AccessViolationException when loading multiple font sizes from memory

[ConradoDev]

I'm experiencing a System.AccessViolationException when loading fonts into ImGui.NET from memory. I load multiple font sizes of the same font (e.g., Bahnschrift size 16, 20, 24, etc.) without storing any font files on disk.

The error happens sporadically when calling ImFontAtlas_GetTexDataAsRGBA32, suggesting a possible memory corruption issue. It does not always occur but happens often enough to be a major problem.

Example code of LoadFonts() method

var bahnschrift = ReadStreamToByteArray(Variables.ResourcesFile.OpenChunk(0xac7ab5cc56086cfc));
using (var bahnschriftStream = new MemoryStream(bahnschrift))
{
    // Bahnschrift 16
    Bahnschrift16 = overlayInst.AddFontFromCRDO(bahnschriftStream, 16, FontGlyphRangeType.English, glyph_ranges_lang);

    // Bahnschrift 20
    ResetStream(bahnschriftStream);
    Bahnschrift20 = overlayInst.AddFontFromCRDO(bahnschriftStream, 20, FontGlyphRangeType.English, glyph_ranges_lang);

    // Bahnschrift 24
    ResetStream(bahnschriftStream);
    Bahnschrift24 = overlayInst.AddFontFromCRDO(bahnschriftStream, 24, FontGlyphRangeType.English, glyph_ranges_lang);

    // Bahnschrift 30
    ResetStream(bahnschriftStream);
    Bahnschrift30 = overlayInst.AddFontFromCRDO(bahnschriftStream, 30, FontGlyphRangeType.English, glyph_ranges_lang);

    // Bahnschrift 36
    ResetStream(bahnschriftStream);
    Bahnschrift36 = overlayInst.AddFontFromCRDO(bahnschriftStream, 36, FontGlyphRangeType.English, glyph_ranges_lang);
}

ResetStream() simply sets stream.Position = 0; to allow reusing the same stream for different font sizes.

public ImFontPtr AddFontFromCRDO(Stream stream, int size, FontGlyphRangeType language, ushort[]? customGlyphRange = null, bool merge = false)
{
    this.replaceFont = false;
    return this._Renderer.UpdateFontFromCRDO(stream, size, customGlyphRange, language, merge);
}

public unsafe ImFontPtr UpdateFontFromCRDO(Stream stream, float fontSize, ushort[]? fontCustomGlyphRange, FontGlyphRangeType fontLanguage, bool merge)
{
    var io = ImGui.GetIO();
    ImFontPtr ptr;

    this.DeRegisterTexture(io.Fonts.TexID)?.Dispose();

    var nativeConfig = ImGuiNative.ImFontConfig_ImFontConfig();
    var config = new ImFontConfigPtr(nativeConfig);

    config.MergeMode = merge;
    var pointer = AddFontFromCRDOTTF(stream, out int length);
    if (fontCustomGlyphRange == null)
    {
        ptr = io.Fonts.AddFontFromMemoryTTF(pointer, length, fontSize, config, GetGlyphRange(io, fontLanguage));
    }
    else
    {
        fixed (ushort* p = &fontCustomGlyphRange[0])
        {
            ptr = io.Fonts.AddFontFromMemoryTTF(pointer, length, fontSize, config, new nint(p));
        }
    }

    CreateFontsTexture();
    ImGuiNative.ImFontConfig_destroy(config);

    return ptr;
}

public void CreateFontsTexture()
{
    var io = ImGui.GetIO();

    io.Fonts.GetTexDataAsRGBA32(out byte* pixels, out var width, out var height);

    var texDesc = new Texture2DDescription(Format.R8G8B8A8_UNorm, width, height, 1, 1);
    var subResource = new SubresourceData(pixels, texDesc.Width * 4);
    using var texture = device.CreateTexture2D(texDesc, new[] { subResource });
    var resViewDesc = new ShaderResourceViewDescription(
        texture,
        ShaderResourceViewDimension.Texture2D,
        Format.R8G8B8A8_UNorm,
        0,
        texDesc.MipLevels);

    io.Fonts.SetTexID(RegisterTexture(device.CreateShaderResourceView(texture, resViewDesc)));
    io.Fonts.ClearTexData();
}

I have been struggling with this issue for a long time and haven't found a solution.