blog post about new web graphics

blog/_posts/2023-06-05-web-based-graphics-default.md

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+---
+title: "Interactive, web-based canvas is now the default in ROOT"
+layout: archive
+author: Sergey Linev
+---
+
+After a long period of development and testing we decided to switch to the web-based `TCanvas`
+implementation by default in the ROOT master version. It has been present in the ROOT for a
+while (since 2017) and used already in the web-based TBrowser, which you have probably seen already.
+
+What has changed ? Now when starting a ROOT session and displaying any object in `TCanvas`,
+the default system web browser will start and the object will be drawn there using the JavaScript
+ROOT functionality. The look and feel for basic objects, like histograms and graphs, will not
+change much – all the drawing options and styles are supported as in the original graphics.
+You can compare the two following screen shots made with the same macro – one is original
+ROOT graphics, other is web-based one.
+
+<center>
+<img src="{{'/assets/images/plain_canvas.png' | relative_url}}" alt="Plain Canvas" style="width: 80%" width="1600" height="749" />
+<img src="{{'/assets/images/web_canvas.png' | relative_url}}" alt="Web Canvas" style="width: 80%" width="1600" height="749" />
+</center>
+
+What are the benefits of using the web-based canvas?
+ 1.  The painting is fully decoupled from the main program and runs asynchronously.
+ 2.  As the display is just normal web browser, the painting is the same on all platforms
+     supported by ROOT natively as Linux/Mac/Windows, but also on many others where ROOT may
+     not run at all – like all kinds of smartphones and tablets.
+ 3.  Threads safety - The object painting and the interactivity happen in the web browser and don't
+     depend on the application state. With some little configuration efforts one can run different
+     canvases from different threads.
+ 4.  Free from `gPad` problematic - lots of interactivity in original ROOT graphics were built
+     around this global pointer. This made it difficult to use several canvases at the same time.
+ 5.  The Web is a very natural way for implementing remote displays. Instead of struggling with
+     remote X11 one can just use a local web browser accessing remote applications through
+     http. To ease configuration of `ssh` tunnels, we provide a simple `rootssh` utility which
+     fully automates the configuration of such tunnels.
+ 6.  One can use QWebEngine (Qt5 and Qt6) to implement a fully local display without any http
+     server in-between. This allows embedding any kind of ROOT web-based widgets into Qt
+     applications on all platforms.
+
+What about image production in batch?
+For the moment we keep the old functionality, like when running ROOT with the `-b` flag, for image
+production. Web-based canvas will be used for PNG/JPEG/SVG images creation by adding `--web`
+flag when running ROOT. While image generation involves running web browsers in headless
+mode, it takes time – approximately 1 second per image. We plan to provide a special API to
+produce many images with one call – which should significantly improve performance.
+
+What are drawbacks?
+Probably you'll encounter minimal differences between drawing with native ROOT graphics and in
+the web browsers. We do our best to make them similar as much as possible – and you can help
+us by reporting the problems. Probably some very special usages of `TExec` objects (do you know about them?)
+will not work as expected in web-based canvases. With a little help from us this can be
+fixed and adjusted. For sophisticated use-cases with complex user-defined objects one could
+consider implementing JavaScript-based painters for them.
+
+We encourage all users to try this functionality and give us the feedback!