Avoid switching a built legacy font atlas to managed textures

[martinecker]

When NetImgui connects after a legacy renderer has built the font atlas, keep RendererHasTextures disabled. Dear ImGui does not allow this setting to change after the atlas is built. Continue sending the retained atlas pixels to the server so remote rendering still receives the font texture.

[sammyfreg]

Did you encounter an issue where you have a backend renderer that do not support the new imgui texture updates, and then connected to net imgui after the font was init by your backend, leading to issues?

[martinecker]

Yes, that was exactly it. Our game renderer doesn't yet support the new texture updates (working on fixing that). So it built and uploaded our font atlas before NetImgui connected and then the already-built font atlas was switched to managed textures, which triggered this assertion in imgui_draw.cpp:

    if (atlas->TexIsBuilt && atlas->Builder->PreloadedAllGlyphsRanges)
        IM_ASSERT_USER_ERROR(atlas->RendererHasTextures == false, "Called ImFontAtlas::Build() before ImGuiBackendFlags_RendererHasTextures got set! With new backends: you don't need to call Build().");

[sammyfreg]

Thanks, it will repro it on my side and decides if I should take your changes as is, or add support for font un-init when connecting and then restore the previous atlas on disconnect.

…

On Sat, Sep 5, 2026, 11:47 a.m. Martin Ecker ***@***.***> wrote: *martinecker* left a comment (sammyfreg/netImgui#74) <#74 (comment)> Yes, that was exactly it. Our game renderer doesn't yet support the new texture updates (working on fixing that). So it built and uploaded our font atlas before NetImgui connected and then the already-built font atlas was switched to managed textures, which triggered this assertion in imgui_draw.cpp: if (atlas->TexIsBuilt && atlas->Builder->PreloadedAllGlyphsRanges) IM_ASSERT_USER_ERROR(atlas->RendererHasTextures == false, "Called ImFontAtlas::Build() before ImGuiBackendFlags_RendererHasTextures got set! With new backends: you don't need to call Build()."); — Reply to this email directly, view it on GitHub <#74?email_source=notifications&email_token=AESBPY5V3ZYSZU26JH6FWDL5NQYQ7A5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKNJVGI4TGNJZGUZ2M4TFMFZW63VHMNXW23LFNZ2KKZLWMVXHJLDGN5XXIZLSL5RWY2LDNM#issuecomment-5552935953>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AESBPY5QERMVOHX6FIAUYI35NQYQ7AVCNFSNUABFKJSXA33TNF2G64TZHMZDMMJXGI2TEOBRHNEXG43VMU5TKMZVGEZDGMBZHA3KC5QC> . Triage notifications, keep track of coding agent tasks and review pull requests on the go with GitHub Mobile for iOS <https://github.com/notifications/mobile/ios/AESBPY5II7UERXPZAWVJXXD5NQYQ7A5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKNJVGI4TGNJZGUZ2M4TFMFZW63VHMNXW23LFNZ2KKZLWMVXHJKTGN5XXIZLSL5UW64Y> and Android <https://github.com/notifications/mobile/android/AESBPY26V5DZFKRIL5V3SC35NQYQ7A5CNFSNUABFM5UWIORPF5TWS5BNNB2WEL2JONZXKZKDN5WW2ZLOOQXTKNJVGI4TGNJZGUZ2M4TFMFZW63VHMNXW23LFNZ2KKZLWMVXHJLTGN5XXIZLSL5QW4ZDSN5UWI>. Download it today! You are receiving this because you commented.Message ID: ***@***.***>

[sammyfreg]

Decided to keep this change as is (minus the fix to make it work in the dev branch). I was planning to duplicate the font atlas, but it's not worth adding complexity to handle texture support when not supported by native backend.