No font fallback found. The software renderer requires enabl

Error message

No font fallback found. The software renderer requires enabling the `EmbedForSoftwareRenderer` option when compiling slint files.

What it means

Error "No font fallback found. The software renderer requires enabling the `EmbedForSoftwareRenderer` option when compiling slint files." thrown in slint-ui/slint.

Source

Thrown at internal/renderers/software/fonts.rs:193

                fonts
                    .iter()
                    .cloned()
                    .filter(|bitmap_font| bitmap_font.italic == request.italic)
                    .min_by_key(|bitmap_font| bitmap_font.weight.abs_diff(requested_weight))
                    .or_else(|| fonts.first().cloned())
            }) {
                fallback_bitmap_font
            } else {
                #[cfg(feature = "systemfonts")]
                return systemfonts::fallbackfont(
                    request,
                    scale_factor,
                    &mut font_context.collection,
                    &mut font_context.source_cache,
                )
                .into();
                #[cfg(not(feature = "systemfonts"))]
                panic!(
                    "No font fallback found. The software renderer requires enabling the `EmbedForSoftwareRenderer` option when compiling slint files."
                )
            }
        }
    };

    let requested_pixel_size: PhysicalLength =
        (request.pixel_size.unwrap_or(DEFAULT_FONT_SIZE).cast() * scale_factor).cast();

    let nearest_pixel_size = font
        .glyphs
        .partition_point(|glyphs| pixel_size(glyphs) <= requested_pixel_size)
        .saturating_sub(1);
    let matching_glyphs = &font.glyphs[nearest_pixel_size];

    let pixel_size = if font.sdf { requested_pixel_size } else { pixel_size(matching_glyphs) };

    pixelfont::PixelFont { bitmap_font: font, glyphs: matching_glyphs, pixel_size }.into()

View on GitHub (pinned to 3fd8f2ec03)

Solutions

Compile the .slint files with the EmbedForSoftwareRenderer option so fonts are embedded.
Install a fallback font discoverable by the software renderer.

When it happens

Trigger: Thrown at internal/renderers/software/fonts.rs:193 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of slint-ui/slint@3fd8f2ec03 (2026-08-19). Data as JSON: /api/errors/45c4eaee1cb4b28f. Report an issue: GitHub.