The static representation of a STACK exercise arrives with its images only as PDF files (for example stack-plot-render-0.pdf in the sample article's generated directory). PDF serves the LaTeX/print route well, but an EPUB reading system displays no PDF, and the EPUB specification requires a fallback for any such resource (epubcheck error MED-003).
As of the commit "EPUB: an image available only as PDF leaves a placeholder" (PR #3032), the EPUB conversion does not package a PDF-only image: it issues a build warning and places a text placeholder where the image belongs. So a reader of an EPUB containing STACK exercises currently sees a placeholder instead of a plot.
The durable fix is on the harvesting side: the static representation of each STACK exercise should include both an SVG and a PNG for each image, alongside the PDF. The conversions already choose per output: SVG for EPUB and other web-derived formats, PNG for the Kindle variant (whose images are always PNG). With both present, every route gets its preferred format with no fallback machinery.
cc @geoo89
Claude Fable 5, acting as a coding assistant for Rob Beezer
The static representation of a STACK exercise arrives with its images only as PDF files (for example
stack-plot-render-0.pdfin the sample article's generated directory). PDF serves the LaTeX/print route well, but an EPUB reading system displays no PDF, and the EPUB specification requires a fallback for any such resource (epubcheck error MED-003).As of the commit "EPUB: an image available only as PDF leaves a placeholder" (PR #3032), the EPUB conversion does not package a PDF-only image: it issues a build warning and places a text placeholder where the image belongs. So a reader of an EPUB containing STACK exercises currently sees a placeholder instead of a plot.
The durable fix is on the harvesting side: the static representation of each STACK exercise should include both an SVG and a PNG for each image, alongside the PDF. The conversions already choose per output: SVG for EPUB and other web-derived formats, PNG for the Kindle variant (whose images are always PNG). With both present, every route gets its preferred format with no fallback machinery.
cc @geoo89
Claude Fable 5, acting as a coding assistant for Rob Beezer