If the resolution you're sending into the projector matches the native/optimal/recommended resolution of the projector (in at least the long dimension, and it will letterbox the other dimension), and you set the digital keystone to neutral/zero, you will achieve a 1:1 pixel mapping that is required to be in compliance with the author's statement that "These examples will only work if your [browser|projector|etc]* doesn’t do any rescaling on the images below."
* Author only said browser, but actually everything in the chain matters. If you're not at a 1:1 pixel mapping you're resampling, and resampling breaks the checkerboard example. Digital keystone (but not optical keystone with tilting lenses) included.
* Author only said browser, but actually everything in the chain matters. If you're not at a 1:1 pixel mapping you're resampling, and resampling breaks the checkerboard example. Digital keystone (but not optical keystone with tilting lenses) included.