Crap Game: Snake but the only instruction is LD

[Seven.FFF]

This is flippin’ genius. Infinite hats doffed to you!

[MrPixel]

I half expected the game code to start screaming at me to let it die. Viewer discretion indeed

[djnzx48]

Are there any other instructions this could be done with other than LD? I was thinking that the shift/rotate instructions look like the best bet, plus you can use the undocumented instructions such as LD B, RLC (IX+d). You could use this along with an address in ROM to effectively load a value into a register, except you'd have to account for the value being shifted over one.

[djnzx48]

Ah no, that wouldn't work because there doesn't seem to be a way to do jumps without somehow modifying the stack pointer, which you can't do with shifts/rotates. Using the all-RAM configuration on a +3 wouldn't really work either because the screen would get in the way.

I did consider either moving the stack to the location of the FRAMES system variable, or setting IY to point to the stack, so that when the interrupt routine increments FRAMES it increments the return address. This would only let you do 256 byte jumps, but if the calling code is after $FF00 it could potentially be used to jump into ROM which then does a RET to the desired location? So maybe a sequel is possible after all

[R-Tape]

Are there any other instructions this could be done with other than LD?

I'm still getting my head around this one! I can see how it loops by repeating LD A,(HL) and changing the stack so the interrupt does it for you, but I need to put a cold flannel on my head and work out how you can do everything else without even using CP!

I wouldn't have thought this possible.

[djnzx48]

Well this technique is very limited

Instead of thinking of branches and choosing whether to do some computation or not based on a condition, you basically always do the computation, but set it up so that if the condition is false you end up with what you had before. So for example, the food always gets drawn every frame, but if there's still food on the screen or if the screen position where it's supposed to appear is occupied, it just draws whatever colour is already on the screen and so nothing changes. There's still a lot of things that are basically impossible to do without resorting to complicated loops, even just adding two numbers or checking whether one value is greater than another.

[MrPixel]

is there a version for the WinAPE?

[MrPixel]

Z80 machine code has a lot of instructions, and it can be difficult trying to keep track of them all. Does PUSH decrement the stack pointer before or afterwards? What's the difference between IFF1 and IFF2? And what exactly does DAA even do?

Well, here's some good news: you don't have to memorise any of these instructions, since it turns out that all of them are in fact useless! (Cries of 'blow me down' and 'well I never'. Ed.) Well, it's true. And to prove it, here's a version of that gaming classic, Snake, where every single instruction is replaced with the humble LD. Nope, there's no trickery or self-modifying code going on here - it's all just LD instructions.

Download here: snake.tap
Runs on any 48K/128K Spectrum. Controls are QAOP or 5678.

Planned features: Extra levels, redefinable keys, multiple speed settings, online leaderboard, ability to make phone calls, VR support, Rolos dispensed when you win...

Source code available here if you want to experience the true horror. Viewer discretion is advised.

please remap the keys to traditional arrow or wasd please

[Seven.FFF]

5678 *is* traditional arrow.

[Kweepa]

Plays like a dream!

[djnzx48]

I was thinking of adding WASD keys but that clashes with QAOP which is more 'traditional', IMHO. I'll probably add redefinable keys in a future update. I don't know anything about Amstrad machines, so no idea if anything like this is possible there.

EDIT: Would ESDF do? It's the same basic configuration but just shifted over one.

[djnzx48]

[mention]MrPixel[/mention] there's a new update here adding ESDF controls in addition to the old QAOP and 5678 controls.

[MrPixel]

I was thinking of adding WASD keys but that clashes with QAOP which is more 'traditional', IMHO. I'll probably add redefinable keys in a future update. I don't know anything about Amstrad machines, so no idea if anything like this is possible there.

EDIT: Would ESDF do? It's the same basic configuration but just shifted over one.

what about I,j,k,l or plain arrow keys. i'm on a latop so the traditional 5,6,7,8 keys are in a straight vertical line, not marked. good game though. i'm amazed that you were able to pull this off. won't run in zxspin assembler though

[MrPixel]

so, the base game is good, impressive even. however, the snake lacks any sort of ability to reverse direction. maybe add in some sort of bumper (like in sonic CD in Collision Chaos) that would help the snake reverse direction. also, some music. take advantage of the Spectrum 128's capabilities and create something suitable. i would also suggest you remove the ground barriers as well as the ceiling as i had some trouble with them. your decision but keep it in mind. happy coding

[djnzx48]

Yeah there are probably too many obstacles, I spent about 5 minutes making the layout for the game so it could definitely be improved. I'd like to add music but there's no way to play it with just the LD instruction, so it would have to be done with some ROM routine and things could get quite tricky. Not sure quite what you mean about reversing direction?

[djnzx48]

New version released here: snake.tap

This release adds variety with new levels every 50 points, adds cursor controls, decreases the game speed and adds a brilliant new loading screen courtesy of [mention]R-Tape[/mention]!

[Ersh]

That's great! Ruddy brilliant screen by R-Tape, love the snake/logo and the background is just clever as hell.

[Joefish]

It's cheating, loading a screen like that. It should load a block of LDs that then draw the screen!