
+    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    /// @internal
+    /// @brief Resources used when loading widgets from a form file
+    /////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+    struct TGUI_API WidgetLoadResources
+    {
+        const std::map<String, std::shared_ptr<RendererData>>& renderers;
+        const std::map<String, std::shared_ptr<Theme>>* runtimeThemesByAlias = nullptr;
+        const ThemeFallbackMap* themeFallbacks = nullptr;
+
+        explicit WidgetLoadResources(const std::map<String, std::shared_ptr<RendererData>>& r) :
+            renderers(r)
+        {
+        }
+    };
+} // namespace tgui
+
+/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
+
+#endif // TGUI_WIDGET_LOAD_RESOURCES_HPP