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 };