create-gojs-kit
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A CLI for downloading GoJS samples, extensions, and docs
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<div class="px-4 pb-16 w-full overflow-hidden prose">
<h1>Creating Images on the Server</h1>
<p>It may be useful for many applications to create images of Diagrams with <b>GoJS</b>, and this page details some of the options for such a task.</p>
<h2 id="Puppeteer">Puppeteer</h2>
<p>
<a href="https://github.com/GoogleChrome/puppeteer">Puppeteer</a> is a Node library which provides a high-level API to control headless Chrome. We can use it
to create images server-side. If you have Node and npm installed you can install it with <code>npm install puppeteer</code>.
</p>
<p>
The following code is a small example using Puppeteer. If you saved the JavaScript as <code>puppet.js</code> and run it with node (<code
>node createImage.js</code
>) it demonstrate creating two images: One from the Diagram called <code>gojs-screenshot.png</code> and one of the HTML page called
<code>page-screenshot.png</code>. The Diagram code in the sample is the same as that in the <a href="../samples/minimal.html">Minimal sample</a>.
</p>
<pre class="lang-js"><code>
// This example loads the GoJS library then adds HTML from scratch and evaluates some JavaScript,
// then creates a screenshot of Diagram with makeImageData, plus a screenshot of the page.
const puppeteer = require('puppeteer');
const fs = require('fs');
const parseDataUrl = dataUrl => {
const matches = dataUrl.match(/^data:(.+);base64,(.+)$/);
if (matches.length !== 3) {
throw new Error('Could not parse data URL.');
}
return { mime: matches[1], buffer: Buffer.from(matches[2], 'base64') };
};
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
// Point to a version of go.js, either a local file or one on the web at a CDN
await page.addScriptTag({
url: 'https://cdn.jsdelivr.net/npm/gojs'
// path: '../../release/go.js'
});
// Create HTML for the page:
page.setContent('<div id="myDiagramDiv" style="border: solid 1px black; width:400px; height:400px"></div>');
// Set up a Diagram, and return the result of makeImageData:
const imageData = await page.evaluate(() => {
const myDiagram = new go.Diagram("myDiagramDiv", {
"animationManager.isEnabled": false,
"undoManager.isEnabled": true // enable undo & redo
});
// define a simple Node template
myDiagram.nodeTemplate =
new go.Node("Auto")
.add( // the Shape will go around the TextBlock
new go.Shape("RoundedRectangle", { strokeWidth: 0 })
.bind("fill", "color"),
new go.TextBlock({ margin: 8 })
.bind("text", "key")
);
myDiagram.model = new go.GraphLinksModel(
[
{ key: "Alpha", color: "lightblue" },
{ key: "Beta", color: "orange" },
{ key: "Gamma", color: "lightgreen" },
{ key: "Delta", color: "pink" }
],
[
{ from: "Alpha", to: "Beta" },
{ from: "Alpha", to: "Gamma" },
{ from: "Beta", to: "Beta" },
{ from: "Gamma", to: "Delta" },
{ from: "Delta", to: "Alpha" }
]);
return myDiagram.makeImageData();
});
// Output the GoJS makeImageData as a .png:
const { buffer } = parseDataUrl(imageData);
fs.writeFileSync('diagram-screenshot.png', buffer, 'base64');
// Output a page screenshot
await page.screenshot({ path: 'page-screenshot.png' });
await browser.close();
})();
</code></pre>
<p>You can also use Puppeteer to fetch live HTML pages and do the same operations:</p>
<pre class="lang-js"><code>
// This example loads a web page with a GoJS diagram,
// then creates a screenshot of the Diagram with makeImageData, plus a screenshot of the page.
const puppeteer = require('puppeteer');
const fs = require('fs');
const parseDataUrl = dataUrl => {
const matches = dataUrl.match(/^data:(.+);base64,(.+)$/);
if (matches.length !== 3) {
throw new Error('Could not parse data URL.');
}
return { mime: matches[1], buffer: Buffer.from(matches[2], 'base64') };
};
(async () => {
const browser = await puppeteer.launch();
const page = await browser.newPage();
// This does not have to be a page on the web, it can be a localhost page, or file://
await page.goto('https://gojs.net/samples/orgChartEditor.html', {
waitUntil: 'networkidle2' // ensures images are loaded
});
const imageData = await page.evaluate(() => {
window.myDiagram.animationManager.stopAnimation();
return window.myDiagram.makeImageData({
background: window.myDiagram.div.style.backgroundColor
});
});
// Output the GoJS makeImageData as a .png:
const { buffer } = parseDataUrl(imageData);
fs.writeFileSync('diagram-screenshot.png', buffer, 'base64');
// Output a page screenshot
await page.screenshot({ path: 'page-screenshot.png' });
await browser.close();
})();
</code></pre>
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