Introduce build3d for TCanvas

Author: linev

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;