I realized that the PDF engines of modern desktop browsers (PDFium and PDF.js) support JavaScript with enough I/O primitives to make a basic game like Tetris.<p>It was a bit tricky to find a union of features that work in both engines, but in the end it turns out that showing/hiding annotation "fields" works well to make monochrome pixels, and keyboard input can be achieved by typing in a text input box.<p>All in all it's quite janky but a nice reminder of how general purpose PDF scripting can be. The linked PDF is all ASCII so you can just open it in a text editor, or have a look at the source code here: <a href="https://github.com/ThomasRinsma/pdftris/blob/main/gengrid.py">https://github.com/ThomasRinsma/pdftris/blob/main/gengrid.py</a>