Noah Petherbridge af67b20d9b Initial WebAssembly Build Target

* Initial WebAssembly build target for Doodle in the wasm/ folder.
* Add a new render.Engine implementation, lib/render/canvas that uses
  the HTML 5 Canvas API instead of SDL2 for the WebAssembly target.
  * Ported the basic DrawLine(), DrawBox() etc. functions from SDL2 to
    Canvas context2d API.
  * Fonts are handled with CSS embedded fonts named after the font
    filename and defined in wasm/index.html
* `make wasm` builds the WASM program, and `make wasm-serve` runs a dev
  Go server that hosts the WASM file for development. The server also
  watches the dev tree for *.go files and rebuilds the WASM binary
  automatically on change.
* This build "basically" runs the game. UI and fonts all work and mouse
  movements and clicks are detected. No wallpaper support yet or texture
  caching (which will crash the game as soon as you click and draw a
  pixel in your map!)

2019-06-26 18:40:40 -07:00

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WebAssembly Port

Build and Test

Change to the wasm/ folder and type make to build doodle.wasm

To test it with a local Go server, cd to the wasm/ folder and run go run server.go and visit http://localhost:8080/

Copy the fonts and assets folders from the project root to the wasm/ directory so they're available over HTTP.

wasm_exec.js

To update the wasm_exec.js to match your version of Go:

# Fedora: install golang-misc
sudo dnf install golang-misc

# Copy the wasm_exec.js
cp $(go env GOROOT)/misc/wasm/wasm_exec.js ./

Font Support

Fonts are implemented as CSS embedded fonts configured in wasm/index.html

The font family name should match the filename, sans .ttf extension, for example "DejaVuSans-Bold". Doodle's internal logic converts a FontFilename string like "./fonts/DejaVuSans.ttf" into the base name to use as the font family. It also has fallbacks for sans-serif and serif in case of any problems.

Known Bugs and Limitations

github.com/kirsle/golog
- The detection of an interactive terminal is broken in WASM.
- terminal.IsTerminal(int(os.Stdout.Fd()))
- As a workaround, comment it out and hardcode to false
Userdir
- For WASM we'll want to use localStorage to store user drawings instead of the userdir.
Wallpaper support
- WASM can't use os.Open to read the wallpaper image, so will need another method to load the image.
- Texture caching support isn't implemented yet to hold the four corner textures of a wallpaper.
- As a workaround, added a wallpaper.ready boolean and relevant functions exit early for WASM so wallpapers don't render at all.

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