Refactor save_output_image into own file so it can be reused in

servoshell and other embedders and let OHOS accept -x and -o flag.

Signed-off-by: Narfinger <Narfinger@users.noreply.github.com>

ports/servoshell/output_image.rs

@@ -0,0 +1,39 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
+
+use std::rc::Rc;
+
+use euclid::Point2D;
+use image::{DynamicImage, ImageFormat};
+use log::error;
+use servo::RenderingContext;
+use servo::webrender_api::units::DeviceIntRect;
+
+use crate::prefs::ServoShellPreferences;
+
+// This needs to be done before presenting(), because `ReneringContext::read_to_image` reads
+// from the back buffer.
+pub(crate) fn save_output_image_if_necessary<T>(
+    prefs: &ServoShellPreferences,
+    rendering_context: &Rc<T>,
+) where
+    T: RenderingContext + ?Sized,
+{
+    let Some(output_path) = prefs.output_image_path.as_ref() else {
+        return;
+    };
+
+    let size = rendering_context.size2d().to_i32();
+    let viewport_rect = DeviceIntRect::from_origin_and_size(Point2D::origin(), size);
+    let Some(image) = rendering_context.read_to_image(viewport_rect) else {
+        error!("Failed to read output image.");
+        return;
+    };
+
+    let image_format = ImageFormat::from_path(output_path).unwrap_or(ImageFormat::Png);
+    if let Err(error) = DynamicImage::ImageRgba8(image).save_with_format(output_path, image_format)
+    {
+        error!("Failed to save {output_path}: {error}.");
+    }
+}