add optional speed chart in preview mode

src/mode/fdm/prepare.js

@@ -397,6 +397,10 @@
         }
     }
 
+    FDM.colorFunc = function(rate) {
+        return hsv2rgb({h: rate, s:1, v:0.75}, true);
+    };
+
     FDM.prepareRender = function(levels, update, options) {
         const opts = options || {};
         const tools = opts.tools || {};
@@ -410,6 +414,9 @@
             return level.map(o => o.speed || 0).reduce((a, v) => Math.max(a,v));
         }).reduce((a, v) => Math.max(a, v)) + 1;
 
+        // for reporting
+        self.worker.print.maxSpeed = maxspd - 1;
+
         let lastOut = null;
         let current = null;