Fonts: Fix calling ClearTexData() (clearing CPU side font data) triggering an assert in NewFrame(). (#3487) + Backends: added additional assert to facilitate detecting user understand they haven't initialized a backend.

backends/imgui_impl_allegro5.cpp

@@ -430,6 +430,8 @@ static void ImGui_ImplAllegro5_UpdateMouseCursor()
 void ImGui_ImplAllegro5_NewFrame()
 {
     ImGui_ImplAllegro5_Data* bd = ImGui_ImplAllegro5_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplAllegro5_Init()?");
+
     if (!bd->Texture)
         ImGui_ImplAllegro5_CreateDeviceObjects();
 

backends/imgui_impl_dx10.cpp

@@ -563,6 +563,8 @@ void ImGui_ImplDX10_Shutdown()
 void ImGui_ImplDX10_NewFrame()
 {
     ImGui_ImplDX10_Data* bd = ImGui_ImplDX10_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplDX10_Init()?");
+
     if (!bd->pFontSampler)
         ImGui_ImplDX10_CreateDeviceObjects();
 }

backends/imgui_impl_dx11.cpp

@@ -579,6 +579,8 @@ void ImGui_ImplDX11_Shutdown()
 void ImGui_ImplDX11_NewFrame()
 {
     ImGui_ImplDX11_Data* bd = ImGui_ImplDX11_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplDX11_Init()?");
+
     if (!bd->pFontSampler)
         ImGui_ImplDX11_CreateDeviceObjects();
 }

backends/imgui_impl_dx12.cpp

@@ -733,6 +733,8 @@ void ImGui_ImplDX12_Shutdown()
 void ImGui_ImplDX12_NewFrame()
 {
     ImGui_ImplDX12_Data* bd = ImGui_ImplDX12_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplDX12_Init()?");
+
     if (!bd->pPipelineState)
         ImGui_ImplDX12_CreateDeviceObjects();
 }

backends/imgui_impl_dx9.cpp

@@ -362,6 +362,8 @@ void ImGui_ImplDX9_InvalidateDeviceObjects()
 void ImGui_ImplDX9_NewFrame()
 {
     ImGui_ImplDX9_Data* bd = ImGui_ImplDX9_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplDX9_Init()?");
+
     if (!bd->FontTexture)
         ImGui_ImplDX9_CreateDeviceObjects();
 }

backends/imgui_impl_glfw.cpp

@@ -384,6 +384,7 @@ void ImGui_ImplGlfw_NewFrame()
 {
     ImGuiIO& io = ImGui::GetIO();
     ImGui_ImplGlfw_Data* bd = ImGui_ImplGlfw_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplGlfw_InitForXXX()?");
 
     // Setup display size (every frame to accommodate for window resizing)
     int w, h;

backends/imgui_impl_opengl2.cpp

@@ -96,6 +96,8 @@ void    ImGui_ImplOpenGL2_Shutdown()
 void    ImGui_ImplOpenGL2_NewFrame()
 {
     ImGui_ImplOpenGL2_Data* bd = ImGui_ImplOpenGL2_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplOpenGL2_Init()?");
+
     if (!bd->FontTexture)
         ImGui_ImplOpenGL2_CreateDeviceObjects();
 }

backends/imgui_impl_opengl3.cpp

@@ -305,6 +305,8 @@ void    ImGui_ImplOpenGL3_Shutdown()
 void    ImGui_ImplOpenGL3_NewFrame()
 {
     ImGui_ImplOpenGL3_Data* bd = ImGui_ImplOpenGL3_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplOpenGL3_Init()?");
+
     if (!bd->ShaderHandle)
         ImGui_ImplOpenGL3_CreateDeviceObjects();
 }

backends/imgui_impl_sdl.cpp

@@ -381,6 +381,7 @@ void ImGui_ImplSDL2_NewFrame(SDL_Window* window)
 {
     ImGuiIO& io = ImGui::GetIO();
     ImGui_ImplSDL2_Data* bd = ImGui_ImplSDL2_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplSDL2_Init()?");
     IM_ASSERT(bd->Window == window); // FIXME: Should remove parameter from ImGui_ImplSDL2_NewFrame()
 
     // Setup display size (every frame to accommodate for window resizing)

backends/imgui_impl_vulkan.cpp

@@ -1060,6 +1060,9 @@ void ImGui_ImplVulkan_Shutdown()
 
 void ImGui_ImplVulkan_NewFrame()
 {
+    ImGui_ImplVulkan_Data* bd = ImGui_ImplVulkan_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplVulkan_Init()?");
+    IM_UNUSED(bd);
 }
 
 void ImGui_ImplVulkan_SetMinImageCount(uint32_t min_image_count)

backends/imgui_impl_win32.cpp

@@ -289,6 +289,7 @@ void    ImGui_ImplWin32_NewFrame()
 {
     ImGuiIO& io = ImGui::GetIO();
     ImGui_ImplWin32_Data* bd = ImGui_ImplWin32_GetBackendData();
+    IM_ASSERT(bd != NULL && "Did you call ImGui_ImplWin32_Init()?");
 
     // Setup display size (every frame to accommodate for window resizing)
     RECT rect = { 0, 0, 0, 0 };

docs/CHANGELOG.txt

@@ -52,6 +52,7 @@ Other Changes:
 - Fonts: Prefer using U+FFFD character for fallback instead of '?', if available. (#4269)
 - Fonts: Use U+FF0E dot character to construct an ellipsis if U+002E '.' is not available. (#4269)
 - Fonts: Add U+FFFD ("replacement character") to default asian glyphs ranges. (#4269)
+- Fonts: Fix calling ClearTexData() (clearing CPU side font data) triggering an assert in NewFrame(). (#3487)
 - Demo: Fixed requirement in 1.83 to link with imgui_demo.cpp if IMGUI_DISABLE_METRICS_WINDOW is not set. (#4171)
   Normally the right way to disable compiling the demo is to set IMGUI_DISABLE_DEMO_WINDOWS, but we want to avoid
   implying that the file is required.

imgui.h

@@ -2627,7 +2627,7 @@ struct ImFontAtlas
     IMGUI_API bool              Build();                    // Build pixels data. This is called automatically for you by the GetTexData*** functions.
     IMGUI_API void              GetTexDataAsAlpha8(unsigned char** out_pixels, int* out_width, int* out_height, int* out_bytes_per_pixel = NULL);  // 1 byte per-pixel
     IMGUI_API void              GetTexDataAsRGBA32(unsigned char** out_pixels, int* out_width, int* out_height, int* out_bytes_per_pixel = NULL);  // 4 bytes-per-pixel
-    bool                        IsBuilt() const             { return Fonts.Size > 0 && (TexPixelsAlpha8 != NULL || TexPixelsRGBA32 != NULL); }
+    bool                        IsBuilt() const             { return Fonts.Size > 0 && TexReady; } // Bit ambiguous: used to detect when user didn't built texture but effectively we should check TexID != 0 except that would be backend dependent...
     void                        SetTexID(ImTextureID id)    { TexID = id; }
 
     //-------------------------------------------
@@ -2677,6 +2677,7 @@ struct ImFontAtlas
 
     // [Internal]
     // NB: Access texture data via GetTexData*() calls! Which will setup a default font for you.
+    bool                        TexReady;           // Set when texture was built matching current font input
     bool                        TexPixelsUseColors; // Tell whether our texture data is known to use colors (rather than just alpha channel), in order to help backend select a format.
     unsigned char*              TexPixelsAlpha8;    // 1 component per pixel, each component is unsigned 8-bit. Total size = TexWidth * TexHeight
     unsigned int*               TexPixelsRGBA32;    // 4 component per pixel, each component is unsigned 8-bit. Total size = TexWidth * TexHeight * 4

imgui_draw.cpp

@@ -2002,6 +2002,7 @@ void    ImFontAtlas::ClearInputData()
     ConfigData.clear();
     CustomRects.clear();
     PackIdMouseCursors = PackIdLines = -1;
+    TexReady = false;
 }
 
 void    ImFontAtlas::ClearTexData()
@@ -2014,12 +2015,14 @@ void    ImFontAtlas::ClearTexData()
     TexPixelsAlpha8 = NULL;
     TexPixelsRGBA32 = NULL;
     TexPixelsUseColors = false;
+    // Important: we leave TexReady untouched
 }
 
 void    ImFontAtlas::ClearFonts()
 {
     IM_ASSERT(!Locked && "Cannot modify a locked ImFontAtlas between NewFrame() and EndFrame/Render()!");
     Fonts.clear_delete();
+    TexReady = false;
 }
 
 void    ImFontAtlas::Clear()
@@ -2092,6 +2095,7 @@ ImFont* ImFontAtlas::AddFont(const ImFontConfig* font_cfg)
         new_font_cfg.DstFont->EllipsisChar = font_cfg->EllipsisChar;
 
     // Invalidate texture
+    TexReady = false;
     ClearTexData();
     return new_font_cfg.DstFont;
 }
@@ -2795,6 +2799,8 @@ void ImFontAtlasBuildFinish(ImFontAtlas* atlas)
     for (int i = 0; i < atlas->Fonts.Size; i++)
         if (atlas->Fonts[i]->DirtyLookupTables)
             atlas->Fonts[i]->BuildLookupTable();
+
+    atlas->TexReady = true;
 }
 
 // Retrieve list of range (2 int per range, values are inclusive)