microw8/site/content/_index.md

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Versions

• v0.1pre1

Spec

MicroW8 loads WebAssembly modules with a maximum size of 256kb. You module needs to export a function fn tic(time: i32) which will be called once per frame. After calling tic MicroW8 will display the 320x256 8bpp framebuffer located at offset 120 in memory.

The memory has to be imported as "env" "memory" and has a maximum size of 256kb (4 pages).

Other imports provided by the platform:

• in module math:
• • fn acos(f32) -> f32
• • fn asin(f32) -> f32
• • fn atan(f32) -> f32
• • fn atan2(f32, f32) -> f32
• • fn cos(f32) -> f32
• • fn exp(f32, f32) -> f32
• • fn log(f32) -> f32
• • fn sin(f32) -> f32
• • fn tan(f32) -> f32
• • fn pow(f32) -> f32

.uw8 format

The first byte of the file specifies the format version:

Format version 00:

This file is simply a standard WebAssembly module

Format version 01:

The rest of this file is the same as a WebAssembly module with the 8 byte header removed. This module can leave out sections which are then taken from a base module provided by MicroW8.

You can generate this base module yourself using uw8-tool. As a quick summary, it provides all function types with up to 5 parameters (i32 or f32) where the f32 parameters always preceed the i32 parameters. Then it includes all imports that MicroW8 provides, a function section with a single function of type (i32) -> void and an export section that exports the first function in the file under the name tic.

Tooling

The Web Assembly Binary Toolkit includes a few useful tools, eg. wat2wasm to compile the WebAssemby text format to binary wasm and wasm2wat to disassemble wasm binaries.

If you don't like the look of the .wat text format, you might want to take a look at CurlyWas, a curly-braces infix syntax for WebAssembly.

Once you have a size-efficient .wasm file, you can use uw8-tool (currently included in the MicroW8 repository) to strip off sections of the WebAssembly module that are provided by the MicroW8 platform.

Writing code for MicroW8 in C, Rust, AssemblyScript etc. should absolutely possible but no examples are provided, yet.

Examples

• Technotunnel (199 bytes): A port of my entry in the Outline'21 bytebattle quater final
• XorScroll (50 bytes): A simple scrolling XOR pattern. Fun fact: This is the pre-loaded effect when entering a bytebattle.