Can't load font from memory if FontDataOwnedByAtlas=true

[gucio321]

Hi
Sorry If my question is stupid, but I have read everything in FONTS.md and can't see answer 😕
Here is what you need to reproduce:

diff --git a/examples/example_glfw_opengl3/main.cpp b/examples/example_glfw_opengl3/main.cpp
index 212c7fb1a..40523ba30 100644
--- a/examples/example_glfw_opengl3/main.cpp
+++ b/examples/example_glfw_opengl3/main.cpp
@@ -8,6 +8,7 @@
 // - Introduction, links and more at the top of imgui.cpp
 
 #include "imgui.h"
+#include "imgui_internal.h"
 #include "imgui_impl_glfw.h"
 #include "imgui_impl_opengl3.h"
 #include <stdio.h>
@@ -97,7 +98,11 @@ int main(int, char**)
     // - Our Emscripten build process allows embedding fonts to be accessible at runtime from the "fonts/" folder. See Makefile.emscripten for details.
     //io.Fonts->AddFontDefault();
     //io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\segoeui.ttf", 18.0f);
-    //io.Fonts->AddFontFromFileTTF("../../misc/fonts/DroidSans.ttf", 16.0f);
+    size_t data_size = 0;
+    void* data = ImFileLoadToMemory("../../misc/fonts/DroidSans.ttf", "rb", &data_size, 0);
+    ImFontConfig cfg;
+    cfg.FontDataOwnedByAtlas = false;
+    io.Fonts->AddFontFromMemoryTTF(data, 16.0f,16.0f, &cfg);
     //io.Fonts->AddFontFromFileTTF("../../misc/fonts/Roboto-Medium.ttf", 16.0f);
     //io.Fonts->AddFontFromFileTTF("../../misc/fonts/Cousine-Regular.ttf", 15.0f);
     //ImFont* font = io.Fonts->AddFontFromFileTTF("c:\\Windows\\Fonts\\ArialUni.ttf", 18.0f, nullptr, io.Fonts->GetGlyphRangesJapanese());

(Its just ~copy-paste of what imgui_draw.cpp AddFontFromMemoryTTF does but with config.FontDataOwnedByAtlas set to false)
and demo crashes with message:

kNewFrameSanityChecks(): Assertion `g.IO.Fonts->IsBuilt() && "Font Atlas not built! Make sure you called ImGui_ImplXXXX_NewFrame() function for renderer backend, which should call io.Fonts->GetTexDataAsRGBA32() / GetTexDataAsAlpha8()"' failed.
Aborted (core dumped)

[ocornut]

Compiling I guess:

io.Fonts->AddFontFromMemoryTTF(data, 16.0f, 16.0f, &cfg);
main.cpp(83): warning C4244: 'argument': conversion from 'float' to 'int', possible loss of data

Your second parameter is wrong.

It should be:
io.Fonts->AddFontFromMemoryTTF(data, data_type,16.0f, &cfg);

Because of this the font fails to load.

[ocornut]

I have pushed a change 32171a8 to better detect this user mistake. Renamed parameters, and added better asserts.

[gucio321]

It worked, thank you!