If you want to see how this looked like when it first started, go to this Cemetech thread, but from now onwards I'll be crossposting everything from there to here and vice versa.

Anyway! This is an attempt to clone @Deep Thought 's monochrome Fruit Ninja game for the color calcs using xLIBC (as such, it requires Doors CSE to run). The control scheme is pretty similar so far (swipe across the keypad to draw a line onscreen, the screen is mapped from the MATH row downwards, every key works except for ON) except for those annoying dots that appear... but those'll be fixed easily enough.
A demo:


Download here (If you just want the program without the background pic, that's here). The code alone is here.

edit: some more important info from the Cemetech thread--

For those wondering how it works:
You may have noticed that the TI-OS's getKey command maps keys by row, then column. Using the ᴇ, iPart() and fPart() commands, the program extracts those row/column values, multiplies them to make them usable on the screen, and uses the multiplied column value/multiplied row value as X/Y coords to draw the line.

The example in the video uses xLIBC to draw the lines , but I have one that just moves an O around on the homescreen using pure TI-BASIC; that can be found here. (code here)

This is looking pretty sweet so far!
So it's in hybrid basic?

Good luck finishing it off!

Yes it is, and thank you!

I got a decently fast "fruit" (size-3 pixel) working; I don't think the speed at which it travels is quite right, but it's good enough for a test.
Download here.
Dunno if it's gonna be this fast with actual fruit sprites. Fingers crossed for now.

For a vertical line, you just need something like "If (y-y1)*(x2-x1) = (y2-y1)*(x-x1)" or "If (y-y1)*(x2-x1) - (y2-y1)*(x-x1) = 0"
That gets rid of the division by zero. But that also only checks one point. Are you really sure the <17 code works as expected? I would try using the second formula (the one that checks for zero), then check the top left corner of your sprite and the bottom right corner. If one of the equations returns zero, there was a hit. If the signs are different (one positive, one negative) then there was a hit. If the signs are the same, then there was no hit.

I don't really remember TI-BASIC very well, but something like this:
(y-y1)*(x2-x1) - (y2-y1)*(x-x1) -> A
If A = 0
points+1->points
Else
If Sign(A) =/= Sign((y+15-y1)*(x2-x1) - (y2-y1)*(x+15-x1)
points+1->points
EndI don't think there's really a Sign function, but something along those lines should work ok...

Ah, that's a neat trick. But thinking about it later, i'm pretty sure what i posted above won't work either. It might work for infinite lines, but you'd have to check both sets of opposite corners.

good to know you got it fixed!