Allow the output path to be specified for the `wrench png` subtool

wrench/src/args.yaml

@@ -85,6 +85,10 @@ subcommands:
               help: The input YAML file
               required: true
               index: 1
+          - OUTPUT:
+              help: The output PNG file
+              required: false
+              index: 2
     - show:
         about: show frame(s) described by YAML, binary recording, or capture
         aliases: ['load', 'replay']

wrench/src/main.rs

@@ -497,7 +497,15 @@ fn main() {
             _ => panic!("Unknown surface argument value")
         };
         let reader = YamlFrameReader::new_from_args(subargs);
-        png::png(&mut wrench, surface, &mut window, reader, rx.unwrap());
+        let output_path = match subargs.value_of("OUTPUT") {
+            Some(path) => PathBuf::from(path),
+            None => {
+                let mut path = reader.yaml_path().clone();
+                path.set_extension("png");
+                path
+            }
+        };
+        png::png(&mut wrench, surface, &mut window, output_path, reader, rx.unwrap());
     } else if let Some(subargs) = args.subcommand_matches("reftest") {
         // Exit with an error code in order to ensure the CI job fails.
         process::exit(reftest(wrench, &mut window, subargs, rx.unwrap()) as _);

wrench/src/png.rs

@@ -6,7 +6,7 @@ use {WindowWrapper, NotifierEvent};
 use image::png::PNGEncoder;
 use image::{self, ColorType, GenericImage};
 use std::fs::File;
-use std::path::Path;
+use std::path::{Path, PathBuf};
 use std::sync::mpsc::Receiver;
 use webrender::api::*;
 use wrench::{Wrench, WrenchThing};
@@ -76,6 +76,7 @@ pub fn png(
     wrench: &mut Wrench,
     surface: ReadSurface,
     window: &mut WindowWrapper,
+    out_path: PathBuf,
     mut reader: YamlFrameReader,
     rx: Receiver<NotifierEvent>,
 ) {
@@ -106,8 +107,5 @@ pub fn png(
         }
     };
 
-    let mut out_path = reader.yaml_path().clone();
-    out_path.set_extension("png");
-
     save(out_path, data, device_size, settings);
 }