Overview

MicroW8 loads WebAssembly modules with a maximum size of 256kb. You module needs to export a function fn upd() which will be called once per frame. After calling upd MicroW8 will display the 320x240 8bpp framebuffer located at offset 120 in memory with the 32bpp palette located at 0x13000.

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

Memory map

00000-00040: user memory
00040-00044: time since module start in ms
00044-0004c: gamepad state
0004c-00078: reserved
00078-12c78: frame buffer
12c78-13000: reserved
13000-13400: palette
13400-13c00: font
13c00-14000: reserved
14000-40000: user memory

API

All API functions are found in the env module.

Math

These all do what you'd expect them to. All angles are in radians.

fn asin(x: f32) -> f32

Returns the arcsine of x.

fn acos(x: f32) -> f32

Returns the arccosine of x.

fn atan(f32) -> f32

Returns the arctangent of x.

fn atan2(y: f32, y: f32) -> f32

Returns the angle between the point (x, y) and the positive x-axis.

fn sin(angle: f32) -> f32

Returns the sine of angle.

fn tan(angle: f32) -> f32

Returns the tangent of angle.

fn cos(angle: f32) -> f32

Returns the cosine of angle.

fn exp(x: f32) -> f32

Returns e^x.

fn log(x: f32) -> f32

Returns the natural logarithmus of x. Ie. e^log(x) == x.

fn pow(x: f32, y: f32) -> f32

Returns x^y.

fn fmod(x: f32, y: f32) -> f32

Returns x modulo y, ie. x - floor(x / y) * y. This means the sign of the result of fmod is the same as y.

Random

MicroW8 provides a pretty good PRNG, namely xorshift64*. It is initialized to a constant seed at each startup, so if you want to vary the random sequence you'll need to provide a seed yourself.

fn random() -> i32

Returns a (pseudo-)random 32bit integer.

fn randomf() -> f32

Returns a (pseudo-)random float equally distributed in [0,1).

fn randomSeed(seed: i32)

Seeds the PRNG with the given seed. The seed function is reasonably strong so that you can use

randomSeed(index);
random()

as a cheap random-access PRNG (aka noise function).

Graphics

The default palette can be seen here. (Press Z on the keyboard to switch to palette.)

The palette can be changed by writing 32bit rgba colors to addresses 0x13000-0x13400.

The drawing functions are sub-pixel accurate where applicable (line, circle). Pixel centers lie halfway between integer coordinates. Ie. the top-left pixel covers the area 0,0 - 1,1, with 0.5,0.5 being the pixel center.

fn cls(color: i32)

Clears the screen to the given color index. Also sets the text cursor to 0, 0 and disables graphical text mode.

fn setPixel(x: i32, y: i32, color: i32)

Sets the pixel at x, y to the given color index.

fn getPixel(x: i32, y: i32) -> i32

Returns the color index at x, y. Returns 0 if the given coordinates are outside the screen.

fn hline(left: i32, right: i32, y: i32, color: i32)

Fills the horizontal line [left, right), y with the given color index.

fn rectangle(x: f32, y: f32, w: f32, h: f32, color: i32)

Fills the rectangle x,y - x+w,y+h with the given color index.

(Sets all pixels where the pixel center lies inside the rectangle.)

fn circle(cx: f32, cy: f32, radius: f32, color: i32)

Fills the circle at cx, cy and with radius with the given color index.

(Sets all pixels where the pixel center lies inside the circle.)

fn rectangle_outline(x: f32, y: f32, w: f32, h: f32, color: i32)

Draws a one pixel outline on the inside of the given rectangle.

(Draws the outermost pixels that are still inside the rectangle area.)

fn circle_outline(cx: f32, cy: f32, radius: f32, color: i32)

Draws a one pixel outline on the inside of the given circle.

(Draws the outermost pixels that are still inside the circle area.)

fn line(x1: f32, y1: f32, x2: f32, y2: f32, color: i32)

Draws a line from x1,y1 to x2,y2 in the given color index.

Input

MicroW8 provides input from a gamepad with one D-Pad and 4 buttons, or a keyboard emulation thereof.

The buttons are numbered

In addition to using the API functions below, the gamepad state can also be read as a bitfield of pressed buttons at address 0x44. 0x48 holds the buttons that were pressed last frame.

fn isButtonPressed(btn: i32) -> i32

Returns whether the buttons with the given index is pressed this frame.

fn isButtonTriggered(btn: i32) -> i32

Returns whether the given button is newly pressed this frame.

fn time() -> f32

Returns the time in seconds since the start of the cart.

The integer time in milliseconds can also be read at address 0x40.

Text output

The default font can be seen here.

The font can be changed by writing 1bpp 8x8 characters to addresses 0x13400-0x13c00.

All text printing is done at the cursor position, which is advanced after printing each character. The cursor is not visible.

Text printing can operate in two modes - normal and graphics. After startup and after cls() normal mode is active.

Normal mode

In normal mode, text printing is constrained to an 8x8 character grid. Setting the cursor position to 2,3 will start printing at pixel coordinates 16,24.

When printing characters, the full 8x8 pixels are painted with the text and background colors according to the character graphics in the font.

When moving/printing past the left or right border the cursor will automatically wrap to the previous/next line. When moving/printing past the upper/lower border, the screen will be scrolled down/up 8 pixels, filling the fresh line with the background color.

Graphics mode

In graphics mode, text can be printed to any pixel position, the cursor position is set in pixel coordinates.

When printing characters only the foreground pixels are set, the background is "transparent".

Moving/printing past any border does not cause any special operation, the cursor just goes off-screen.

Control chars

Characters 0-31 are control characters and don't print by default. They take the next 0-2 following characters as parameters. Avoid the reserved control chars, they are currently NOPs but their behavior can change in later MicroW8 versions.

(*) In graphics mode, the x coordinate is doubled when using control char 31 to be able to cover the whole screen with one byte.

fn printChar(char: i32)

Prints the character in the lower 8 bits of char. If the upper 24 bits are non-zero, right-shifts char by 8 bits and loops back to the beginning.

fn printString(ptr: i32)

Prints the zero-terminated string at the given memory address.

fn printInt(num: i32)

Prints num as a signed decimal number.

fn setTextColor(color: i32)

Sets the text color.

fn setBackgroundColor(color: i32)

Sets the background color.

fn setCursorPosition(x: i32, y: i32)

Sets the cursor position. In normal mode x and y are multiplied by 8 to get the pixel position, in graphics mode they are used as is.

The uw8 tool

The uw8 tool included in the MicroW8 download includes a number of useful tools for developing MicroW8 carts. For small productions written in wat or CurlyWas you don't need anything apart from uw8 and a text editor of your choice.

uw8 run

Usage:

uw8 run [<options>] <file>

Runs <file> which can be a binary WebAssembly module, an .uw8 cart, a wat (WebAssembly text format) source file or a CurlyWas source file.

Options:

• -w, --watch: Reloads the given file every time it changes on disk.
• -p, --pack: Pack the file into an .uw8 cart before running it and print the resulting size.
• -u, --uncompressed: Use the uncompressed uw8 format for packing.
• -l LEVEL, --level LEVEL: Compression level (0-9). Higher compression levels are really slow.
• -o FILE, --output FILE: Write the loaded and optionally packed cart back to disk.

uw8 pack

Usage:

uw8 pack [<options>] <infile> <outfile>

Packs the WebAssembly module or text file, or CurlyWas source file into a .uw8 cart.

Options:

• -u, --uncompressed: Use the uncompressed uw8 format for packing.
• -l LEVEL, --level LEVEL: Compression level (0-9). Higher compression levels are really slow.

uw8 filter-exports

Usage:

uw8 filter-exports <infile> <outfile>

Reads a binary WebAssembly module, removes all exports not used by the MicroW8 platform + everything that is unreachable without those exports and writes the resulting module to outfile.

When compiling C code (or Rust, zig or others) to WebAssembly, you end up with a few exported global variables that are used for managing the heap and C stack, even if the code doesn't actually use those features. You can use this command to automatically remove those and gain a few bytes. See the C, Rust and zig examples in the MicroW8 repository.

Distribution

Base64 encoded link

url parameter

.html + .uw8

Itch.io

.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 () -> void and an export section that exports the first function in the file under the name upd.

Format version 02:

Same as version 01 except everything after the first byte is compressed using a custom LZ compression scheme.