Add support for markers

Author: rs

README.md

@@ -9,11 +9,10 @@ Above capture is jplot monitoring a Go service's [expvar](https://golang.org/pkg
 
 ```
 jplot --url http://:8080/debug/vars \
-    memstats.HeapSys+memstats.HeapAlloc+memstats.HeapIdle \
+    memstats.HeapAlloc+memstats.HeapSys+memstats.HeapAlloc+memstats.HeapIdle+marker:counter:memstats.NumGC \
     counter:memstats.TotalAlloc \
     memstats.HeapObjects \
-    memstats.StackSys+memstats.StackInuse \
-    counter:memstats.NumGC
+    memstats.StackSys+memstats.StackInuse
 ```
 
 ## Install
@@ -70,20 +69,28 @@ jplot --url http://:8080/debug/vars mem.Heap+mem.Sys+mem.Stack counter:cpu.STime
 
 ![all](doc/all.png)
 
-See [gojq](github.com/elgs/gojq) for more details on the JSON query syntax.
+### Spec Syntax
+
+Each positional arguments given to jplot create a stacked graph with the specified values. To reference the values, use [gojq](github.com/elgs/gojq) JSON query syntax. Several value paths can be referenced for the same graph by using the `+` character to separate them.
+
+In addition, each value path can be prefixed with options separated from the path by a column. Several options can be used for the same command by separating them with a comma like so: `option1,option2:value.path`.
+
+Supported options are:
+* `counter`: Computes the difference with the last value. The value must increase monotonically.
+* `marker`: When the value is none-zero, a vertical line is drawn.
 
 ### Memstats
 
 Here is an example command to graph a Go program memstats:
 
 ```
 jplot --url http://:8080/debug/vars \
-    memstats.HeapSys+memstats.HeapAlloc+memstats.HeapIdle \
+    memstats.HeapAlloc+memstats.HeapSys+memstats.HeapAlloc+memstats.HeapIdle+marker:counter:memstats.NumGC \
     counter:memstats.TotalAlloc \
     memstats.HeapObjects \
-    memstats.StackSys+memstats.StackInuse \
-    counter:memstats.NumGC
+    memstats.StackSys+memstats.StackInuse
 ```
+
 ![all](doc/memstats.png)
 
 

doc/demo.gif

@@ -33,13 +33,14 @@ type field struct {
 	id      string
 	name    string
 	counter bool
+	marker  bool
 }
 
 func main() {
 	url := flag.String("url", "", "URL to fetch every second. Read JSON objects from stdin if not specified.")
 	steps := flag.Int("steps", 100, "Number of values to plot.")
 	width := flag.Int("width", 2500, "Canvas width")
-	height := flag.Int("height", 1300, "Canvas height")
+	height := flag.Int("height", 1400, "Canvas height")
 	dpi := flag.Float64("dpi", 220, "Canvas definition")
 	flag.Parse()
 
@@ -106,6 +107,20 @@ func parseSpec(args []string, width, height int, dpi float64) []graphSpec {
 		}
 		for j, name := range strings.Split(v, "+") {
 			var isCounter bool
+			var isMarker bool
+			n := strings.Split(name, ":")
+			for len(n) > 1 {
+				switch n[0] {
+				case "counter":
+					isCounter = true
+				case "marker":
+					isMarker = true
+				default:
+					log.Fatalf("Invalid field option: %s", n[0])
+				}
+				n = n[1:]
+			}
+			name = n[0]
 			if strings.HasPrefix(name, "counter:") {
 				isCounter = true
 				name = name[8:]
@@ -114,6 +129,7 @@ func parseSpec(args []string, width, height int, dpi float64) []graphSpec {
 				id:      fmt.Sprintf("%d.%d.%s", i, j, name),
 				name:    name,
 				counter: isCounter,
+				marker:  isMarker,
 			})
 		}
 		specs = append(specs, gs)
@@ -125,14 +141,23 @@ func render(specs []graphSpec, dp *data.Points) {
 	graphs := make([]chart.Chart, 0, len(specs))
 	for _, gs := range specs {
 		series := []chart.Series{}
+		markers := []chart.GridLine{}
 		for _, f := range gs.fields {
 			vals := dp.Get(f.id)
+			if f.marker {
+				for i, v := range vals {
+					if v > 0 {
+						markers = append(markers, chart.GridLine{Value: float64(i)})
+					}
+				}
+				continue
+			}
 			series = append(series, chart.ContinuousSeries{
 				Name:    fmt.Sprintf("%s: %s", f.name, siValueFormater(vals[len(vals)-1])),
 				YValues: vals,
 			})
 		}
-		graphs = append(graphs, graph(series, gs.width, gs.height, gs.dpi))
+		graphs = append(graphs, graph(series, markers, gs.width, gs.height, gs.dpi))
 	}
 	printGraphs(graphs)
 }
@@ -155,7 +180,7 @@ func reset() {
 }
 
 // graph generate a line graph with series.
-func graph(series []chart.Series, width, height int, dpi float64) chart.Chart {
+func graph(series []chart.Series, markers []chart.GridLine, width, height int, dpi float64) chart.Chart {
 	for i, s := range series {
 		if s, ok := s.(chart.ContinuousSeries); ok {
 			s.XValues = seq.Range(0, float64(len(s.YValues)-1))
@@ -194,6 +219,23 @@ func graph(series []chart.Series, width, height int, dpi float64) chart.Chart {
 		},
 		Series: series,
 	}
+	if len(markers) > 0 {
+		graph.Background.Padding.Bottom = 0 // compensate transparent tick space
+		graph.XAxis = chart.XAxis{
+			Style: chart.StyleShow(),
+			TickStyle: chart.Style{
+				StrokeColor: chart.ColorTransparent,
+			},
+			TickPosition: 10, // hide text with non-existing position
+			GridMajorStyle: chart.Style{
+				Show:            true,
+				StrokeColor:     chart.ColorAlternateGray,
+				StrokeWidth:     3.0,
+				StrokeDashArray: []float64{5.0, 5.0},
+			},
+			GridLines: markers,
+		}
+	}
 	graph.Elements = []chart.Renderable{
 		chart.Legend(&graph, chart.Style{
 			FillColor:   drawing.Color{A: 100},