Example: Render static images using Orca (#7)

Author: MetalBlueberry

examples/static_image/README.md

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+# Static Image
+
+To save Plotly images as static images, you should use the [orca](https://github.com/plotly/orca) project. This example uses a docker image with orca to render a plot to PNG. You can refer to orca documentation to extend this further.

examples/static_image/main.go

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+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"strings"
+
+	grob "github.com/MetalBlueberry/go-plotly/graph_objects"
+)
+
+func main() {
+	/*
+	   fig = dict({
+	       "data": [{"type": "bar",
+	                 "x": [1, 2, 3],
+	                 "y": [1, 3, 2]}],
+	       "layout": {"title": {"text": "A Figure Specified By Python Dictionary"}}
+	   })
+	*/
+	fig := &grob.Fig{
+		Data: grob.Traces{
+			&grob.Bar{
+				Type: grob.TraceTypeBar,
+				X:    []float64{1, 2, 3},
+				Y:    []float64{1, 2, 3},
+			},
+		},
+		Layout: &grob.Layout{
+			Title: &grob.LayoutTitle{
+				Text: "A Figure Specified By Go Struct",
+			},
+		},
+	}
+
+	fmt.Fprint(os.Stderr, "saving to PNG...\n")
+	err := savePNG(fig, "out.png")
+	if err != nil {
+		panic(err)
+	}
+	fmt.Fprint(os.Stderr, "Done!\n")
+}
+
+func savePNG(fig *grob.Fig, path string) error {
+	args := "run --rm -i quay.io/plotly/orca graph --format png"
+	cmd := exec.Command("docker", strings.Split(args, " ")...)
+
+	in, err := cmd.StdinPipe()
+	if err != nil {
+		return fmt.Errorf("Failed to open StdIn, %w", err)
+	}
+	go func() {
+		err := json.NewEncoder(in).Encode(fig)
+		if err != nil {
+			panic(err)
+		}
+		err = in.Close()
+	}()
+
+	out, err := cmd.StdoutPipe()
+	if err != nil {
+		return fmt.Errorf("Failed to open StdOut, %w", err)
+	}
+
+	f, err := os.Create(path)
+	if err != nil {
+		return fmt.Errorf("Cannot create output file")
+	}
+	go func() {
+		defer f.Close()
+		_, err = io.Copy(f, out)
+		if err != nil {
+			panic(err)
+		}
+	}()
+
+	cmd.Stderr = os.Stderr
+
+	err = cmd.Run()
+	if err != nil {
+		return fmt.Errorf("Failed to run command, %w", err)
+	}
+
+	return nil
+}