0-Row Sprites

[12Me21]

I was using DXY0 as a simple method to create a single frame of delay, but Octo assumes this is the Super Chip instruction, which draws a 16 pixel sprite instead.

[JohnEarnest]

After extensive consideration, I've decided to avoid creating a new feature flag for this. Drawing a 1-pixel tall blank sprite with the vblank flag enabled will achieve your desired effect provided you can find a zero byte anywhere in your program, which should be trivial to arrange.

[tobiasvl]

@JohnEarnest Note that this behavior is (as far as I can gather) unique to Octo, which means that games written with Octo as a target platform that use DXY0 to draw a 16x16 sprite in low-resolution mode will not work in anything but Octo. (Your own "Eaty the Alien" comes to mind.)

Considering the number of games out there that use DXY0 as a delay routine is probably zero (at least now that 12Me21 has been dissuaded from doing it), that in itself might not be a reason to add a feature/quirks flag to Octo, but in fact the CHIP-8 interpreter for the DREAM 6800 computer used DXY0 to draw an 8x16 sprite.

So there are three different low-resolution behaviors of DXY0 that I know of: 8x16 sprite drawing (DREAM 6800), 16x16 sprite drawing (Octo) and no-op with a "vblank delay" (most/all other implementations),

[JohnEarnest]

@tobiasvl the compromise I came up with was to make it so that the linter warns of using 16x16 sprites in low-res mode:

https://github.com/JohnEarnest/Octo/blob/gh-pages/js/debugger.js#L210-L212

Thus, authors are assisted in writing portable programs if they wish to do so.