Font stack cannot be manipulated within different windows

[wolfpld]

Version: 03ea87ea28
Branch: docking

Required setup:

io.Fonts->AddFontFromFileTTF("../../misc/fonts/ProggyTiny.ttf", 10.0f);   // will be used as default
ImFont* font = io.Fonts->AddFontFromFileTTF("../../misc/fonts/Roboto-Medium.ttf", 16.0f);

Test code:

ImGui::PushFont( font );
ImGui::Begin( "test" );
if( ImGui::Button( "click me" ) ) ImGui::OpenPopup( "popup" );
if( ImGui::BeginPopup( "popup" ) )
{
    ImGui::PopFont();
    ImGui::Text( "popup" );
    ImGui::PushFont( font );
    ImGui::EndPopup();
}
ImGui::End();
ImGui::PopFont();

This will display a window using a custom font (font), with the intention to display popup contents using the default one. This doesn't happen, as AddText() crashes in assert at imgui_draw.cpp:1228 (due to _TextureIdStack being empty).

[ocornut]

I confirmed this is an issue, we haven't looked at how the font stack was handled in a long while (it's not even exposing the (ugly form of) scaling).

Those functions PushFont/PopFont are currently mixing up context and per-window stacks:

g.FontStack.push_back(font);
g.CurrentWindow->DrawList->PushTextureID(font->ContainerAtlas->TexID);

g.CurrentWindow->DrawList->PopTextureID();
g.FontStack.pop_back();

(The irony being that all those TextureId are going to be the same since your atlas is the same)

As as quick workaround this will work if you don't need a title bar, which popups don't have:

ImGui::PushFont(font2);
ImGui::Begin("test");
if (ImGui::Button("click me"))
    ImGui::OpenPopup("popup");
if (ImGui::BeginPopup("popup"))
{
    ImGui::PushFont(font1);
    ImGui::Text("popup");
    ImGui::PopFont();
    ImGui::EndPopup();
}
ImGui::End();
ImGui::PopFont();

Will be looking for the proper fix.

[ocornut]

Amend: actually this is the proper workaround which will also work with title bars:

ImGui::PushFont(font2);
ImGui::Begin("test");
if (ImGui::Button("click me"))
    ImGui::OpenPopup("popup");

if (ImGui::IsPopupOpen("popup"))
{
    ImGui::PushFont(font1);
    if (ImGui::BeginPopup("popup"))
    {
        ImGui::Text("popup");
        ImGui::EndPopup();
    }
    ImGui::PopFont();
}

ImGui::End();
ImGui::PopFont();

Question: was this popup example you posted representative of your actual issue? Trying to gauge if the workaround can unblock you for a while or if there is some need to find a more generic solution soon.

[wolfpld]

Yes -- wolfpld/tracy@e330b96. Since a workaround exists, it's not a pressing issue.

(I use fixed width font to display source/asm code, but I do need to occasionally jump back to default font with icons, etc.)

[ocornut]

I have pushed a fix for this: eb7201b

(It's not a perfect fix, in theory our code and system are still rather broken for the case of using multiple atlases textures, but I don't think that has been fully exercised ever, so we'll address that when the time comes.)