Flot: dramatic performance improvements

Redraws graphs in place instead of recomputing them from scratch on each
new time index.

lib/riemann/dash/public/views/flot.js

@@ -49,7 +49,8 @@
 
         this.clockSub = clock.subscribe(function(t) {
           self.trimData(t);
-          self.setupGraph(t);
+          self.updateTime(t);
+//          self.setupGraph(t);
         });
 
         // Subscribe to our query
@@ -70,7 +71,10 @@
     FlotView.prototype.setupGraph = function(t) {
       if (this.container.width() === 0 ||
           this.container.height() === 0) {
+            if (this.graph != null) {
+              this.graph.shutdown();
               this.graph = null;
+            }
             return;
       }
 
@@ -100,6 +104,21 @@
       });
     };
 
+    // Called as the clock advances to new times.
+    FlotView.prototype.updateTime = function(t) {
+      if (this.graph == null) {
+        console.log("first initialization");
+        this.setupGraph(t);
+        return;
+      }
+
+      var axis = this.graph.getOptions().xaxes[0];
+      axis.min = t - this.timeRange;
+      axis.max = t;
+      this.graph.setupGrid();
+      this.graph.draw();
+    }
+
     // Re-order the data list and series index to be in sorted order by label. 
     FlotView.prototype.resortSeries = function() {
       // Shorten labels