WebAssembly Simulator for Rust on Mynewt with LVGL

Note: This is the mynewt branch that supports Watch Faces built with Rust on Mynewt

Simulate Rust on Mynewt Watch Face in Web Browser (with WebAssembly), for easier development of custom watch faces

Online Simulator Demo
Watch Face Source Code
Watch Face Crate on crates.io
GitHub Actions Workflow for Simulator

Features

Compiles actual Rust On Mynewt Watch Face from Rust to WebAssembly without any code changes
Uses GitHub Actions Workflow to build any Rust Watch Face into WebAssembly. Browse Rust Watch Faces
Renders LVGL to HTML Canvas directly via WebAssembly, without using SDL2. See lvgl.html
Supports RGB565 Framebuffer Format used by PineTime Display Controller, so that bitmaps will be rendered correctly
Shows current Date and Time
Supports multiple Fonts and Bitmaps

Upcoming Features

Accept Touch Input for LVGL
Allow Watch Faces to be built online in Rust with online preview

References

"Create Your Own PineTime Watch Face in Rust... And Publish on crates.io"
"Preview PineTime Watch Faces in your Web Browser with WebAssembly"

How To Build The Simulator

To build PineTime Watch Face Simulator on Linux, macOS or Windows (without WSL), follow these steps based on the GitHub Actions Workflow .github/workflows/simulator.yml...

Install emscripten (emsdk) and wabt. See instructions below.
Install Rust from rustup.rs
Enter...
```
git clone --branch mynewt  https://github.com/AppKaki/lvgl-wasm
cd lvgl-wasm
```
The emsdk and lvgl-wasm folders should be installed at the same folder level.

Build the Rust app...

rustup default nightly
rustup target add wasm32-unknown-emscripten
cargo build

Ignore this error, we'll fix in the next step...

error[E0432]: unresolved import `ad`
--> /home/runner/.cargo/registry/src/github.com-1ecc6299db9ec823/cty-0.1.5/src/lib.rs:8:9
pub use ad::*;
^^ maybe a missing crate `ad`?

Change $HOME/.cargo/registry/src/github.com-*/cty-0.1.5/src/lib.rs

From...

target_arch = "arm"

To...

target_arch = "arm", target_arch = "wasm32"

Here is the sed script that makes the change...

cat $HOME/.cargo/registry/src/github.com-*/cty-0.1.5/src/lib.rs \
    | sed 's/target_arch = "arm"/target_arch = "arm", target_arch = "wasm32"/' \
    >/tmp/lib.rs
cp /tmp/lib.rs $HOME/.cargo/registry/src/github.com-*/cty-0.1.5/src/lib.rs
rm /tmp/lib.rs

(Optional) Inject the Watch Face Crate into lvgl-wasm.

By default lvgl-wasm builds the WebAssembly Simulator with the Barebones Watch Face. Skip this step to use the default Watch Face.

Assuming that my_watchface::MyWatchFace is the Watch Face that will be built into the Simulator...

Change mynewt/wasm/Cargo.toml from

barebones-watchface = "x.x.x"

to

# If my-watchface is on crates.io...
my-watchface = "x.x.x"

# If my-watchface is on GitHub...
my-watchface = { git = "https://github.com/..." }

Change mynewt/wasm/src/lib.rs from

use barebones_watchface::watchface::lvgl::mynewt::fill_zero;
use barebones_watchface::watchface::{self, WatchFace};
type WatchFaceType = barebones_watchface::BarebonesWatchFace;

to

use my_watchface::watchface::lvgl::mynewt::fill_zero;
use my_watchface::watchface::{self, WatchFace};
type WatchFaceType = my_watchface::MyWatchFace;

For the sed script, see barebones-watchface/.github/workflows/simulator.yml

Build the LVGL WebAssembly app containing our Watch Face...
```
cargo build
source emsdk/emsdk_env.sh
make -f mynewt/Makefile
```
For Windows (without WSL): See the build instructions in mynewt/build.cmd

If we see this error...

emscripten:ERROR: emscript: failure to parse metadata output from wasm-emscripten-finalize

Revert to the older working version of emscripten...

emsdk/emsdk install 2.0.6
make -f mynewt/Makefile

Copy the generated WebAssembly files to the docs folder (used by GitHub Pages)...
```
cp wasm/lvgl.js wasm/lvgl.wasm docs
```
For Windows (without WSL):
```
copy wasm/lvgl.js wasm/lvgl.wasm docs
```
We don't need lvgl.html because docs already contains a version of lvgl.html with custom JavaScript.
Start a Web Server for the docs folder, because WebAssembly doesn't work when opened from the filesystem.

For Linux: Use darkhttpd...
```
darkhttpd docs
```
For macOS and Windows: Use the Chrome Extension Web Server for Chrome and set the folder to docs
Launch a Web Browser and open the URL shown by darkhttpd or Web Server for Chrome.

Enter lvgl.html in the URL bar to view the PineTime Watch Face Simulator.

In case of problems, compare with the following...

GitHub Actions workflow
GitHub Actions build log (look for mynewt branch)

Install emscripten on Windows Without WSL

To install emscripten on plain old Windows without WSL...

# Get the emsdk repo
git clone https://github.com/emscripten-core/emsdk.git

# Enter that directory
cd emsdk

# Download and install version 2.0.6 of the SDK tools. The latest version 2.0.7 fails to build lvgl-wasm.
emsdk.bat install 2.0.6
        
# Make version 2.0.6 active for the current user (writes .emscripten file)
emsdk.bat activate 2.0.6

# Activate PATH and other environment variables in the current terminal
emsdk_env.bat

# Show version
emcc --version
emcc --version

Install emscripten on macOS

Enter these commands according to the docs...

# Get the emsdk repo
git clone https://github.com/emscripten-core/emsdk.git

# Enter that directory
cd emsdk

# Download and install version 2.0.6 of the SDK tools. The latest version 2.0.7 fails to build lvgl-wasm.
./emsdk install 2.0.6
        
# Make version 2.0.6 active for the current user (writes .emscripten file)
./emsdk activate 2.0.6

# Activate PATH and other environment variables in the current terminal
source ./emsdk_env.sh

# Show version
emcc --version
emcc --version

If we see this error...

+ exec python ./emsdk.py install latest
Installing SDK 'sdk-releases-upstream-d7a29d82b320e471203b69d43aaf03b560eedc54-64bit'..
Installing tool 'node-12.18.1-64bit'..
Error: Downloading URL 'https://storage.googleapis.com/webassembly/emscripten-releases-builds/deps/node-v12.18.1-darwin-x64.tar.gz': <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed (_ssl.c:777)>
Warning: Possibly SSL/TLS issue. Update or install Python SSL root certificates (2048-bit or greater) supplied in Python folder or https://pypi.org/project/certifi/ and try again.
Installation failed!

Try installing the latest Python 3 via brew install. Then edit the shell script emsdk/emsdk and set EMSDK_PYTHON to the path of the installed Python 3 executable...

# Insert this line before exec
EMSDK_PYTHON=/usr/local/Cellar/python@3.8/3.8.5/bin/python3

exec "$EMSDK_PYTHON" "$0.py" "$@"

Install emscripten on Ubuntu x64 and Windows WSL

(If you're using plain old Windows without WSL, check the instructions above under "Install emscripten on Windows Without WSL")

To install emscripten on Ubuntu x64 and Windows WSL...

# Get the emsdk repo
git clone https://github.com/emscripten-core/emsdk.git

# Enter that directory
cd emsdk

# Download and install version 2.0.6 of the SDK tools. The latest version 2.0.7 fails to build lvgl-wasm.
./emsdk install 2.0.6
        
# Make version 2.0.6 active for the current user (writes .emscripten file)
./emsdk activate 2.0.6

# Activate PATH and other environment variables in the current terminal
source ./emsdk_env.sh

# Show version
emcc --version
emcc --version

Alternatively, use the prebuilt emscripten binary for Ubuntu x64...

# Download the emscripten binary from lvgl-wasm
curl -L https://github.com/AppKaki/lvgl-wasm/releases/download/v1.0.0/emsdk.tgz -o emsdk.tgz

# Unzip to emsdk
tar xzf emsdk.tgz
rm emsdk.tgz

# Activate PATH and other environment variables in the current terminal
source emsdk/emsdk_env.sh

# Show version
emcc --version
emcc --version

This is based on the GitHub Actions Workflow: .github/workflows/simulator.yml...

Look for the steps "Install emscripten" and "Install wabt"
Change /tmp to a permanent path like ~

Then add emscripten and wabt to the PATH...

# Add emscripten and wabt to the PATH
source ~/emsdk/emsdk_env.sh
export PATH=$PATH:~/wabt/build

Install emscripten on Arch Linux / Manjaro Arm64

Works on Pinebook Pro with Manjaro...

sudo pacman -S emscripten
sudo pacman -S wabt
source /etc/profile.d/emscripten.sh
emcc --version
# Shows emscripten version 1.39.20
wasm-as --version
# Shows binaryen version 95

For emscripten version 1.40.x and newer

emscripten and binaryen will probably work, skip the rest of this section.

For emscripten version 1.39.x and binaryen version 95 only

This will fail during the build, because emscripten 1.39 needs binaryen version 93, not 95.

We could install binaryen version 93... But emcc will fail with an error "stackSave already exists". That's because binaryen 93 generates the "stackSave" that conflicts with emscripten 1.39.20. More details here

To fix this, we install binaryen version 94, but rename it as version 93...

# Download binaryen 94
git clone --branch version_94 https://github.com/WebAssembly/binaryen
cd binaryen
nano CMakeLists.txt

Change

   project(binaryen LANGUAGES C CXX VERSION 94)

To

   project(binaryen LANGUAGES C CXX VERSION 93)

Then build and install binaryen...

cmake .
make -j 5
sudo cp bin/* /usr/bin
sudo cp lib/* /usr/lib
wasm-as --version
# Shows binaryen "version 93 (version_94)"

binaryen is now version 93, which is correct. Proceed to build the app...

cd lvgl-wasm
rm -rf ~/.emscripten_cache
make clean
make -j 5

The app build should complete successfully.

emcc Error: Unexpected binaryen version

If we see this error...

   emcc: error: unexpected binaryen version: 95 (expected 93) [-Wversion-check] [-Werror]
   FAIL: Compilation failed!: ['/usr/lib/emscripten/emcc', '-D_GNU_SOURCE', '-o', '/tmp/tmpbe4ik5na.js', '/tmp/tmpzu5jusdg.c', '-O0', '--js-opts', '0', '--memory-init-file', '0', '-Werror', '-Wno-format', '-s', 'BOOTSTRAPPING_STRUCT_INFO=1', '-s', 'WARN_ON_UNDEFINED_SYMBOLS=0', '-s', 'STRICT=1', '-s', 'SINGLE_FILE=1']

Then we need to install the right version of binaryen (see above)

emcc Error: stackSave already exists

If we see this error...

   Fatal: Module::addExport: stackSave already exists
   emcc: error: '/usr/bin/wasm-emscripten-finalize --detect-features --global-base=1024 --check-stack-overflow /tmp/emscripten_temp_84xtyzya/tmpzet09r88.wasm -o /tmp/emscripten_temp_84xtyzya/tmpzet09r88.wasm.o.wasm' failed (1)
   FAIL: Compilation failed!: ['/usr/lib/emscripten/emcc', '-D_GNU_SOURCE', '-o', '/tmp/tmpzet09r88.js', '/tmp/tmpxk8zxvza.c', '-O0', '--js-opts', '0', '--memory-init-file', '0', '-Werror', '-Wno-format', '-s', 'BOOTSTRAPPING_STRUCT_INFO=1', '-s', 'WARN_ON_UNDEFINED_SYMBOLS=0', '-s', 'STRICT=1', '-s', 'SINGLE_FILE=1']

That means binaryen 93 generates the "stackSave" that conflicts with emscripten 1.39.20. More details here

We need to install branch version_94 of binaryen, change version in CMakeLists.txt to version 93 (see above)

How It Works

The WebAssembly Simulator is compiled as multiple parts...

Watch Face Library in Rust, from mynewt/wasm

Compiled with cargo with target wasm32-unknown-emscripten into a WebAssembly Static Library: target/wasm32-unknown-emscripten/debug/libwasm.a

Contains the selected Watch Face code and WebAssembly interface mynewt/wasm
LVGL Library in C, from src

Compiled from C to WebAssembly with emscripten
WebAssembly Interface in C, from wasm/lvgl.c

Compiled from C to WebAssembly with emscripten

The Makefile mynewt/Makefile links the above into WebAssembly like this...

emcc -o wasm/lvgl.html \
	-Wl,--start-group \
  target/wasm32-unknown-emscripten/debug/libwasm.a \
	(List of C and C++ object files from LVGL and Sandbox) \
	-Wl,--end-group \
	-g \
	-I src/lv_core \
	-D LV_USE_DEMO_WIDGETS \
	-s WASM=1 \
    -s "EXPORTED_FUNCTIONS=[ '_main', '_get_display_buffer', '_get_display_width', '_get_display_height', '_test_display', '_init_display', '_render_display', '_render_widgets', '_create_clock', '_refresh_clock', '_update_clock' ]"

The emscripten compiler emcc generates three files in folder wasm...

lvgl.wasm: WebAssembly Executable Code, containing our Watch Face, LVGL and the Sandbox. Sample File
lvgl.js: Provides the JavaScript glue that's needed to load lvgl.wasm and run it in a Web Browser. Sample File
lvgl.html: The HTML file that calls lvgl.js to render the user interface.

We won't be using this file, because we have a custom version of lvgl.html

EXPORTED_FUNCTIONS are the C functions that will be exposed from WebAssembly to JavaScript. See the section on "Exported Functions" below.

Rename the HTML files

Because we use a custom lvgl.html, we rename the generated lvgl.html to prevent overwriting...

# Rename the HTML files so we don't overwrite the updates
mv wasm/lvgl.html wasm/lvgl.old.html

Dump the WebAssembly modules

For troubleshooting, we may dump the text version of the WebAssembly module to lvgl.txt...

# Dump the WebAssembly modules
wasm-objdump -x wasm/lvgl.wasm >wasm/lvgl.txt

Sample lvgl.txt

Patch for `cty` crate

This error appears because WebAssembly is not defined for the imported C types...

error[E0432]: unresolved import `ad`
 --> /home/luppy/.cargo/registry/src/github.com-1ecc6299db9ec823/cty-0.1.5/src/lib.rs:8:9
  |
8 | pub use ad::*;
  |         ^^ maybe a missing crate `ad`?

Edit ~/.cargo/registry/src/github.com-*/cty-0.1.5/src/lib.rs

Under aarch64, insert a line for wasm32...

#[cfg(any(target_arch = "aarch64",
          target_arch = "arm",
          target_arch = "asmjs",
          target_arch = "powerpc",
          target_arch = "powerpc64",
          target_arch = "s390x",
          target_arch = "wasm32"))]
mod ad {
    pub type c_char = ::c_uchar;

    pub type c_int = i32;
    pub type c_uint = u32;
}

If we see this error...

error: language item required, but not found: `eh_personality`

Check Cargo.toml...

[profile.dev]
panic         = "abort"     # Disable stack unwinding on panic

Rust on Mynewt Sandbox

Our WebAssembly Simulator runs in a Web Browser based on WebAssembly (somewhat similar to Java Applets). More about WebAssembly

Our Watch Face Crate calls functions from two providers...

LVGL Library (Version 7) for UI widgets
PineTime Watch Face Framework for current date / time, Bluetooth status and power status

lvgl-wasm simulates the minimal set of functions needed for rendering Watch Faces.

Hence lvgl-wasm works like a Sandbox. Here's how the Sandbox works...

Exported Functions

The Sandbox exports the following WebAssembly functions from Rust to JavaScript...

Clock Functions

These functions create the Watch Face, render the LVGL widgets on the Watch Face, and update the time...

create_clock()

Create the Watch Face. Calls pinetime-watchface to create an instance of the Watch Face from the Watch Face Crate.

From mynewt/wasm/src/lib.rs
refresh_clock()

Redraw the Watch Face. Currently does nothing.

From mynewt/wasm/src/lib.rs
update_clock(year, month, day, hour, minute, second)

Set the current date and time. Calls pinetime-watchface to redraw the instance of the Watch Face from the Watch Face Crate.

From mynewt/wasm/src/lib.rs

TODO: This code needs to be fixed to show the correct day of week

Display Functions

These functions initialise the LVGL library and render the LVGL Widgets to the WebAssembly Display Buffer...

init_display()

Init the LVGL display.

From wasm/lvgl.c
render_display()

Render the LVGL display in 16-bit RGB565 format. From wasm/lvgl.c

Calls the WebAssembly Display Driver defined in wasm/lv_port_disp.c

Which calls put_display_px() to draw individual pixels to the the WebAssembly Display Buffer: wasm/lvgl.c

Display Buffer Functions

The WebAssembly Display Driver maintains a Display Buffer: 240 x 240 array of pixels, 4 bytes per pixel, in RGBA colour format: wasm/lvgl.c

///  RGBA WebAssembly Display Buffer that will be rendered to HTML Canvas
#define LV_HOR_RES_MAX          240
#define LV_VER_RES_MAX          240
#define DISPLAY_BYTES_PER_PIXEL 4
uint8_t display_buffer[LV_HOR_RES_MAX * LV_VER_RES_MAX * DISPLAY_BYTES_PER_PIXEL];

Our JavaScript code copies the Display Buffer from WebAssembly Memory and renders to HTML Canvas by calling the following functions...

get_display_width()

Returns 240, the width of the WebAssembly Display Buffer.

From wasm/lvgl.c
get_display_height()

Returns 240, the height of the WebAssembly Display Buffer.

From wasm/lvgl.c
get_display_buffer()

Return the WebAssembly Address of the WebAssembly Display Buffer.

From wasm/lvgl.c

Note that JavaScript is allowed to read and write to WebAssembly Memory (treating it like a JavaScript array of bytes). But WebAssembly can't access any JavaScript Memory.

That's why we designed the Display Buffer Functions to manipulate WebAssembly Memory.

Test Functions

For testing only...

test_display()

(For Testing) Render a colour box to the WebAssembly Display Buffer.

From wasm/lvgl.c
render_widgets()

(For Testing) Render a Button Widget and a Label Widget.

From wasm/lvgl.c

Other Functions

main(): Does nothing.

From wasm/lvgl.c

Simulator JavaScript

The JavaScript functions here call the Exported WebAssembly Functions to render the Watch Face. From docs/lvgl.html

Initialise WebAssembly

We register a callback in the emscripten API, to be notified when the WebAssembly Module lvgl.wasm has been loaded...

//  In JavaScript: Wait for emscripten to be initialised
Module.onRuntimeInitialized = function() {
  //  Render LVGL to HTML Canvas
  render_canvas();
};

Initialise LVGL Display

When the WebAssembly Module lvgl.wasm has been loaded, we call the WebAssembly Function init_display() to initialise the LVGL display...

/// In JavaScript: Create the Watch Face in WebAssembly
function render_canvas() {
  //  Init LVGL Display
  Module._init_display();

Create Watch Face

Then we create the LVGL Watch Face Class from Clock.cpp...

  //  Create the Watch Face in WebAssembly
  Module._create_clock();

Update Watch Face Time

Every minute we update the Watch Face time in DateTimeController...

/// In JavaScript: Update the Watch Face time in WebAssembly and render the WebAssembly Display Buffer to the HTML Canvas
function updateCanvas() {
  //  Update the WebAssembly Date and Time: year, month, day, hour, minute, second
  const localTime = new Date();
  const timezoneOffset = localTime.getTimezoneOffset();  //  In mins
  //  Compensate for the time zone
  const now = new Date(
    localTime.valueOf()             //  Convert time to millisec
    - (timezoneOffset * 60 * 1000)  //  Convert mins to millisec
  );
  Module._update_clock(
    now.getFullYear(),
    now.getMonth() - 1,  //  getMonth() returns 1 to 12
    now.getDay(), 
    now.getHours(),
    now.getMinutes(),
    now.getSeconds()
  );

Note that we need to compensate for the timezone.

Redraw Watch Face

And redraw the Watch Face in Clock.cpp...

  //  Update the Watch Face time in WebAssembly
  Module._refresh_clock();

Render LVGL Widgets to WebAssembly Display Buffer

We call LVGL to render the Widgets into the WebAssembly Display Buffer...

  //  Render LVGL Widgets to the WebAssembly Display Buffer
  Module._render_display();

Resize HTML Canvas

We resize the HTML Canvas to PineTime's 240 x 240 resolution, scaled by 2 times...

  const DISPLAY_SCALE = 2;  //  Scale the canvas width and height

  //  Fetch the PineTime dimensions from WebAssembly Display Buffer
  var width = Module._get_display_width();
  var height = Module._get_display_height();

  //  Resize the canvas to PineTime dimensions (240 x 240)
  if (
    Module.canvas.width != width * DISPLAY_SCALE ||
    Module.canvas.height != height * DISPLAY_SCALE
  ) {
    Module.canvas.width = width * DISPLAY_SCALE;
    Module.canvas.height = height * DISPLAY_SCALE;
  }

Fetch HTML Canvas

We fetch the HTML Canvas...

  //  Fetch the canvas pixels
  var ctx = Module.canvas.getContext('2d');
  var imageData = ctx.getImageData(0, 0, width * DISPLAY_SCALE, height * DISPLAY_SCALE);
  var data = imageData.data;

Copy WebAssembly Display Buffer to HTML Canvas

We copy the pixels from the WebAssembly Display Buffer to the HTML Canvas (which uses 24-bit RGBA format)...

  const DISPLAY_SCALE = 2;  //  Scale the canvas width and height
  const DISPLAY_BYTES_PER_PIXEL = 4;  //  4 bytes per pixel: RGBA

  //  Copy the pixels from the WebAssembly Display Buffer to the canvas
  var addr = Module._get_display_buffer();
  Module.print(`In JavaScript: get_display_buffer() returned ${toHex(addr)}`);          
  for (var y = 0; y < height; y++) {
    //  Scale the pixels vertically to fill the canvas
    for (var ys = 0; ys < DISPLAY_SCALE; ys++) {
      for (var x = 0; x < width; x++) {
        //  Copy from src to dest with scaling
        const src = ((y * width) + x) * DISPLAY_BYTES_PER_PIXEL;
        const dest = ((((y * DISPLAY_SCALE + ys) * width) + x) * DISPLAY_BYTES_PER_PIXEL) 
          * DISPLAY_SCALE;
        //  Scale the pixels horizontally to fill the canvas
        for (var xs = 0; xs < DISPLAY_SCALE; xs++) {
          const dest2 = dest + xs * DISPLAY_BYTES_PER_PIXEL;
          //  Copy 4 bytes: RGBA
          for (var b = 0; b < DISPLAY_BYTES_PER_PIXEL; b++) {
            data[dest2 + b] = Module.HEAPU8[addr + src + b];
          }
        }
      }
    }
  }

Note that JavaScript is allowed to read and write to WebAssembly Memory (treating it like a JavaScript array of bytes in Module.HEAPU8[]). But WebAssembly can't access any JavaScript Memory.

That's why we designed the Display Buffer Functions to manipulate WebAssembly Memory.

Paint the HTML Canvas

Finally we update the HTML Canvas...

  //  Paint the canvas
  ctx.putImageData(imageData, 0, 0);
}

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README.md

README.md

WebAssembly Simulator for Rust on Mynewt with LVGL

Features

Upcoming Features

References

How To Build The Simulator

Install emscripten on Windows Without WSL

Install emscripten on macOS

Install emscripten on Ubuntu x64 and Windows WSL

Install emscripten on Arch Linux / Manjaro Arm64

For emscripten version 1.40.x and newer

For emscripten version 1.39.x and binaryen version 95 only

emcc Error: Unexpected binaryen version

emcc Error: stackSave already exists

How It Works

Rename the HTML files

Dump the WebAssembly modules

Patch for `cty` crate

Rust on Mynewt Sandbox

Exported Functions

Clock Functions

Display Functions

Display Buffer Functions

Test Functions

Other Functions

Simulator JavaScript

Initialise WebAssembly

Initialise LVGL Display

Create Watch Face

Update Watch Face Time

Redraw Watch Face

Render LVGL Widgets to WebAssembly Display Buffer

Resize HTML Canvas

Fetch HTML Canvas

Copy WebAssembly Display Buffer to HTML Canvas

Paint the HTML Canvas

Files

README.md

Latest commit

History

README.md

File metadata and controls

WebAssembly Simulator for Rust on Mynewt with LVGL

Features

Upcoming Features

References

How To Build The Simulator

Install emscripten on Windows Without WSL

Install emscripten on macOS

Install emscripten on Ubuntu x64 and Windows WSL

Install emscripten on Arch Linux / Manjaro Arm64

For emscripten version 1.40.x and newer

For emscripten version 1.39.x and binaryen version 95 only

emcc Error: Unexpected binaryen version

emcc Error: stackSave already exists

How It Works

Rename the HTML files

Dump the WebAssembly modules

Patch for cty crate

Rust on Mynewt Sandbox

Exported Functions

Clock Functions

Display Functions

Display Buffer Functions

Test Functions

Other Functions

Simulator JavaScript

Initialise WebAssembly

Initialise LVGL Display

Create Watch Face

Update Watch Face Time

Redraw Watch Face

Render LVGL Widgets to WebAssembly Display Buffer

Resize HTML Canvas

Fetch HTML Canvas

Copy WebAssembly Display Buffer to HTML Canvas

Paint the HTML Canvas

Patch for `cty` crate