c# - 裁剪图像时出现 OutofMemory 错误

Question

下面是我正在尝试的代码，但出现内存不足异常。

我正在尝试从通过 selenium 拍摄的屏幕截图中仅裁剪一个元素的图像。

            byte[] image= driver.GetScreenshot().AsByteArray;
                using (MemoryStream sourceStream = new MemoryStream(image))
                {
                    using (Bitmap source = new Bitmap(sourceStream))
                    {

                        Rectangle cropzone = new Rectangle(element.Location.X, element.Location.Y, element.Size.Width, element.Size.Height);
                        using (Bitmap croppedBitmap = source.Clone(cropzone, source.PixelFormat))
                        {
                            croppedBitmap.Save(file_name, System.Drawing.Imaging.ImageFormat.Png);
                        }
                    }
                }

Answer 1

当裁剪矩形位于屏幕截图之外时，会引发内存不足异常。如果屏幕截图包含整个页面，则需要使用相对于页面的位置来裁剪元素。如果没有，则需要将目标元素滚动到 View 中并使用相对于 View 的位置进行裁剪。

这是一个用于截取 WebElement 屏幕截图的扩展方法:

static class WebElementExt {

    public static Bitmap TakeScreenshot(this OpenQA.Selenium.IWebElement element) {
        RemoteWebDriver driver = (RemoteWebDriver)((RemoteWebElement)element).WrappedDriver;

        if (((IHasCapabilities)driver).Capabilities.HasCapability("takesElementScreenshot")) {

            byte[] bytes = ((RemoteWebElement)element).GetScreenshot().AsByteArray;
            return (Bitmap)Bitmap.FromStream(new MemoryStream(bytes, 0, bytes.Length, false, true), false, false);

        } else {
            var dict = (Dictionary<String, Object>)driver.ExecuteScript(@"
                arguments[0].scrollIntoView(true);
                var r = arguments[0].getBoundingClientRect(), scrollX = 0, scrollY = 0;
                for(var e = arguments[0]; e; e=e.parentNode) {
                  scrollX += e.scrollLeft || 0;
                  scrollY += e.scrollTop || 0;
                }
                return {left: r.left|0, top: r.top|0, width: r.width|0, height: r.height|0
                       , scrollX: scrollX, scrollY: scrollY, innerHeight: window.innerHeight}; "
                , element);

            var rect = new System.Drawing.Rectangle(
                Convert.ToInt32(dict["left"]),
                Convert.ToInt32(dict["top"]),
                Convert.ToInt32(dict["width"]),
                Convert.ToInt32(dict["height"]));

            byte[] bytes = driver.GetScreenshot().AsByteArray;
            using (Bitmap bitmap = (Bitmap)Bitmap.FromStream(new MemoryStream(bytes, 0, bytes.Length, false, true), false, false)) {

                if (bitmap.Height > Convert.ToInt32(dict["innerHeight"]))
                    rect.Offset(Convert.ToInt32(dict["scrollX"]), Convert.ToInt32(dict["scrollY"]));

                rect.Intersect(new System.Drawing.Rectangle(0, 0, bitmap.Width, bitmap.Height));
                if (rect.Height == 0 || rect.Width == 0)
                    throw new WebDriverException("WebElement is outside of the screenshot.");

                return bitmap.Clone(rect, bitmap.PixelFormat);
            }
        }
    }
}

还有一个使用示例:

var driver = new FirefoxDriver();
driver.Navigate().GoToUrl("http://stackoverflow.com");

driver.FindElementById("svnrev")
      .TakeScreenshot()
      .Save(@"screenshot-element.png", ImageFormat.Png);

driver.Quit();