zed-industries/zed · error · windows::core::Error

DWRITE_E_UNSUPPORTEDOPERATION

DWRITE_E_UNSUPPORTEDOPERATION

Error message

Failed to cast font face

What it means

In the DirectWrite glyph-run renderer, the cached font face could not be cast to IDWriteFontFace3. The renderer returns DWRITE_E_UNSUPPORTEDOPERATION so callers can take a fallback path for this glyph run.

Source

Thrown at crates/gpui_windows/src/direct_write.rs:1494

        _measuringmode: DWRITE_MEASURING_MODE,
        glyphrun: *const DWRITE_GLYPH_RUN,
        glyphrundescription: *const DWRITE_GLYPH_RUN_DESCRIPTION,
        _clientdrawingeffect: windows::core::Ref<windows::core::IUnknown>,
    ) -> windows::core::Result<()> {
        let glyphrun = unsafe { &*glyphrun };
        let glyph_count = glyphrun.glyphCount as usize;
        if glyph_count == 0 {
            return Ok(());
        }
        let desc = unsafe { &*glyphrundescription };
        let context = unsafe { &mut *(clientdrawingcontext.cast::<RendererContext>().cast_mut()) };
        let Some(font_face) = glyphrun.fontFace.as_ref() else {
            return Ok(());
        };
        // This `cast()` action here should never fail since we are running on Win10+, and
        // `IDWriteFontFace3` requires Win10
        let Ok(font_face) = &font_face.cast::<IDWriteFontFace3>() else {
            return Err(Error::new(
                DWRITE_E_UNSUPPORTEDOPERATION,
                "Failed to cast font face",
            ));
        };

        let font_face_key = font_face.cast::<IUnknown>().unwrap().as_raw().addr();
        let font_id = context
            .text_system
            .font_info_cache
            .get(&font_face_key)
            .copied()
            // in some circumstances, we might be getting served a FontFace that we did not create ourselves
            // so create a new font from it and cache it accordingly. The usual culprit here seems to be Segoe UI Symbol
            .map_or_else(
                || {
                    let font = font_face_to_font(font_face, &self.locale)
                        .ok_or_else(|| Error::new(DWRITE_E_NOFONT, "Failed to create font"))?;
                    let font_id = match context.text_system.font_to_font_id.get(&font) {

View on GitHub (pinned to f4178619ac)

Solutions

1. Let the caller fall back to a simpler rendering path on unsupported-operation
2. Ensure the font face was created via an API that yields IDWriteFontFace3 (older/custom font sources may only provide earlier interfaces)

When it happens

Trigger: Thrown at crates/gpui_windows/src/direct_write.rs:1494 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of zed-industries/zed@f4178619ac (2026-08-20). Data as JSON: /api/errors/c70ad59c6cd6b7f4. Report an issue: GitHub.