add functions to export page or svg to pdf and png formats

chrome.go

@@ -438,6 +438,61 @@ func (c *chrome) bounds() (Bounds, error) {
 	return bounds.Bounds, err
 }
 
+func (c *chrome) pdf(width, height int) ([]byte, error) {
+	result, err := c.send("Page.printToPDF", h{
+		"paperWidth":  float32(width) / 96,
+		"paperHeight": float32(height) / 96,
+	})
+	if err != nil {
+		return nil, err
+	}
+	pdf := struct {
+		Data []byte `json:"data"`
+	}{}
+	err = json.Unmarshal(result, &pdf)
+	return pdf.Data, err
+}
+
+func (c *chrome) png(x, y, width, height int, bg uint32, scale float32) ([]byte, error) {
+	if x == 0 && y == 0 && width == 0 && height == 0 {
+		// By default either use SVG size if it's an SVG, or use A4 page size
+		bounds, err := c.eval(`document.rootElement ? [document.rootElement.x.baseVal.value, document.rootElement.y.baseVal.value, document.rootElement.width.baseVal.value, document.rootElement.height.baseVal.value] : [0,0,816,1056]`)
+		if err != nil {
+			return nil, err
+		}
+		rect := make([]int, 4)
+		if err := json.Unmarshal(bounds, &rect); err != nil {
+			return nil, err
+		}
+		x, y, width, height = rect[0], rect[1], rect[2], rect[3]
+	}
+
+	_, err := c.send("Emulation.setDefaultBackgroundColorOverride", h{
+		"color": h{
+			"r": (bg >> 16) & 0xff,
+			"g": (bg >> 8) & 0xff,
+			"b": bg & 0xff,
+			"a": (bg >> 24) & 0xff,
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+	result, err := c.send("Page.captureScreenshot", h{
+		"clip": h{
+			"x": x, "y": y, "width": width, "height": height, "scale": scale,
+		},
+	})
+	if err != nil {
+		return nil, err
+	}
+	pdf := struct {
+		Data []byte `json:"data"`
+	}{}
+	err = json.Unmarshal(result, &pdf)
+	return pdf.Data, err
+}
+
 func (c *chrome) kill() error {
 	if c.ws != nil {
 		if err := c.ws.Close(); err != nil {

export.go

@@ -0,0 +1,56 @@
+package lorca
+
+import (
+	"fmt"
+	"io/ioutil"
+	"os"
+)
+
+const (
+	// PageA4Width is a width of an A4 page in pixels at 96dpi
+	PageA4Width = 816
+	// PageA4Height is a height of an A4 page in pixels at 96dpi
+	PageA4Height = 1056
+)
+
+// PDF converts a given URL (may be a local file) to a PDF file. Script is
+// evaluated before the page is printed to PDF, you may modify the contents of
+// the page there of wait until the page is fully rendered. Width and height
+// are page bounds in pixels. PDF by default uses 96dpi density. For A4 page
+// you may use PageA4Width and PageA4Height constants.
+func PDF(url, script string, width, height int) ([]byte, error) {
+	return doHeadless(url, func(c *chrome) ([]byte, error) {
+		c.eval(script)
+		return c.pdf(width, height)
+	})
+}
+
+// PNG converts a given URL (may be a local file) to a PNG image. Script is
+// evaluated before the "screenshot" is taken, so you can modify the contents
+// of a URL there. Image bounds are provides in pixels. Background is in ARGB
+// format, the default value of zero keeps the background transparent. Scale
+// allows zooming the page in and out.
+//
+// This function is most convenient to convert SVG to PNG of different sizes,
+// for example when preparing Lorca app icons.
+func PNG(url, script string, x, y, width, height int, bg uint32, scale float32) ([]byte, error) {
+	return doHeadless(url, func(c *chrome) ([]byte, error) {
+		c.eval(script)
+		return c.png(x, y, width, height, bg, scale)
+	})
+}
+
+func doHeadless(url string, f func(c *chrome) ([]byte, error)) ([]byte, error) {
+	dir, err := ioutil.TempDir("", "lorca")
+	if err != nil {
+		return nil, err
+	}
+	defer os.RemoveAll(dir)
+	args := append(defaultChromeArgs, fmt.Sprintf("--user-data-dir=%s", dir), "--remote-debugging-port=0", "--headless", url)
+	chrome, err := newChromeWithArgs(ChromeExecutable(), args...)
+	if err != nil {
+		return nil, err
+	}
+	defer chrome.kill()
+	return f(chrome)
+}