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FreeType: Fix CBDT/COLR bitmap color emoji font loading (#6302) #9483

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FreeType: Fix CBDT/COLR bitmap color emoji font loading (#6302) #9483

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47 changes: 40 additions & 7 deletions misc/freetype/imgui_freetype.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -7,6 +7,7 @@

// CHANGELOG
// (minor and older changes stripped away, please see git history for details)
// 2026/07/19: fixed loading CBDT/COLR bitmap color emoji fonts (NotoColorEmoji, Twemoji COLR) by detecting CBDT table and using FT_Select_Size() instead of FT_Request_Size(). (#6302) [@sakiodre]
// 2025/06/11: refactored for the new ImFontLoader architecture, and ImGuiBackendFlags_RendererHasTextures support.
// 2024/10/17: added plutosvg support for SVG Fonts (seems faster/better than lunasvg). Enable by using '#define IMGUI_ENABLE_FREETYPE_PLUTOSVG'. (#7927)
// 2023/11/13: added support for ImFontConfig::RasterizationDensity field for scaling render density without scaling metrics.
Expand Down Expand Up @@ -449,13 +450,45 @@ static bool ImGui_ImplFreeType_FontBakedInit(ImFontAtlas* atlas, ImFontConfig* s
// FT_Set_Pixel_Sizes() doesn't seem to get us the same result."
// (FT_Set_Pixel_Sizes() essentially calls FT_Request_Size() with FT_SIZE_REQUEST_TYPE_NOMINAL)
const float rasterizer_density = src->RasterizerDensity * baked->RasterizerDensity;
FT_Size_RequestRec req;
req.type = (bd_font_data->UserFlags & ImGuiFreeTypeLoaderFlags_Bitmap) ? FT_SIZE_REQUEST_TYPE_NOMINAL : FT_SIZE_REQUEST_TYPE_REAL_DIM;
req.width = 0;
req.height = (uint32_t)(size * 64 * rasterizer_density);
req.horiResolution = 0;
req.vertResolution = 0;
FT_Request_Size(bd_font_data->FtFace, &req);

// Detect CBDT/COLR bitmap fonts (NotoColorEmoji, Twemoji COLR, etc.) which are not scalable
// and require FT_Select_Size() instead of FT_Request_Size(). (#6302)
FT_ULong cbdt_tag = FT_MAKE_TAG('C', 'B', 'D', 'T');
FT_ULong cbdt_length = 0;
FT_Error cbdt_err = FT_Load_Sfnt_Table(bd_font_data->FtFace, cbdt_tag, 0, nullptr, &cbdt_length);
bool is_cbdt_font = (cbdt_err == 0 && cbdt_length > 0);

if (is_cbdt_font && bd_font_data->FtFace->num_fixed_sizes > 0)
{
// Select the closest available bitmap strike size
int best_match = 0;
FT_Int best_diff = INT_MAX;
FT_Int target_size = (FT_Int)(size * rasterizer_density);
for (int i = 0; i < bd_font_data->FtFace->num_fixed_sizes; i++)
{
FT_Int diff = (FT_Int)bd_font_data->FtFace->available_sizes[i].height - target_size;
if (diff < 0) diff = -diff;
if (diff < best_diff)
{
best_diff = diff;
best_match = i;
}
}
FT_Select_Size(bd_font_data->FtFace, best_match);
// Load color glyphs
bd_font_data->LoadFlags |= FT_LOAD_COLOR;
}
else
{
// Standard scalable font path
FT_Size_RequestRec req;
req.type = (bd_font_data->UserFlags & ImGuiFreeTypeLoaderFlags_Bitmap) ? FT_SIZE_REQUEST_TYPE_NOMINAL : FT_SIZE_REQUEST_TYPE_REAL_DIM;
req.width = 0;
req.height = (uint32_t)(size * 64 * rasterizer_density);
req.horiResolution = 0;
req.vertResolution = 0;
FT_Request_Size(bd_font_data->FtFace, &req);
}

// Output
if (src->MergeMode == false)
Expand Down
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