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Crystal Webview

Crystal language bindings for zserge's Webview which is an excellent cross-platform single-header webview library for C/C++ using Gtk, Cocoa, or MSHTML/Edge, depending on the host OS.

Webview relys on default rendering engine of host Operating System, thus binaries generated with this Shard will be much more leaner as compared to Electron which bundles Chromium with each distribution.

This shard supports two-way bindings between Crystal and JavaScript. You can invoke JS code via Webview::Webview#eval and calling Crystal code from JS is done via WebView::Webview#bind (refer to Examples 3 & 4 for samples on how to invoke Crystal functions from JS).

Webview-supported platforms and the engines you can expect to render your application content are as follows:

Operating System Browser Engine Used
macOS Cocoa, WebKit
Linux GTK 3, WebKitGTK
Windows Windows API, WebView2

Pre-requisite

If you're planning on targeting Linux or BSD you must ensure that WebKit2GTK is already installed and available for discovery via the pkg-config command.

Debian-based systems:

  • Packages:
    • Development: apt install libgtk-3-dev libwebkit2gtk-4.0-dev
    • Production: apt install libgtk-3-0 libwebkit2gtk-4.0-37

BSD-based systems:

  • FreeBSD packages: pkg install webkit2-gtk3
  • Execution on BSD-based systems may require adding the wxallowed option (see mount(8)) to your fstab to bypass W^X memory protection for your executable. Please see if it works without disabling this security feature first.

Microsoft Windows:

  • You should have Visual C++ Build tools already as it's a pre-requisite for crystal compiler
  • git clone https://github.com/webview/webview to get WebView sources
  • webview\script\build.bat to compile them (it will download required nuget package)
  • copy webview\dll\x64\webview.lib to <your crystal installation>\lib
  • copy webview\dll\x64\webview.dll to directory with your program

Installation

  1. Add the dependency to your shard.yml:

    dependencies:
  webview:
    github: naqvis/webview

  2. Run shards install

Usage

Example 1: Loading URL

require "webview"

wv = Webview.window(640, 480, Webview::SizeHints::NONE, "Hello WebView", "http://crystal-lang.org")
wv.run
wv.destroy

Example 2: Loading HTML

require "webview"

html = <<-HTML
<!DOCTYPE html><html lang="en-US">
<head>
<title>Hello,World!</title>
</head>
<body>
<div class="container">
<header>
	<!-- Logo -->
   <h1>City Gallery</h1>
</header>
<nav>
  <ul>
    <li><a href="/London">London</a></li>
    <li><a href="/Paris">Paris</a></li>
    <li><a href="/Tokyo">Tokyo</a></li>
  </ul>
</nav>
<article>
  <h1>London</h1>
  <img src="pic_mountain.jpg" alt="Mountain View" style="width:304px;height:228px;">
  <p>London is the capital city of England. It is the most populous city in the  United Kingdom, with a metropolitan area of over 13 million inhabitants.</p>
  <p>Standing on the River Thames, London has been a major settlement for two millennia, its history going back to its founding by the Romans, who named it Londinium.</p>
</article>
<footer>Copyright &copy; W3Schools.com</footer>
</div>
</body>
</html>
HTML

wv = Webview.window(640, 480, Webview::SizeHints::NONE, "Hello WebView")
wv.html = html
wv.run
wv.destroy

Example 3: Calling Crystal code from JavaScript

require "webview"

html = <<-HTML
<!doctype html>
<html>
  <body>hello</body>
  <script>
    window.onload = function() {
      document.body.innerText = "Javascript calling Crystal code";
      noop().then(function(res) {
        console.log('noop res', res);
        add(1, 2).then(function(res) {
          console.log('add res', res);
        });
      });
    };
  </script>
</html>
HTML

wv = Webview.window(640, 480, Webview::SizeHints::NONE, "Hello WebView", true)
wv.html = html
wv.bind("noop", Webview::JSProc.new { |a|
  pp "Noop called with arguments: #{a}"
  JSON::Any.new("noop")
})

wv.bind("add", Webview::JSProc.new { |a|
  pp "add called with arguments: #{a}"
  ret = 0_i64
  a.each do |v|
    ret += v.as_i64
  end
  JSON::Any.new(ret)
})


wv.run
wv.destroy

Example 4: Calling Crystal code from JavaScript and executing JavaScript from Crystal

require "webview"

html = <<-HTML
<!DOCTYPE html><html lang="en-US">
<head>
<title>Hello,World!</title>
</head>
<body>
  <button onClick="add(document.body.children.length)">Add</button>
</body>
</html>
HTML


inject = <<-JS
  elem = document.createElement('div');  
  elem.innerHTML = "hello webview %s";
  document.body.appendChild(elem);
JS

wv = Webview.window(640, 480, Webview::SizeHints::NONE, "Hello WebView", true)
wv.html = html

wv.bind("add", Webview::JSProc.new { |n|
  wv.eval(sprintf(inject, n))
  JSON::Any.new(nil)
})

wv.run
wv.destroy

Example 5: Running your web app in another thread

Thread.new do
  get "/" do
    "hello from kemal"
  end
  Kemal.run
end

wv = Webview.window(640, 480, Webview::SizeHints::NONE, "WebView with local webapp!", "http://localhost:3000")
wv.run
wv.destroy

App Distribution

Distribution of your app is outside the scope of this library but we can give some pointers for you to explore.

macOS Application Bundle

On macOS you would typically create a bundle for your app with an icon and proper metadata.

A minimalistic bundle typically has the following directory structure:

example.app                 bundle
└── Contents
    ├── Info.plist          information property list
    ├── MacOS
    |   └── example         executable
    └── Resources
        └── example.icns    icon

Read more about the structure of bundles at the Apple Developer site.

Tip: The png2icns tool can create icns files from PNG files. See the icnsutils package for Debian-based systems.

Windows Apps

You would typically create a resource script file (*.rc) with information about the app as well as an icon. Since you should have MinGW-w64 readily available then you can compile the file using windres and link it into your program. If you instead use Visual C++ then look into the Windows Resource Compiler.

The directory structure could look like this:

my-project/
├── icons/
|   ├── application.ico
|   └── window.ico
├── basic.cc
└── resources.rc

resources.rc:

100 ICON "icons\\application.ico"
32512 ICON "icons\\window.ico"

Note: The ID of the icon resource to be used for the window must be 32512 (IDI_APPLICATION).

Limitations

Browser Features

Since a browser engine is not a full web browser it may not support every feature you may expect from a browser. If you find that a feature does not work as expected then please consult with the browser engine's documentation and open an issue on webview library if you think that the library should support it.

For example, the webview library does not attempt to support user interaction features like alert(), confirm() and prompt() and other non-essential features like console.log().

Contributing

  1. Fork it (https://github.com/naqvis/webview/fork)
  2. Create your feature branch (git checkout -b my-new-feature)
  3. Commit your changes (git commit -am 'Add some feature')
  4. Push to the branch (git push origin my-new-feature)
  5. Create a new Pull Request

Contributors