Added radius option & tidied up args with minimist

This adds a `--radius=<n>` option to control the animation radius from the CLI.

Also updates the README accordingly, puts the greyscaling into its own function, and adds some TODOs for things I was thinking of doing next.

README.md

@@ -1,19 +1,24 @@
 # party-party-party
-Turn a source image into an animated party emoji
+Turn a source image into an animated party emoji!
 
 This smiling emoji is pretty cool:
 
-![Smiling Emoji](https://raw.githubusercontent.com/scotchfield/party-party-party/master/smile.png "Smiling Emoji")
+![Smiling Emoji](./smile.png "Smiling Emoji")
 
 However, it might be jealous of all those parrots and their parties. Let's help out our emoji friend.
 
-![Party Smiling Emoji](https://raw.githubusercontent.com/scotchfield/party-party-party/master/party-smile.gif "Party Smiling Emoji")
+![Party Smiling Emoji](./party-smile.gif "Party Smiling Emoji")
 
-If you'd like to create emojis for Slack, make sure your input image is 128x128 (or less). If you want to tune the radius of the animating circle, you can change the following line: (larger values indicate more distance from the origin, i.e. a wider circle)
+## Usage
+`node index.js smile.png party.gif`
 
-`const partyRadius = 10;`
+Note: If you'd like to create emojis for Slack, make sure your input image is 128x128 (or less).
 
-![Party Heart Emoji](https://raw.githubusercontent.com/scotchfield/party-party-party/master/heart.gif "Party Heart Emoji")
+### Radius
+If you want to tune the radius of the animating circle, you can use the `--radius=<n>` option. The default for this is `10`.
 
-## Usage
-`node index.js smile.png party.gif`
+For example, `node index.js --radius=0 smile.png party.gif` will create a party version of `smile.png` where the image has an ounce or two less party.
+
+![Still Party Smile Emoji](./still-party-smile.gif "Still Party Smile Emoji")
+
+![Party Heart Emoji](./heart.gif "Party Heart Emoji")

index.js

@@ -1,14 +1,33 @@
 const fs = require("fs");
+const minimist = require("minimist");
 const getPixels = require("get-pixels");
 const gifEncoder = require("gif-encoder");
 
-if (process.argv.length <= 3) {
+// Process the arguments we're launched with and get rid of anything we won't be using.
+args = minimist(process.argv, {
+    default: {
+        "radius": 10, // 0 = regular stationary party
+    },
+    unknown: arg => {
+        // Filter out node and our index.js.
+        // This ensures that the args._ array will just be the files we process
+        if (arg === process.execPath) return false;
+        if (arg === __filename) return false;
+        return true;
+    }
+});
+
+//TODO(somewhatabstract): Make this code an importable module and then provide a simple wrapper for direct CLI usage
+//TODO(somewhatabstract): Consider adding some scaling or a --fitslack option?
+//TODO(somewhatabstract): Add ability to specify lots of different files at once.
+//TODO(somewhatabstract): Add error checks and useful help text.
+if (args._.length !== 2) {
     console.log("Usage: " + __filename + " input.png output.gif");
     process.exit(-1);
 }
 
-const inputFilename = process.argv[2];
-const outputFilename = process.argv[3];
+const inputFilename = args._[0];
+const outputFilename = args._[1];
 
 // The party palette. Party on, Sirocco!
 const colours = [
@@ -24,8 +43,9 @@ const colours = [
     [255, 105, 104]
 ];
 
+//TODO(somewhatabstract): Add other variations to radius, like tilt (for bobbling side to side)
 const partyOffset = [];
-const partyRadius = 10;
+const partyRadius = parseInt(args.radius);
 colours.forEach((c, colourIndex) => {
     const x =
         partyRadius * Math.sin(2 * Math.PI * (-colourIndex / colours.length));
@@ -34,14 +54,7 @@ colours.forEach((c, colourIndex) => {
     partyOffset.push([Math.round(x), Math.round(y)]);
 });
 
-function imageData(err, pixels) {
-    if (err) {
-        console.log("Invalid image path..");
-        console.log(err);
-        return;
-    }
-
-    const { shape } = pixels;
+function toGreyscale(pixels) {
     const greyscale = [];
 
     for (var i = 0; i < pixels.data.length / 4; i += 1) {
@@ -57,6 +70,18 @@ function imageData(err, pixels) {
             greyscale.push(avg);
         }
     }
+    return greyscale;
+}
+
+function imageData(err, pixels) {
+    if (err) {
+        console.log("Invalid image path..");
+        console.log(err);
+        return;
+    }
+
+    const { shape } = pixels;
+    const greyscale = toGreyscale(pixels);
 
     const gif = new gifEncoder(shape[0], shape[1]);
     const outputFile = fs.createWriteStream(outputFilename);