Implement TakeElementScreenshot WebDriver command

components/compositing/compositor.rs

@@ -14,7 +14,7 @@ use crate::CompositionPipeline;
 use crate::SendableFrameTree;
 use crossbeam_channel::Sender;
 use embedder_traits::Cursor;
-use euclid::{Point2D, Scale, Vector2D};
+use euclid::{Point2D, Rect, Scale, Vector2D};
 use gfx_traits::Epoch;
 #[cfg(feature = "gl")]
 use image::{DynamicImage, ImageFormat};
@@ -442,8 +442,8 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
                 self.touch_handler.on_event_processed(result);
             },
 
-            (Msg::CreatePng(reply), ShutdownState::NotShuttingDown) => {
-                let res = self.composite_specific_target(CompositeTarget::WindowAndPng);
+            (Msg::CreatePng(rect, reply), ShutdownState::NotShuttingDown) => {
+                let res = self.composite_specific_target(CompositeTarget::WindowAndPng, rect);
                 if let Err(ref e) = res {
                     info!("Error retrieving PNG: {:?}", e);
                 }
@@ -1229,7 +1229,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
 
     pub fn composite(&mut self) {
         let target = self.composite_target;
-        match self.composite_specific_target(target) {
+        match self.composite_specific_target(target, None) {
             Ok(_) => {
                 if self.output_file.is_some() || self.exit_after_load {
                     println!("Shutting down the Constellation after generating an output file or exit flag specified");
@@ -1256,6 +1256,7 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
     fn composite_specific_target(
         &mut self,
         target: CompositeTarget,
+        rect: Option<Rect<f32, CSSPixel>>,
     ) -> Result<Option<Image>, UnableToComposite> {
         let size = self.embedder_coordinates.framebuffer.to_u32();
 
@@ -1347,6 +1348,22 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
             }
         }
 
+        let (x, y, width, height) = match rect {
+            Some(rect) => {
+                let rect = self.device_pixels_per_page_px().transform_rect(&rect);
+
+                let x = rect.origin.x as i32;
+                // We need to convert to the bottom-left origin coordinate
+                // system used by OpenGL
+                let y = (size.height as f32 - rect.origin.y - rect.size.height) as i32;
+                let w = rect.size.width as u32;
+                let h = rect.size.height as u32;
+
+                (x, y, w, h)
+            },
+            None => (0, 0, size.width, size.height),
+        };
+
         let rv = match target {
             CompositeTarget::Window => None,
             #[cfg(feature = "gl")]
@@ -1354,8 +1371,10 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
                 let img = gl::draw_img(
                     &*self.window.gl(),
                     rt_info,
-                    FramebufferUintLength::new(size.width),
-                    FramebufferUintLength::new(size.height),
+                    x,
+                    y,
+                    FramebufferUintLength::new(width),
+                    FramebufferUintLength::new(height),
                 );
                 Some(Image {
                     width: img.width(),
@@ -1378,8 +1397,10 @@ impl<Window: WindowMethods + ?Sized> IOCompositor<Window> {
                                 let img = gl::draw_img(
                                     gl,
                                     rt_info,
-                                    FramebufferUintLength::new(size.width),
-                                    FramebufferUintLength::new(size.height),
+                                    x,
+                                    y,
+                                    FramebufferUintLength::new(width),
+                                    FramebufferUintLength::new(height),
                                 );
                                 let dynamic_image = DynamicImage::ImageRgb8(img);
                                 if let Err(e) = dynamic_image.write_to(&mut file, ImageFormat::PNG)

components/compositing/compositor_thread.rs

@@ -8,6 +8,7 @@ use crate::compositor::CompositingReason;
 use crate::SendableFrameTree;
 use crossbeam_channel::{Receiver, Sender};
 use embedder_traits::EventLoopWaker;
+use euclid::Rect;
 use gfx_traits::Epoch;
 use ipc_channel::ipc::IpcSender;
 use msg::constellation_msg::{PipelineId, TopLevelBrowsingContextId};
@@ -17,6 +18,7 @@ use profile_traits::time;
 use script_traits::{AnimationState, ConstellationMsg, EventResult, MouseButton, MouseEventType};
 use std::fmt::{Debug, Error, Formatter};
 use style_traits::viewport::ViewportConstraints;
+use style_traits::CSSPixel;
 use webrender_api;
 use webrender_api::units::{DeviceIntPoint, DeviceIntSize};
 use webvr_traits::WebVRMainThreadHeartbeat;
@@ -80,7 +82,7 @@ pub enum Msg {
     /// Script has handled a touch event, and either prevented or allowed default actions.
     TouchEventProcessed(EventResult),
     /// Composite to a PNG file and return the Image over a passed channel.
-    CreatePng(IpcSender<Option<Image>>),
+    CreatePng(Option<Rect<f32, CSSPixel>>, IpcSender<Option<Image>>),
     /// Alerts the compositor that the viewport has been constrained in some manner
     ViewportConstrained(PipelineId, ViewportConstraints),
     /// A reply to the compositor asking if the output image is stable.

components/compositing/gl.rs

@@ -82,6 +82,8 @@ pub fn initialize_png(
 pub fn draw_img(
     gl: &dyn gl::Gl,
     render_target_info: RenderTargetInfo,
+    x: i32,
+    y: i32,
     width: FramebufferUintLength,
     height: FramebufferUintLength,
 ) -> RgbImage {
@@ -96,8 +98,8 @@ pub fn draw_img(
     gl.bind_vertex_array(0);
 
     let mut pixels = gl.read_pixels(
-        0,
-        0,
+        x,
+        y,
         width as gl::GLsizei,
         height as gl::GLsizei,
         gl::RGB,