callbacks.LoadAdditionalFonts can be re-used during execution

src/hello_imgui/doc_params.md

@@ -313,11 +313,10 @@ struct RunnerCallbacks
     void EnqueuePostInit(const VoidFunction& callback);
 
     // `LoadAdditionalFonts`: default=_LoadDefaultFont_WithFontAwesome*.
-    //  A function that is called once, when fonts are ready to be loaded.
-    //  By default, _LoadDefaultFont_WithFontAwesome_ is called,
-    //  but you can copy and customize it.
-    //  (LoadDefaultFont_WithFontAwesome will load fonts from assets/fonts/
-    //  but reverts to the ImGui embedded font if not found)
+    //  A function that is called in order to load fonts.
+    // `LoadAdditionalFonts` will be called once, then *set to nullptr*.
+    // If you want to load additional fonts, during the app execution, you can
+    // set LoadAdditionalFonts to a function that will load the additional fonts.
     VoidFunction LoadAdditionalFonts = (VoidFunction)ImGuiDefaultSettings::LoadDefaultFont_WithFontAwesomeIcons;
     // If LoadAdditionalFonts==LoadDefaultFont_WithFontAwesomeIcons, this parameter control
     // which icon font will be loaded by default.
@@ -361,7 +360,7 @@ struct RunnerCallbacks
 
     // `PreNewFrame`: You can here add a function that will be called at each frame,
     //  and before the call to ImGui::NewFrame().
-    //  It is a good place to dynamically add new fonts, or new dockable windows.
+    //  It is a good place to add new dockable windows.
     VoidFunction PreNewFrame = EmptyVoidFunction();
 
     // `BeforeImGuiRender`: You can here add a function that will be called at each frame,

src/hello_imgui/internal/backend_impls/abstract_runner.cpp

@@ -61,12 +61,18 @@
 //
 
 
+
 namespace HelloImGui
 {
 // Encapsulated inside hello_imgui_screenshot.cpp
 void setFinalAppWindowScreenshotRgbBuffer(const ImageBuffer& b);
 
 
+// Only used with OpenGL if the font loading failed at first frame
+// (used by ReloadFontIfFailed_OpenGL(), which should ideally by suppressed)
+VoidFunction gInitialFontLoadingFunction = nullptr;
+
+
 AbstractRunner::AbstractRunner(RunnerParams &params_)
     : params(params_) {}
 
@@ -76,19 +82,19 @@ AbstractRunner::AbstractRunner(RunnerParams &params_)
 // size for a crisper rendering) and try to reload the fonts.
 // This only works if the user provided callback LoadAdditionalFonts() uses DpiFontLoadingFactor()
 // to multiply its font size.
-void AbstractRunner::ReloadFontIfFailed() const
+void AbstractRunner::ReloadFontIfFailed_OpenGL() const
 {
     fprintf(stderr, "Detected a potential font loading error! You might try to reduce the number of loaded fonts and/or their size!\n");
 #ifdef HELLOIMGUI_HAS_OPENGL
-    if (ImGui::GetIO().FontGlobalScale < 1.f)
+    if (ImGui::GetIO().FontGlobalScale < 1.f && gInitialFontLoadingFunction)
     {
         fprintf(stderr,
                 "Trying to solve the font loading error by changing ImGui::GetIO().FontGlobalScale from %f to 1.f! Font rendering might be less crisp...\n",
                 ImGui::GetIO().FontGlobalScale
                 );
         ImGui::GetIO().FontGlobalScale = 1.f;
         ImGui::GetIO().Fonts->Clear();
-        params.callbacks.LoadAdditionalFonts();
+        gInitialFontLoadingFunction();
         ImGui::GetIO().Fonts->Build();
         ImGui_ImplOpenGL3_CreateFontsTexture();
     }
@@ -662,10 +668,13 @@ void AbstractRunner::Setup()
     //
     // load fonts & set ImGui::GetIO().FontGlobalScale
     //
-    ImGui::GetIO().Fonts->Clear();
+
     // LoadAdditionalFonts will load fonts and resize them by 1./FontGlobalScale
     // (if and only if it uses HelloImGui::LoadFontTTF instead of ImGui's font loading functions)
+    ImGui::GetIO().Fonts->Clear();
+    gInitialFontLoadingFunction = params.callbacks.LoadAdditionalFonts;
     params.callbacks.LoadAdditionalFonts();
+    params.callbacks.LoadAdditionalFonts = nullptr;
     bool buildSuccess = ImGui::GetIO().Fonts->Build();
     IM_ASSERT(buildSuccess && "ImGui::GetIO().Fonts->Build() failed!");
     {
@@ -905,6 +914,19 @@ void AbstractRunner::CreateFramesAndRender()
         #endif
     } // SCOPED_RELEASE_GIL_ON_MAIN_THREAD end
 
+    if (true_gil) // Load additional fonts during execution
+    {
+        if (params.callbacks.LoadAdditionalFonts != nullptr)
+        {
+            params.callbacks.LoadAdditionalFonts();
+            ImGui::GetIO().Fonts->Build();
+            // cf https://github.com/ocornut/imgui/issues/6547
+            // We need to recreate the rendering backend device objects
+            mRenderingBackendCallbacks->Impl_DestroyFontTexture();
+            mRenderingBackendCallbacks->Impl_CreateFontTexture();
+            params.callbacks.LoadAdditionalFonts = nullptr;
+        }
+    }
 
     //
     // Rendering logic
@@ -950,7 +972,10 @@ void AbstractRunner::CreateFramesAndRender()
             {
                 auto error = glGetError();
                 if (error != 0)
+                {
+                    fprintf(stderr, "OpenGL error detected on first frame: %d. Will try to reload font without scaling\n", error);
                     foundPotentialFontLoadingError = true;
+                }
             }
         }
         #endif
@@ -997,7 +1022,7 @@ void AbstractRunner::CreateFramesAndRender()
     #endif
 
     if (foundPotentialFontLoadingError)
-        ReloadFontIfFailed();
+        ReloadFontIfFailed_OpenGL();
 
     mIdxFrame += 1;
 }

src/hello_imgui/internal/backend_impls/abstract_runner.h

@@ -85,7 +85,7 @@ class AbstractRunner
     void SetupDpiAwareParams();
     void PrepareWindowGeometry();
     void HandleDpiOnSecondFrame();
-    void ReloadFontIfFailed() const;
+    void ReloadFontIfFailed_OpenGL() const;
     void MakeWindowSizeRelativeTo96Ppi_IfRequired();
     bool ShallSizeWindowRelativeTo96Ppi();
     bool WantAutoSize();

src/hello_imgui/internal/backend_impls/rendering_callbacks.h

@@ -98,6 +98,9 @@ namespace HelloImGui
         VoidFunction                  Impl_Shutdown_3D          = [] { HIMG_ERROR("Empty function"); };
         std::function<ImageBuffer()>  Impl_ScreenshotRgb_3D     = [] { return ImageBuffer{}; };
         std::function<ScreenSize()>   Impl_GetFrameBufferSize;   //= [] { return ScreenSize{0, 0}; };
+
+        VoidFunction                  Impl_DestroyFontTexture  = [] { HIMG_ERROR("Empty function"); };
+        VoidFunction                  Impl_CreateFontTexture   = [] { HIMG_ERROR("Empty function"); };
     };
 
     using RenderingCallbacksPtr = std::shared_ptr<RenderingCallbacks>;

src/hello_imgui/internal/backend_impls/rendering_dx11.cpp

@@ -131,6 +131,9 @@ namespace HelloImGui
 
         //         callbacks->Impl_GetFrameBufferSize;   //= [] { return ScreenSize{0, 0}; };
 
+        callbacks->Impl_CreateFontTexture = ImGui_ImplDX11_CreateFontsTexture;
+        callbacks->Impl_DestroyFontTexture = ImGui_ImplDX11_DestroyFontsTexture;
+
         return callbacks;
     }
 

src/hello_imgui/internal/backend_impls/rendering_dx12.cpp

@@ -312,6 +312,9 @@ namespace HelloImGui
         // callbacks->Impl_ScreenshotRgb_3D     = [] { return ImageBuffer{}; };
         // callbacks->Impl_GetFrameBufferSize;   //= [] { return ScreenSize{0, 0}; };
 
+        callbacks->Impl_CreateFontTexture = ImGui_ImplDX12_CreateFontsTexture;
+        callbacks->Impl_DestroyFontTexture = ImGui_ImplDX12_DestroyFontsTexture;
+
 
         return callbacks;
     }

src/hello_imgui/internal/backend_impls/rendering_metal.mm

@@ -102,6 +102,13 @@ RenderingCallbacksPtr PrepareBackendCallbacksCommon()
             ImGui_ImplMetal_Shutdown();
         };
 
+        callbacks->Impl_CreateFontTexture = []
+        {
+            auto& gMetalGlobals = GetMetalGlobals();
+            ImGui_ImplMetal_CreateFontsTexture(gMetalGlobals.mtlDevice);
+        };
+        callbacks->Impl_DestroyFontTexture = ImGui_ImplMetal_DestroyFontsTexture;
+
         return callbacks;
     }
 

src/hello_imgui/internal/backend_impls/rendering_opengl3.cpp

@@ -34,6 +34,9 @@ namespace HelloImGui
             ImGui_ImplOpenGL3_Shutdown();
         };
 
+        callbacks->Impl_CreateFontTexture = ImGui_ImplOpenGL3_CreateFontsTexture;
+        callbacks->Impl_DestroyFontTexture = ImGui_ImplOpenGL3_DestroyFontsTexture;
+
         return callbacks;
     }
 

src/hello_imgui/internal/backend_impls/rendering_vulkan.cpp

@@ -102,6 +102,9 @@ namespace HelloImGui
         // callbacks->Impl_ScreenshotRgb_3D     = [] { return ImageBuffer{}; };
         // callbacks->Impl_GetFrameBufferSize;   //= [] { return ScreenSize{0, 0}; };
 
+        callbacks->Impl_CreateFontTexture = ImGui_ImplVulkan_CreateFontsTexture;
+        callbacks->Impl_DestroyFontTexture = ImGui_ImplVulkan_DestroyFontsTexture;
+
 
         return callbacks;
     }

src/hello_imgui/runner_callbacks.h

@@ -183,11 +183,10 @@ struct RunnerCallbacks
     void EnqueuePostInit(const VoidFunction& callback);
 
     // `LoadAdditionalFonts`: default=_LoadDefaultFont_WithFontAwesome*.
-    //  A function that is called once, when fonts are ready to be loaded.
-    //  By default, _LoadDefaultFont_WithFontAwesome_ is called,
-    //  but you can copy and customize it.
-    //  (LoadDefaultFont_WithFontAwesome will load fonts from assets/fonts/
-    //  but reverts to the ImGui embedded font if not found)
+    //  A function that is called in order to load fonts.
+    // `LoadAdditionalFonts` will be called once, then *set to nullptr*.
+    // If you want to load additional fonts, during the app execution, you can
+    // set LoadAdditionalFonts to a function that will load the additional fonts.
     VoidFunction LoadAdditionalFonts = (VoidFunction)ImGuiDefaultSettings::LoadDefaultFont_WithFontAwesomeIcons;
     // If LoadAdditionalFonts==LoadDefaultFont_WithFontAwesomeIcons, this parameter control
     // which icon font will be loaded by default.
@@ -231,7 +230,7 @@ struct RunnerCallbacks
 
     // `PreNewFrame`: You can here add a function that will be called at each frame,
     //  and before the call to ImGui::NewFrame().
-    //  It is a good place to dynamically add new fonts, or new dockable windows.
+    //  It is a good place to add new dockable windows.
     VoidFunction PreNewFrame = EmptyVoidFunction();
 
     // `BeforeImGuiRender`: You can here add a function that will be called at each frame,