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 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

fn printChar(char: i32)

fn printString(ptr: i32)

fn printInt(num: i32)

fn setTextColor(color: i32)

fn setBackgroundColor(color: i32)

fn setCursorPosition(x: i32, y: i32)

.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.