mirror of
https://github.com/scratchfoundation/scratch-vm.git
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115 lines
3.7 KiB
Markdown
115 lines
3.7 KiB
Markdown
## scratch-vm
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#### Scratch VM is a library for representing, running, and maintaining the state of computer programs written using [Scratch Blocks](https://github.com/LLK/scratch-blocks).
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[](https://travis-ci.org/LLK/scratch-vm)
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[](https://coveralls.io/github/LLK/scratch-vm?branch=develop)
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[](https://david-dm.org/LLK/scratch-vm)
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[](https://david-dm.org/LLK/scratch-vm#info=devDependencies)
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## Installation
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This requires you to have Git and Node.js installed.
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In your own node environment/application:
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```bash
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npm install https://github.com/LLK/scratch-vm.git
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```
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If you want to edit/play yourself:
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```bash
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git clone https://github.com/LLK/scratch-vm.git
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cd scratch-vm
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npm install
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```
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## Development Server
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This requires Node.js to be installed.
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For convenience, we've included a development server with the VM. This is sometimes useful when running in an environment that's loading remote resources (e.g., SVGs from the Scratch server).
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## Running the Development Server
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Open a Command Prompt or Terminal in the repository and run:
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```bash
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npm start
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```
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Or on Windows:
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```bash
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StartServerWindows.bat
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```
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## Playground
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To run the Playground, make sure the dev server's running and go to [http://localhost:8080/](http://localhost:8080/) - you will be directed to the playground, which demonstrates various tools and internal state.
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## Standalone Build
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```bash
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make build
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```
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```html
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<script src="/path/to/vm.js"></script>
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<script>
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var vm = new window.VirtualMachine();
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// do things
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</script>
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```
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## How to include in a Node.js App
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For an extended setup example, check out the /playground directory, which includes a fully running VM instance.
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```js
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var VirtualMachine = require('scratch-vm');
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var vm = new VirtualMachine();
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// Block events
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workspace.addChangeListener(vm.blockListener);
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// Run threads
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vm.start();
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```
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## Abstract Syntax Tree
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#### Overview
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The Virtual Machine constructs and maintains the state of an [Abstract Syntax Tree](https://en.wikipedia.org/wiki/Abstract_syntax_tree) (AST) by listening to events emitted by the [scratch-blocks](https://github.com/LLK/scratch-blocks) workspace via the `blockListener`. Each target (code-running object, for example, a sprite) keeps an AST for its blocks. At any time, the current state of an AST can be viewed by inspecting the `vm.runtime.targets[...].blocks` object.
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#### Anatomy of a Block
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The VM's block representation contains all the important information for execution and storage. Here's an example representing the "when key pressed" script on a workspace:
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```json
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{
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"_blocks": {
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"Q]PK~yJ@BTV8Y~FfISeo": {
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"id": "Q]PK~yJ@BTV8Y~FfISeo",
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"opcode": "event_whenkeypressed",
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"inputs": {
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},
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"fields": {
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"KEY_OPTION": {
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"name": "KEY_OPTION",
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"value": "space"
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}
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},
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"next": null,
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"topLevel": true,
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"parent": null,
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"shadow": false,
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"x": -69.333333333333,
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"y": 174
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}
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},
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"_scripts": [
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"Q]PK~yJ@BTV8Y~FfISeo"
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]
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}
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```
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## Testing
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```bash
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make test
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```
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```bash
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make coverage
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```
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## Donate
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We provide [Scratch](https://scratch.mit.edu) free of charge, and want to keep it that way! Please consider making a [donation](https://secure.donationpay.org/scratchfoundation/) to support our continued engineering, design, community, and resource development efforts. Donations of any size are appreciated. Thank you!
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