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Generate math PNGs on iOS with KaTeX (Xcode Playground)
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| import UIKit | |
| import WebKit | |
| import PlaygroundSupport | |
| var html = """ | |
| <!DOCTYPE html> | |
| <html> | |
| <head> | |
| <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/katex@0.11.1/dist/katex.min.css" integrity="sha384-zB1R0rpPzHqg7Kpt0Aljp8JPLqbXI3bhnPWROx27a9N0Ll6ZP/+DiW/UqRcLbRjq" crossorigin="anonymous"> | |
| <script src="https://cdn.jsdelivr.net/npm/katex@0.11.1/dist/katex.min.js" integrity="sha384-y23I5Q6l+B6vatafAwxRu/0oK/79VlbSz7Q9aiSZUvyWYIYsd+qj+o24G5ZU2zJz" crossorigin="anonymous"></script> | |
| <style type="text/css"> | |
| body { background: transparent; margin: 0; font-size: 300%; } | |
| .katex-display, .katex, .katex-html { display: inline !important; } | |
| #math { float: left; } | |
| </style> | |
| </head> | |
| <body> | |
| <span id="math"></span> | |
| </body> | |
| <script> | |
| function getMathElement() { | |
| return document.getElementById('math'); | |
| } | |
| function render(math) { | |
| try { | |
| katex.render(math, getMathElement()); | |
| return true; | |
| } catch { | |
| return false; | |
| } | |
| } | |
| function bounds() { | |
| return getMathElement().getBoundingClientRect().toJSON(); | |
| } | |
| </script> | |
| </html> | |
| """ | |
| class NavDelegate : NSObject, WKNavigationDelegate { | |
| func webView(_ webView: WKWebView, didFinish navigation: WKNavigation!) { | |
| renderMath(webView, math: "c = \\pm\\sqrt{a^2 + b^2}") | |
| } | |
| } | |
| func renderMath(_ webView: WKWebView, math: String) { | |
| let escaped = math.replacingOccurrences(of: "\\", with: "\\\\") | |
| web.evaluateJavaScript("render('\(escaped)')") { result, error in | |
| guard let result = result as? Bool else { | |
| dump(error) | |
| return | |
| } | |
| if result { | |
| takeSnapshot(webView) | |
| } else { | |
| print("KaTeX error") | |
| } | |
| } | |
| } | |
| func takeSnapshot(_ webView: WKWebView) { | |
| webView.evaluateJavaScript("bounds()") { bbox, error in | |
| guard let bbox = bbox as? [String:Any] else { | |
| dump(error) | |
| return | |
| } | |
| let x = (bbox["left"] as! NSNumber).intValue | |
| let y = (bbox["top"] as! NSNumber).intValue | |
| let w = (bbox["width"] as! NSNumber).intValue | |
| let h = (bbox["height"] as! NSNumber).intValue | |
| let rect = CGRect(x: x, y: y, width: w, height: h) | |
| print("Crop rect: \(rect)") | |
| let snapConfig = WKSnapshotConfiguration() | |
| snapConfig.rect = rect | |
| snapConfig.afterScreenUpdates = true | |
| webView.takeSnapshot(with: snapConfig) { image, error in | |
| guard let image = image else { | |
| dump(error) | |
| return | |
| } | |
| saveImage(image) | |
| } | |
| } | |
| } | |
| func saveImage(_ image: UIImage) { | |
| guard let data = image.pngData() else { | |
| print("Couldn't get data") | |
| return | |
| } | |
| let url = URL(fileURLWithPath: "math.png") | |
| print("Saving to \(url.absoluteString)") | |
| try! data.write(to: url) | |
| } | |
| let frame = CGRect(x: 0, y: 0, width: 600, height: 800) | |
| let web = WKWebView(frame: frame) | |
| web.isOpaque = false | |
| let delegate = NavDelegate() | |
| web.navigationDelegate = delegate | |
| web.loadHTMLString(html, baseURL: nil) | |
| PlaygroundPage.current.liveView = web |
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