Implement build3d for TCanvas

demo/build3d.htm

@@ -114,7 +114,9 @@
       let server = 'https://root.cern/js/files/',
           filename = server + 'hsimple.root',
           filename2 = server + 'graph2d.root',
-          filename3 = server + 'geom/simple_alice.json.gz';
+          filename3 = server + 'geom/simple_alice.json.gz',
+          filename4 = server + 'tutorials_fit.root';
+
 
       let file = await openFile(filename);
       let hist2 = await file.readObject('hpxpy');
@@ -126,9 +128,10 @@
 
       await create3d(hist3, 'box3', -150, '#color[2]{TH3} #color[4]{box} plot');
 
-      let hist1 = await file.readObject('hpx');
+      let file4 = await openFile(filename4);
+      let canv = await file4.readObject('fit2a');
 
-      await create3d(hist1, 'lego2', 400, '#color[2]{TH1} #color[4]{lego} plot');
+      await create3d(canv, '', 400, '#color[2]{TCanvas} with #color[4]{TH2} and #color[4]{TF2}');
 
       let geom = await httpRequest(filename3, 'object');
       await create3d(geom, '', -400, '#color[2]{Geometry} build', 0.2);

modules/draw/TTextPainter.mjs

@@ -15,6 +15,11 @@ class TTextPainter extends ObjectPainter {
             pp = this.getPadPainter(),
             fp = this.getFramePainter(),
             is_url = text.fName.startsWith('http://') || text.fName.startsWith('https://');
+
+      // special handling of dummy frame painter
+      if (fp?.getDrawDom() === null)
+         return this;
+
       let fact = 1, use_frame = false;
 
       this.createAttText({ attr: text });

modules/gpad/TCanvasPainter.mjs

@@ -936,6 +936,20 @@ class TCanvasPainter extends TPadPainter {
       this.getWebsocket()?.resizeWindow(fullW, fullH);
    }
 
+   /** @summary create three.js object for TCanvas */
+   static async build3d(can, opt, get_painter) {
+      const painter = new TCanvasPainter(null, can, opt, true);
+      painter.checkSpecialsInPrimitives(can, true);
+
+      const fp = new TFramePainter(null, null);
+      // return dummy frame painter as result
+      painter.getFramePainter = () => fp;
+
+      return painter.drawPrimitives().then(() => {
+         return get_painter ? painter : fp.create3DScene(-1, true);
+      });
+   }
+
    /** @summary draw TCanvas */
    static async draw(dom, can, opt) {
       const nocanvas = !can;

modules/hist/TPavePainter.mjs

@@ -167,6 +167,11 @@ class TPavePainter extends ObjectPainter {
             opt = this.getPaveDrawOption().toUpperCase(),
             fp = this.getFramePainter(), pp = this.getPadPainter(),
             pad = pp.getRootPad(true);
+
+      // special handling of dummy frame painter
+      if (fp?.getDrawDom() === null)
+         return this;
+
       let interactive_element, width, height;
 
       if (pt.fInit === 0) {