Add `png' command to save the result of a yaml file

wrench/src/args.yaml

@@ -52,6 +52,13 @@ args:
       help: Enable vsync for OpenGL window
 
 subcommands:
+    - png:
+        about: render frame described by YAML and save it to a png file
+        args:
+          - INPUT:
+              help: The input YAML file
+              required: true
+              index: 1
     - show:
         about: show frame(s) described by YAML
         args:

wrench/src/main.rs

@@ -30,6 +30,7 @@ extern crate yaml_rust;
 mod binary_frame_reader;
 mod json_frame_writer;
 mod parse_function;
+mod png;
 mod reftest;
 mod scene;
 mod wrench;
@@ -313,6 +314,10 @@ fn main() {
             Box::new(YamlFrameReader::new_from_args(subargs)) as Box<WrenchThing>
         } else if let Some(subargs) = args.subcommand_matches("replay") {
             Box::new(BinaryFrameReader::new_from_args(subargs)) as Box<WrenchThing>
+        } else if let Some(subargs) = args.subcommand_matches("png") {
+            let reader = YamlFrameReader::new_from_args(subargs);
+            png::png(&mut wrench, &mut window, reader);
+            return;
         } else if let Some(subargs) = args.subcommand_matches("reftest") {
             let harness = ReftestHarness::new(&mut wrench, &mut window);
             let base_manifest = Path::new("reftests/reftest.list");

wrench/src/png.rs

@@ -0,0 +1,62 @@
+/* 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 http://mozilla.org/MPL/2.0/. */
+
+use WindowWrapper;
+use gleam::gl;
+use image::ColorType;
+use image::png::PNGEncoder;
+use std::fs::File;
+use std::sync::mpsc::{channel, Sender};
+use webrender_traits::*;
+use wrench::{Wrench, WrenchThing};
+use yaml_frame_reader::YamlFrameReader;
+
+pub fn png(wrench: &mut Wrench,
+           window: &mut WindowWrapper,
+           mut reader: YamlFrameReader)
+{
+    // setup a notifier so we can wait for frames to be finished
+    struct Notifier {
+        tx: Sender<()>,
+    };
+    impl RenderNotifier for Notifier {
+        fn new_frame_ready(&mut self) {
+            self.tx.send(()).unwrap();
+        }
+        fn new_scroll_frame_ready(&mut self, _composite_needed: bool) {}
+    }
+    let (tx, rx) = channel();
+    wrench.renderer.set_render_notifier(Box::new(Notifier { tx: tx }));
+    reader.do_frame(wrench);
+
+    // wait for the frame
+    rx.recv().unwrap();
+    wrench.render();
+
+    let size = window.get_inner_size_pixels();
+    let mut data = gl::read_pixels(0,
+                                   0,
+                                   size.0 as gl::GLsizei,
+                                   size.1 as gl::GLsizei,
+                                   gl::RGBA,
+                                   gl::UNSIGNED_BYTE);
+    let width = size.0;
+    let height = size.1;
+
+    // flip image vertically (texture is upside down)
+    let orig_pixels = data.clone();
+    let stride = width as usize * 4;
+    for y in 0..height as usize {
+        let dst_start = y * stride;
+        let src_start = (height as usize - y - 1) * stride;
+        let src_slice = &orig_pixels[src_start .. src_start + stride];
+        (&mut data[dst_start .. dst_start + stride]).clone_from_slice(&src_slice[..stride]);
+    }
+
+    let encoder = PNGEncoder::new(File::create("out.png").unwrap());
+    encoder.encode(&data[..],
+                   width,
+                   height,
+                   ColorType::RGBA(8)).expect("Unable to encode PNG!");
+}