make diff optional in cli; clean up

bin/pixelmatch

@@ -3,45 +3,52 @@
 
 'use strict';
 
-var PNG = require('pngjs').PNG,
-    fs = require('fs'),
-    match = require('../.');
+var PNG = require('pngjs').PNG;
+var fs = require('fs');
+var match = require('../.');
 
-if (process.argv.length < 5) {
-    console.log('Usage: pixelmatch image1.png image2.png output.png [threshold=0.005] [includeAA=false]');
+if (process.argv.length < 4) {
+    console.log('Usage: imagematch image1.png image2.png [diff.png] [threshold=0.005] [includeAA=false]');
     process.exit(64);
 }
 
-var threshold = isNaN(+process.argv[5]) ? undefined : +process.argv[5],
-    includeAA = process.argv[6] === 'true';
+var diffPath = process.argv[4];
+var threshold = isNaN(+process.argv[5]) ? undefined : +process.argv[5];
+var includeAA = process.argv[6] === 'true';
 
 var img1 = fs.createReadStream(process.argv[2]).pipe(new PNG()).on('parsed', doneReading);
 var img2 = fs.createReadStream(process.argv[3]).pipe(new PNG()).on('parsed', doneReading);
 
 function doneReading() {
     if (!img1.data || !img2.data) return;
 
-    if (img1.width !== img2.width || img1.height !== img2.height) {
-        console.log('Image dimensions do not match: %dx%d vs %dx%d',
-            img1.width, img1.height, img2.width, img2.height);
+    var width = img1.width;
+    var height = img1.height;
+
+    if (img2.width !== width || img2.height !== height) {
+        console.log('Image dimensions do not match: %dx%d vs %dx%d', width, height, img2.width, img2.height);
         process.exit(65);
     }
 
-    var diff = new PNG({width: img1.width, height: img1.height});
+    var diff = diffPath ? new PNG({width: width, height: height}) : null;
 
-    console.time('match');
-    var diffs = match(img1.data, img2.data, diff.data, diff.width, diff.height, {
+    console.time('matched in');
+    var diffs = match(img1.data, img2.data, diff ? diff.data : null, width, height, {
         threshold: threshold,
         includeAA: includeAA
     });
-    console.timeEnd('match');
-
-    var writeStream = diff.pack().pipe(fs.createWriteStream(process.argv[4]));
+    console.timeEnd('matched in');
 
     console.log('different pixels: ' + diffs);
-    console.log('error: ' + (Math.round(100 * 100 * diffs / (diff.width * diff.height)) / 100) + '%');
+    console.log('error: ' + (Math.round(100 * 100 * diffs / (width * height)) / 100) + '%');
 
-    writeStream.on('close', function () {
-        process.exit(diffs ? 66 : 0);
-    });
+    var exitCode = diffs ? 66 : 0;
+
+    if (diff) {
+        diff.pack().pipe(fs.createWriteStream(diffPath)).on('close', function () {
+            process.exit(exitCode);
+        });
+    } else {
+        process.exit(exitCode);
+    }
 }