automated snapshot

internal/ora/ora_support.go

@@ -0,0 +1,98 @@
+package ora
+
+import (
+	"archive/zip"
+	"encoding/xml"
+	"os"
+)
+
+type ORALayer struct {
+	Name     string
+	Filename string // relative to data/
+	Visible  bool
+	Opacity  float32 // 0..1
+	Blend    string  // svg:src-over, svg:multiply, etc
+}
+
+type imageXML struct {
+	XMLName xml.Name `xml:"image"`
+	W       int      `xml:"w,attr"`
+	H       int      `xml:"h,attr"`
+	Stack   stackXML `xml:"stack"`
+}
+
+type stackXML struct {
+	Layers []layerXML `xml:"layer"`
+}
+
+type layerXML struct {
+	Name       string  `xml:"name,attr"`
+	Src        string  `xml:"src,attr"`
+	Opacity    float32 `xml:"opacity,attr"`
+	Visible    bool    `xml:"visible,attr"`
+	Composite  string  `xml:"composite-op,attr"`
+}
+
+func WriteORA(
+	outPath string,
+	width, height int,
+	layers []ORALayer,
+	pngLoader func(name string) ([]byte, error),
+) error {
+
+	f, err := os.Create(outPath)
+	if err != nil {
+		return err
+	}
+	defer f.Close()
+
+	zw := zip.NewWriter(f)
+	defer zw.Close()
+
+	// 1. mimetype (must be first, uncompressed)
+	h := &zip.FileHeader{
+		Name:   "mimetype",
+		Method: zip.Store,
+	}
+	w, _ := zw.CreateHeader(h)
+	w.Write([]byte("image/openraster"))
+
+	// 2. stack.xml
+	var stack []layerXML
+	for _, l := range layers {
+		stack = append(stack, layerXML{
+			Name:      l.Name,
+			Src:       "data/" + l.Filename,
+			Opacity:   l.Opacity,
+			Visible:   l.Visible,
+			Composite: l.Blend,
+		})
+	}
+
+	img := imageXML{
+		W: width,
+		H: height,
+		Stack: stackXML{
+			Layers: stack,
+		},
+	}
+
+	xmlBytes, _ := xml.MarshalIndent(img, "", "  ")
+	xmlBuf := append([]byte(xml.Header), xmlBytes...)
+
+	w, _ = zw.Create("stack.xml")
+	w.Write(xmlBuf)
+
+	// 3. layer PNGs
+	for _, l := range layers {
+		data, err := pngLoader(l.Filename)
+		if err != nil {
+			return err
+		}
+		w, _ = zw.Create("data/" + l.Filename)
+		w.Write(data)
+	}
+
+	return nil
+}
+