Palette does not work as expected

[ttulka]

Consider this AS code:

import * as w4 from "./wasm4";

store<u32>(w4.PALETTE, 0xe0f8cf, 0);    // light
store<u32>(w4.PALETTE, 0xe30000, 1);    // red
store<u32>(w4.PALETTE, 0x306850, 2);    // green
store<u32>(w4.PALETTE, 0x000000, 3);    // black

export function update (): void {
  // nothing here
}

I would expect the background colored in light green, but some kind of violet appears:

Works fine when the other three colors are not set.

[aduros]

Hmm, it turns out the 3rd param to store is in bytes and not in elements. So it should be:

store<u32>(w4.PALETTE, 0xff0000, 0);    // light
store<u32>(w4.PALETTE, 0xe30000, 4);    // red
store<u32>(w4.PALETTE, 0x306850, 8);    // green
store<u32>(w4.PALETTE, 0x000000, 12);    // black

I'll update the docs accordingly.

[ttulka]

Yeah, it is not very use-friendly... What about making it explicit that only four colors are supported?:

store<u32>(w4.PALETTE_1, 0xff0000);    // light
store<u32>(w4.PALETTE_2, 0xe30000);    // red
store<u32>(w4.PALETTE_3, 0x306850);    // green
store<u32>(w4.PALETTE_4, 0x000000);    // black

Some more high-level API wouldn't be quite bad, too:

w4.setPallete(0xff0000, 1);
w4.setPallete(0xe30000, 2);
w4.setPallete(0x306850, 3);
w4.setPallete(0x000000, 4);

Or even?:

w4.setPallete1(0xff0000);
w4.setPallete2(0xe30000);
w4.setPallete3(0x306850);
w4.setPallete4(0x000000);

// or...

w4.setPallete(0xff0000, 0xe30000, 0x306850, 0x000000);

[aduros]

PALETTE1 to PALETTE4 sounds good!

I think we should also ask the AssemblyScript folks if there's a bug with the 3rd param to store. This documentation seems wrong https://www.assemblyscript.org/introduction.html#low-level-perspective

[ttulka]

documentation seems wrong

Could you collaborate more?

The AS community is very active on Discord, that would be the best plate where to ask.

[aduros]

Could you collaborate more?

In the store() example at that link, the 3rd param should be 32 instead of 8 to match the C example... I'll ping Discord about it.

[aduros]

Opened https://github.com/AssemblyScript/assemblyscript/issues/2044

[ttulka]

Cool!

[aduros]

So unfortunately the AS behavior is intended and the documentation was just wrong. I changed the WASM-4 documentation to use sizeof() to calculate the array index positions. Let's let that sit for a bit and see how it feels before adding PALETTE1-4.

[ttulka]

In Snake, I have already used

store<u32>(w4.PALETTE, 0xe0f8cf, 0 * sizeof<u32>());

But I find it plain ugly. Especially in JS-related languages such as AS, things like sizeof are very alien.

Another benefit of using PALETTE1-4 would be preventing developers from writing:

store<u32>(w4.PALETTE, 0xe0f8cf, 5 * sizeof<u32>());

It is really not a big deal, but IMHO it would increase the Developer Experience.

What speaks against that?

[eXponenta]

There are a lot of another ways to damage WASM memory.
You can wrap pallete inside your app on AS like this (you can remove trash code, this is generic pointer):

https://github.com/AssemblyScript/assemblyscript/blob/main/tests/compiler/std/pointer.ts

[MaxGraey]

It should be

store<u32>(w4.PALETTE, 0xe0f8cf, 0 * sizeof<u32>());    // light
store<u32>(w4.PALETTE, 0xe30000, 1 * sizeof<u32>());    // red
store<u32>(w4.PALETTE, 0x306850, 2 * sizeof<u32>());    // green
store<u32>(w4.PALETTE, 0x000000, 3 * sizeof<u32>());    // black