I like it and there are some plugins to use as well.
First results can be achieved very quickly, but if you want to change further specific things, it’s getting difficult with the various objects.

@sdetweil do you know of a complete set of options for chartjs? I find the documentation a bit too short and confusing.

I have no idea what you just said but I upvoted your post anyway. :-)

• reduce number of data points, by decimation (using 1 point of every 5) to get to 800 points. See info once every 5th minutes, vs once a minute
• build 800 point data from in memory CSV (api sends back csv data) by looking from NOW (end) til previous (backwards) which reduces the number of lines of data processed from 14000 to 4000 (configurable number of days for chart)
• create a color gradient table start-end: color, start-end:color2… to draw multiple colors on chart, as part of the data selection in 1 and 2 above… this make the processor O(1) (single pass), instead of O(4)

performance is much improved…
prior, 4000 points, elapsed time for 2 charts, 39 seconds. now 3.5 seconds (odroid). pi crashed with 4000 points at 4 minutes elapsed… now just about 4.5 seconds

still pretty reasonable performance.

update once every 5 minutes, or when come back from sleeping (no updates while MM is asleep).

here is the chartjs code
i have an structure, with arrays of points (by the sensor value), javascript Date, and value.
there are also arrays that contain the axis labels.

make div for chart
	var c = document.createElement("div");	
	c.style.width=self.config.width+"px";
  	c.style.height=self.config.height+"px";
	if(!self.config.stacked)
	   c.style.display='inline-block';
	self.wrapper.appendChild(c);

        canvas= document.createElement("canvas");
 	canvas.id="myChart"+this_pin;
        c.appendChild(canvas);

for(var pin_index=0; 
      pin_index < self.config.Pins.length;  (how do you do less than in markup?, space after < )
      pin_index++)
{
var this_pin=self.config.Pins[pin_index];

       self.charts[pin_index] = new Chart(canvas, {
              type: 'line',
              showLine: true,							
              data: {
                datasets: [
                  {
		    xAxisID: 'dates',
                    data: self.data[this_pin], 
                    fill:true,
                    borderColor: '#2196f3', 
   		    backgroundColor: '#2196f3', 
	             },
                ]
              },
              options:	 { 
			legend: { display: false},
			tooltips: {
			    enabled: false,
			    displayColors: false
			  },
			responsive: false,
			elements: {
			    point: { radius: 0 },
			    line: {
        		        tension: 0, // disables bezier curves
			     }
        		},
                scales: {
                  xAxes: [{
			id: 'dates',
                    type: 'time',
			distribution: 'linear',
                    scaleLabel: {
                        display: true,
                        labelString: self.config.labels[pin_index]+" - last "+self.config.dayrange+" days",
			fontColor: 'white'
                    },
			gridLines: {
				display: false,
				zeroLineColor: '#ffcc33'
			},
  		        time: {
      		              unit: 'minute'
          		      },
			bounds: 'data',
                    ticks: {
			display: false ,
			maxRotation: 90,
			source: 'data',
			maxTicksLimit: self.data[this_pin].length,                    },
                  }],
                  yAxes: [{
                        display: true,
                        scaleLabel: {
                            display: true,
                            labelString: self.config.yaxis_legend[pin_index],
			    fontColor: 'white'
                        },
			gridLines: {
			   display: true,
			   color: "#FFFFFF",
			   zeroLineColor: '#ffcc33',
			   fontColor: 'white',									 
                           scaleFontColor: 'white',
			},

                    ticks: {
			beginAtZero: true,
			source: 'data',
                        min: 0,
			fontColor: 'white'
                    },
                    }]
                },
              }
            });
}

two charts upper right

two charts closer view

one chart

while I had an array for time based points, ONE element in the array was JUST a single value.

this caused the charting tool to act weird…

fixing the one data point resolved the issue…

now, I want to change the color of the fill area under certain conditions (low reservoir, or constant running water) to alert about trouble to be resolved…looks like that is some custom extension i have to write…

MMM-chart,

thanks… my data does not come back in JSON… but as CSV. with a unix milliseconds timestamp.

one data set is a float value (could be truncated to int), one is an int.

i have made some progress. the chart appears and has the right axis labels and values…

the chart itself is drawn wrong… with the jagged line across the x-axis at the right Y-axis height, being drawn vertically on the right edge of the chart, top to bottom…

Mmm-rainfc at git