From 127f3966d72cbab1b3bf36db065363becd37655f Mon Sep 17 00:00:00 2001
From: Pavel Feldman <pfeldman@chromium.org>
Date: Thu, 17 Aug 2017 21:11:39 -0700
Subject: [PATCH] Allow capturing transparent screenshots (#354)

This patch adds `omitBackground` option to the `page.screenshot` method.

Fixes #344
---
 docs/api.md                 |   1 +
 lib/Page.js                 |   4 ++++
 test/golden/transparent.png | Bin 0 -> 119 bytes
 test/test.js                |   6 ++++++
 4 files changed, 11 insertions(+)
 create mode 100644 test/golden/transparent.png

diff --git a/docs/api.md b/docs/api.md
index ccb2e82d3c8..917767bd504 100644
--- a/docs/api.md
+++ b/docs/api.md
@@ -604,6 +604,7 @@ Shortcut for [`keyboard.down`](#keyboarddownkey-options) and [`keyboard.up`](#ke
         - `y` <[number]> y-coordinate of top-left corner of clip area
         - `width` <[number]> width of clipping area
         - `height` <[number]> height of clipping area
+    - `omitBackground` <[boolean]> Hides default white background and allows capturing screenshots with transparency. Defaults to `false`.
 - returns: <[Promise]<[Buffer]>> Promise which resolves to buffer with captured screenshot
 
 #### page.setContent(html)
diff --git a/lib/Page.js b/lib/Page.js
index d9e6230b22e..ae33ac8324e 100644
--- a/lib/Page.js
+++ b/lib/Page.js
@@ -467,7 +467,11 @@ class Page extends EventEmitter {
       await this._client.send('Emulation.setDeviceMetricsOverride', { mobile, width, height, deviceScaleFactor, screenOrientation });
     }
 
+    if (options.omitBackground)
+      await this._client.send('Emulation.setDefaultBackgroundColorOverride', { color: { r: 0, g: 0, b: 0, a: 0 } });
     let result = await this._client.send('Page.captureScreenshot', { format, quality: options.quality, clip });
+    if (options.omitBackground)
+      await this._client.send('Emulation.setDefaultBackgroundColorOverride');
 
     if (options.fullPage)
       await this.setViewport(this._viewport);
diff --git a/test/golden/transparent.png b/test/golden/transparent.png
new file mode 100644
index 0000000000000000000000000000000000000000..1cf45d8688fc68c85c4d250d14eaf6fdf153ec82
GIT binary patch
literal 119
zcmeAS@N?(olHy`uVBq!ia0vp^DIm<j1|$m}O$`B3cAhSdAr*7p9yDYG@(wNd>YvN4
fzW~T20yHdVoU??1aarlqK9FipS3j3^P6<r_4B8dR

literal 0
HcmV?d00001

diff --git a/test/test.js b/test/test.js
index d1866568acc..577aa70de9d 100644
--- a/test/test.js
+++ b/test/test.js
@@ -1810,6 +1810,12 @@ describe('Page', function() {
         expect(screenshots[i]).toBeGolden(`grid-cell-${i}.png`);
       await Promise.all(pages.map(page => page.close()));
     }));
+    it('should allow transparency', SX(async function() {
+      await page.setViewport({ width: 100, height: 100 });
+      await page.goto(EMPTY_PAGE);
+      let screenshot = await page.screenshot({omitBackground:true});
+      expect(screenshot).toBeGolden('transparent.png');
+    }));
   });
 
   describe('Tracing', function() {