Loading Font Icons to Use with ImGui

[blacktorch]

I am trying to use font awesome icons, but my app crashes. I am using rocky with QT. I do not know if I am loading it in the proper place. Thanks.

ImGuiIO& io = ImGui::GetIO();
ImFontConfig config;
config.PixelSnapH = true;
static const ImWchar icon_ranges[] = { 0xe005, 0xf8ff, 0 };
ImFont* ft = io.Fonts->AddFontFromFileTTF("fa-solid-900.ttf", 13.0f, &config, icon_ranges);
auto [lock, registry] = app.registry.write();

entity = registry.create();

auto& widget = registry.emplace<Widget>(entity);
widget.text = "Mission Parameters";

widget.render = [&](WidgetInstance& i)
{

    static float some_float = 0;
    static int some_int = 0;
    static bool fixed_window_open = false;

    static ImVec4 color1 = ImVec4(1.0f, 0.0f, 0.0f, 1.0f);

    i.begin();
    i.windowFlags &= ~ImGuiWindowFlags_NoInputs;
    i.windowFlags &= ~ImGuiWindowFlags_NoBringToFrontOnFocus;

    ImGui::PushStyleVar(ImGuiStyleVar_WindowRounding, 15.0f);
    ImGui::SetNextWindowBgAlpha(1.0f);

    i.render([&]()
             {
                 ImGui::Text(i.widget.text.c_str());
                 ImGui::Separator();

                 ImGui::PushFont(ft);
                 ImGui::Text(ICON_FA_ADDRESS_BOOK);

                 if (ImGui::Button(ICON_FA_ARROW_DOWN_A_Z))
                 {
                     // Action for button 1
                     printf("Button 1 clicked!\n");
                 }
                ImGui::PopFont();
                 // Edit a color stored as 4 floats
                 ImGui::ColorEdit4("##Color1", (float*)&color1, ImGuiColorEditFlags_NoInputs);
                 ImGui::Checkbox("Show me a fixed-position window", &fixed_window_open);
             });

    ImGui::PopStyleVar();

    i.end();
};

// Attach a transform to place and move the label:
auto& transform = registry.emplace<Transform>(entity);
transform.position = GeoPoint(SRS::WGS84, -25.0, 25.0, 2'500'000.0);
transform.topocentric = true;

// Drop line from the widget to the ground, for fun.
auto& dropline = registry.emplace<Line>(entity);
dropline.points = { { 0,0,0 }, { 0, 0, -2'500'000.0 } };
dropline.style.color = Color(0.1f, 0.1f, 0.1f, 1.0f);
dropline.style.width = 2;

[gwaldron]

I have not done much with ImGui fonts. Suggest you read the Fonts FAQ and see if there are any hints. You may have to call Build()?

[blacktorch]

I guess my problem is where to do the whole font setup. If I do my setup which includes calling the Build() function before the widget.render function, the program crashes (ft seems to be null within the lambda function). If I do it after calling i.begin() which sets the context, the program runs but just stays frozen and nothing works. I guess it is because the render function is called multiple times and building of the Font atlas takes up a lot of resources and shouldn't be happening in every render cycle.

[gwaldron]

The good news is that ImGui has a NEW dynamic font system, as of version 1.92.0 (https://github.com/ocornut/imgui/releases/tag/v1.92.0)

The bad news is that 1.92.0 is not yet in vcpkg :)

[blacktorch]

Thanks I did see that, but I think I will still have the issue of the proper place to call

ImGuiIO& io = ImGui::GetIO();
io.Fonts->AddFontDefault();
...
and perform the rest of my setup for the using fonts as stated in ImGui docs.

If I do it before ImGui::SetCurrentContext(context); is called ( this happens in i.begin() ), it crashes, if I do it after that, the entire setup will happen every time the widget.render function is called which freezes the app. Is it possible to set the context elsewhere and pass it to widget.render? So my Font setup only happens once. Thanks.

[gwaldron]

The reason it is not possible to call SetCurrentContext elsewhere is because the ImGui current context pointer is a global static, and is therefore not shared across DLL boundaries. So setting it in the rocky DLL will not set it in your application (on Windows, anyway). This is very annoying but it is why we have i.begin() and i.end(). I'm open to other/better ideas for how to tackle this!

[blacktorch]

I solved the problem by calling ImGui_ImplVulkan_CreateFontsTexture(); after adding the font. Didn't even need to call Build.

[ComradeMashkov]

Hey, @blacktorch, basically how did you manage to load a font? It was working for me until I've updated to 0.9.0 version and now when I call GetIO() after RenderImGuiContext::create(window) and then load my fonts with ImGui_ImplVulkan_CreateFontsTexture(), the program crashes...

[ComradeMashkov]

Ok, so a little update coming from my experience. I've just pushed ImGui::SetCurrentContext(imguiRenderer->imguiContext()); right after auto imguiRenderer = rocky::RenderImGuiContext::create(window); and now everything is just fine.