Monday, February 29, 2016

It's Leap Day

Today is Leap Day, which in my opinion is the froggiest of days. As such, the frogs in my webcomic are celebrating with an office party. I, however, am working like a normal person today.

This is my 10th leap day, but the first one since I've been writing the comic. The next one will come around in 2020 and by then I may have stopped writing the this might be the only chance the frogs will have to celebrate.

I've been thinking about Leap Days quite a bit this weekend, and I've decided that I don't care for them. The reason for having them is that the Earth actually completes a rotation around the sun in 365 days, 5 hours, 48 minutes, and 45 seconds. Those extra 5.8125 hours add up, so every 4 years we add 1 day. But really, 5.8125 x 4 = 23.25. By adding 24 hours when we really only need 23 hours and 15 minutes, we end up with an extra 45 minutes every 4 years and over the span of 32 leap years that adds up to a whole extra day. So on century marks that aren't divisible by 400 (such as 1700, 1800, and 1900) we don't add the leap day even though they are divisible by 4 and we're pretty much back on track. Except those numbers aren't quite exactly perfect and we'll still be off by a day every 3,300 years. It hasn't happened yet, but if humans are still around by the time it does, people are going to be really confused.

I would like to propose a simpler solution. We eliminate Daylight Savings Time and just add those 5.815 hours in throughout the year in the middle of the night. You go to bed some nights and you get just a little extra sleep because your clock adds on a few minutes for you. Like 2:00 AM sticks around for 5 minutes or so. No one will notice. Sure, your watch might be off "official time" the next day but you probably won't even notice. Who really notices 5 minutes? And since everyone has smart watches now, they'll adjust themselves right along with it and no one will be the wiser.

You only need a watch with 3 "times" on it anyway. Wake up. Eat. Go to sleep. All these hours and minutes and seconds are just not necessary. Let's keep things simple.

Think about that as you're leaping through your day. And here's the link to the comic... comic for 29 February 2016

Friday, February 26, 2016

"Loading" Screens in Phaser Games

I noticed an annoying thing when playing my Phaser platformer on - it was taking a really long time to start the levels. The problem was mainly that I was re-loading the game assets every time a level was started, and that I wasn't pre-loading them way back before the title screen.


I wanted to fix this issue and add a "Loading" screen at the beginning before the main stage select menu was available. The way to do this is to add a few more states to the game.

First, I added a boot state. All this state will do is load the title background image and an image that says "Loading." This happens in the preload function, and should go fairly quickly. In the create function for this state, which will be called as soon as preload completes, it will immediately start the next state - the real preloader. Check out the following code from the game (remember, the full source code is available on GitHub):

var boot = {
    preload: function() {"title", "assets/images/title.png");"title-loading", "assets/images/title-loading.png");
    create: function() {

The second state I added was called preloader. This will serve as the game's real preloader. I moved the asset pack loading from my other two existing states (the menu and the playable level) to the preload function of this state. But before I start loading assets, I display the two assets I loaded in the boot state's preload. I can use those assets here because they were loaded before this function - even though this is a preload function it's not the first one. Basically, you can use assets in preload as long as they've already been loaded by a previous state's preload. This will show the player the nice title screen and let them know that the game is loading. After all the assets are loaded, the create function is called for this state, which changes to the stageSelect state.

var preloader = {
    preload: function() {
        this.add.image(0, 0, "title");
        this.loadingText = this.add.image(450, 200, "title-loading");
        this.load.pack("main", "assets/pack.json");

    create: function() {

Now when I set up my game, I add all 4 states and then start the boot state.

var game = new Phaser.Game(width, height, Phaser.CANVAS, "gameArea");

game.state.add("boot", boot);
game.state.add("preloader", preloader);
game.state.add("stageSelect", stageSelectState);
game.state.add("level", theStage);


It still takes a while to load all the assets, but at least now you know what's going on. And once you make it to the menu, all the levels will start immediately for you. Much better. The process of loading assets still takes a while because the background music files are so large. I'll probably fix that by reducing their quality a little. Don't worry, you won't notice.

You might notice something wrong with today's comic, however... comic for 26 February 2016

Wednesday, February 24, 2016

Swimming in a Phaser Platformer

The theme for Level 7 of my 8-bit style Phaser platformer has been selected - Liquid Cooled! It's a water level with a name that also describes a high-performance computer needing more than just a normal CPU fan.

But a water level means the frog has to swim through it, instead of jump. I had to make a few changes to my code in order to support an optional "swim mode" behavior. I handled this by putting a water flag in my level objects. When true, it means the physics should be more...liquid.

The swimming level. All platformers should have at least one.

To start, the gravity needed to be adjusted. I have the normal gravity set to 1500 in my game, but I played around with different numbers and 250 seemed most appropriate for a swimming effect. In real life, gravity doesn't decrease when you're in water...but the effect of your body's buoyancy makes it seem as if it does. Same thing here.

function create() {

    // ... other stuff ...

    if (waterLevel) {
        this.physics.arcade.gravity.y = 250;
    } else {
        this.physics.arcade.gravity.y = 1500;

    // ... other stuff ...


The other thing that needed to change was the jump behavior. On land, the frog can't start a new jump while still in mid-air. But in the water, doing so gives the impression of swimming. Also, the amount of upward thrust supplied by a jump should be lessened under water. The speed at which the frog moves left and right should also be reduced.

function update() {

    // ... other stuff ...

    var xVel = waterLevel ? 100 : 150;
    var yVel = waterLevel ? -250 : -400;
    var jumpFrames = waterLevel ? 26 : 31;
    if (spacebar.isDown) {

        if ((frog.body.onFloor() || frog.locked || waterLevel) && jumpTimer === 0) {
            // jump is allowed to start
            jumpTimer = 1;
            frog.body.velocity.y = yVel;
        } else if (jumpTimer > 0 && jumpTimer < jumpFrames && !frog.body.blocked.up && !frog.body.touching.up) {
            // keep jumping higher
            frog.body.velocity.y = yVel + (jumpTimer * 7);
        } else if (frog.body.blocked.up || frog.body.touching.up) {
            // permanently end this jump
            jumpTimer = 999;

    } else {
        // jump button not being pressed, reset jump timer
        jumpTimer = 0;

    if (cursors.left.isDown) {
        frog.body.velocity.x = -xVel;
    } else if (cursors.right.isDown) {
        frog.body.velocity.x = xVel;

    // ... other stuff ...


Lines 5-7 in the code snippet above set the values for x-velocity, y-velocity, and length of a jump (in frames). These used to be hard-coded to the non-water values, but now there's a water option. In the check to see if a jump can start, line 11, I've added the condition that if this is a water level, jumps can start even if the frog is not on the ground or locked to a floating platform. The jump sets the y-velocity to the appropriate value, and the cursor keys set the x-velocity.

With these relatively simple adjustments in place, it really feels like the frog is swimming through Level 7. You can play it yourself on, and make sure you also check out today's comic while you're there! If you're more interested in the complete source code for the game, you can find that on GitHub. But seriously, read the comic. It's funny. Most of the time. comic for 24 February 2016

Monday, February 22, 2016

Setting Up Level Bosses with Phaser

I've reached the phase of my development on my Phaser platformer where I refactor everything. This weekend, it was the level bosses. If you looked at much earlier versions of the game or read my blog posts from a couple months ago, you might remember that I had one sandbox level with a dinosaur as the boss at the end. He was pretty much hard-coded in there, so adding different bosses for each level was difficult.

To make it better, I added a field to my level objects called boss. I assign a function to that field, which creates the boss Sprite. I can assign different "boss" functions to each level.

function beaver(game, group, frog) {
    // ... set up the boss beaver

function dinosaur(game, group, frog) {
    // ... set up the boss dinosaur

var levelOne = { // Vector Factory
        map: "Level1",
        music: "assets/audio/Ouroboros.mp3",
        background: "#141414",
        boss: beaver

var levelTwo = { // Binary Trees
        map: "Level2",
        music: "assets/audio/Club_Diver.mp3",
        background: "#000066",
        boss: dinosaur

// ... define other levels here ...

var gameState = {
        levels: [],
        currentLevel: -1,
        lives: 3

// populate the levels array (add more the same way)    
gameState.levels[0] = levelOne;
gameState.levels[1] = levelTwo;

In my game's create function, I call the boss function of whatever level is currently being played. I then add the kill behavior to the boss Sprite, which is to end the level and return to the stage select screen.

function create() {

    // ... other stuff ...

    // create a group for all the enemies
    enemies =;

    // create our hero sprite
    frog = createFrog();

    // --------------- set up the boss for this level
    var theBoss = gameState.levels[gameState.currentLevel].boss(this, enemies, frog); {
        // this level is complete! change state!
    }, this);

    // ... other stuff ...


Now it's fairly easy to add new bosses and even switch them around from one level to another. But you may wonder why I chose to always pass in those three parameters to the boss functions - game, group, and frog.

The first thing that the boss setup function must do is to create the boss Sprite, and to accomplish that I need the game object, the group in which to place this boss, and a reference to the frog object so the boss's behavior can change based on attributes such as the frog's proximity or other such things.

// function create the boss beaver
function beaver(game, group, frog) {

    // create this boss:
    //     150 pixels from the far right edge of the level,
    //     100 pixels from the top of the level,
    //     using the spritesheet with the key of "beaver"
    var obj = game.add.sprite( - 150, 100, "beaver", 0, group);

    // ... other stuff ...

    return obj;


If these little snippets of code aren't enough, you can see the game's complete source code on GitHub.

Try the game out for yourself at, and also be sure to read today's comic while you're there (or go right to the comic with the link below!). comic for 22 February 2016

Friday, February 19, 2016

My Level Design, So Far

With most of the game mechanics getting pretty solid in my platformer, I've been devoting more time to the level design. Here's what I have so far.

There are going to be 8 levels, one for each bit in a byte. I want each one to have at least some loose tie-in with a software engineering technology, much like how the Tron arcade game's difficulty levels were (mostly) named after programming languages. Those were RPG, COBOL, BASIC, FORTRAN, SNOBOL, PL1, PASCAL, ALGOL, ASSEMBLY, OS, JCL, and USER, if you've forgotten. I've programmed in 4 of them. I won't tell you which ones.

But anyway, here are my levels so far:

Level 1 - Vector Factory. Kind of a dark, industrial feel.

Level 2 - Binary Trees. It's a forest. Lots of trees. And pits.

Level 3 - Silicon Dioxide Valley. A desert. Sand and stuff.

Level 4 - Cloud Computing. Also some ice. In the sky.

Level 5 - Containers. There are lots of boxes. And a dock.

Level 6 - Deployment Pipeline. You guessed it - pipes.

I don't really have anything for 7 or 8 yet. Leave a comment below if you have any suggestions. Also, you can check out the game's complete source code on GitHub or play the current unfinished version on You can also view today's comic there as well! comic for 19 February 2016

Wednesday, February 17, 2016

Hitting the Wall - The Difference Between "blocked" and "touching" in Phaser

I've made another small improvement to my 8-bit style Phaser platformer. Now that I have some more complete levels in place, I noticed that if the frog was jumping and hit his head on the jump wasn't ending. He would just kind of hover there, in collision with the overhead tile, until the jump timer was up (I discussed my use of a timer to control the jump behavior previously).

I wanted to cancel the upward motion in the event of an overhead collision. Phaser has two ways of detecting this kind of thing in the Arcade physics engine: blocked and touching. The blocked and touching fields on the Sprite physics body are objects which each contain four boolean values - one for each direction. When true, these values indicate a collision on that side of the Sprite.

if (sprite.body.blocked.right) {
    // running into a wall on the right
} else if (sprite.body.blocked.left) {
    // running into a wall on the left
} else if (sprite.body.blocked.up) {
    // hitting something above
} else if (sprite.body.blocked.down) {
    // on the ground. same as sprite.body.onFloor() ??

if (sprite.body.touching.right) {
    // hitting another sprite on the right
} else if (sprite.body.touching.left) {
    // hitting another sprite on the left
} else if (sprite.body.touching.up) {
    // hitting another sprite above
} else if (sprite.body.touching.down) {
    // hitting another sprite below

So what's the difference? The blocked object refers to the Sprite colliding with a Tile. Since I am using a Tilemap for each level in my game, blocked will tell me if the frog is hitting some part of the environment. The touching object refers to the Sprite touching another sprite. I could use that field to determine if the frog hits an overhead enemy, for example.

For now, I've updated my jump control algorithm to take the Tile collision case into account.

function update() {

    // ... other stuff ...

    if (spacebar.isDown) {
        if ((frog.body.onFloor() || frog.locked) && jumpTimer === 0) {
            // jump is allowed to start
            jumpTimer = 1;
            frog.body.velocity.y = -400;
        } else if (jumpTimer > 0 && jumpTimer < 31 && !frog.body.blocked.up) {
            // keep jumping higher
            frog.body.velocity.y = -400 + (jumpTimer * 7);
        } else if (frog.body.blocked.up) {
            // permanently end this jump
            jumpTimer = 999;
    } else {
        // jump button not being pressed, reset jump timer
        jumpTimer = 0;

    // ... other stuff ...


The changes are minor, but important. If the player continues to hold down the spacebar, the jump will only keep going higher if the frog is not being blocked from above. If he is being blocked, I set the jumpTimer to a high value, to ensure that the jump is over - treated basically the same way that it would be if the player let go of the spacebar. If I don't do this, on the next frame the frog will have dropped a little bit and be out of collision, which will make the second branch of the nested if-else block true again and he'll move up some more. This causes the overhead collision to re-occur, and it's a viscous cycle until we get past 30 frames!

That's all I've changed for today, but that's actually good news. It means I'm much closer to being finished with the game, since I'm working on such small details. Maybe by the end of the month it will be complete. For now, you can view the source code on GitHub and play the game in its unfinished state here.

Be sure to read today's comic! It's about load balancers. Or see-saws. Or both. comic for 17 February 2016

Monday, February 15, 2016

Switching to Frame Based Tweens in Phaser

This weekend I was doing some more work on my 8-bit style Phaser platformer. I added another enemy (a rabbit) and made some changes which will make it easier to add even more enemies. But during my extensive play-testing I noticed that I was having a lot of trouble with my moving platforms. Both the ridable clouds and the collapsing platforms seemed to move away from the frog, and then the frog's motion became very choppy as it was repositioned.

Frogs can now battle rabbits in the dark forest.

After playing around with some things, I determined that the issue was caused by a slightly lagging frame rate. I had a bunch of other things running on my laptop and the game wasn't running quite as quickly as it was before. The physics engine, which controlled the frog's movements, was making updates based on how much time was elapsing between frames. The movement of the platforms was being handled by Tweens, which by default calculate their movement in constant time. When the frame rate dips below 60 per second, the two get out of sync. Normally this would not be that noticeable but in the situation where the two objects are tied together, it caused some issues.

To resolve these problems, I switched the Tweens into "frame based" mode. This is as easy as setting a boolean flag once in the create function.

function create() {
    // ... other stuff ...
    this.tweens.frameBased = true;

    // ... other stuff ...


When running in frame based mode, the Tweens will use the physics engine's update timer. When I switched to this mode, the frog and the platforms remain in sync much better when the frame rate dips a little. I did have to adjust the duration values in most of my Tweens, since in frame based mode the duration should represent number of frames instead of number of milliseconds. But it was a simple adjustment.

Remember, you can view the complete source code for the game on GitHub, and play the current version at this link:

Before you go, be sure to read today's comic - and give me a vote on if you have an extra second! comic for 15 February 2016

Friday, February 12, 2016

Happy Valentine's Day

I also love frogs.
With Valentine's Day only 2 days from now, I thought I'd take this opportunity to talk about love. What do I know about love? I know that the English language expresses it very poorly.

For example,

I love my wife.
I love my children.
I love pizza.

Those three sentences use the same word, but all refer to very different kinds of love. Why does our language have so little precision when it comes to such an important concept? I have no idea. I just use English; I didn't invent it.

Facebook is famous for its Like button, but it has no Love button. Twitter just replaced Favorite with Like, but Like is represented by a heart. On Facebook, Like is a thumbs-up. Does that mean Twitter likes are more passionate? Does anyone else besides me wonder about these things?

Today's comic has a special feature - there are two hidden frames at the end which will become visible once the comic has at least 50 likes on Facebook. In mathematical terms, 50 likes = 1 love. Who says I can't mix logic and emotion? Vulcans, I guess. comic for 12 February 2016

Wednesday, February 10, 2016

Don't Fall Through - "Tile Bias" in Phaser

Despite getting a lot of good level design accomplished this weekend, and adding collapsing platforms to my Phaser platformer, my free time since Sunday has been extremely limited. I haven't been able to work on much else, so today's post will be short.

One thing I would like to address is the use of "tile bias" in Phaser. In one of my levels, I had an issue where if the frog jumped from a platform near the top of the screen he would fall through the ground instead of colliding with it. It wouldn't happen 100% of the time, but it was often enough. I'd seen this type of problem before, back when I wrote my own HTML5 game engines instead of using Phaser. It is a classic problem - when there is too much time lapsing between frames (for whatever reason - slow computer, too many background tasks, etc.) the physics engine can miss collisions. A fast-moving sprite can traverse such a great distance in the time between frame updates that its bounding box ends up completely on the other side of an object with which it should have collided.

When it comes to a sprite colliding with a tilemap in Phaser, the collision calculation can be tuned by changing the value of TILE_BIAS. This was exactly what I needed to do because the issue was the frog hitting (or in this case, not hitting) a ground tile.

The default value for TILE_BIAS appears to be 16. This means that for a 32x32 tile, there's a 48x48 box when it comes to collision checks. It doesn't mean that a colliding sprite is moved back an extra 16 pixels to get it out of collision, the value is only used for the collision check. So don't worry - a sprite can still appear to be right next to a tile! I tried changing the value from 16 to 32 and that solved the problem for me. If you have a similar issue in your game, you'll probably have to play around with the number to find what works in your situation.

I change the value in my create function, at the same time I set up the other physics stuff.

function create() {
    game.physics.arcade.checkCollision.down = false;
    game.physics.arcade.TILE_BIAS = 32;
    game.physics.arcade.gravity.y = 1500;

    // ... other stuff ...


Remember, if you want to view the complete source code for the game it is available on GitHub. And remember to view today's comic. Both comics so far this week have dealt with lunch. Maybe I'm hungry when I'm writing these. comic for 10 February 2016

Monday, February 8, 2016

Collapsing Platforms in Phaser

I've been working on level design over the last few days for my Phaser platformer (view the complete source code on GitHub). I used my floating, ride-able cloud platforms (that I wrote about last week) in a few places, but I also found a few places where I wanted to use a collapsing platform. You know, one that falls after you stand on it for a little while.

The red-and-black platforms will fall after you jump on them.

To start, they are very similar to the riding platforms. The difference is in the custom collision callback function, shown below.

function fallPlatformSep(s, platform) {

    if (!s.locked) {

    if (!platform.activated) {

        platform.activated = true;

        // save the original Y-value
        var origY = platform.position.y;, function() {

            var t =;
            var dist = (( + 100) - platform.y);
            var time = dist * 2.25;
   { y: platform.position.y + dist }, time, Phaser.Easing.Quadratic.In, false, 0, 0, false);
            t.onComplete.add(function() {

                // after falling, wait 2 sec. before putting it back
      , function() {
                 platform.activated = false;
                 platform.position.y = origY;
                 var t2 =;
       { alpha: 0.5 }, 100, Phaser.Easing.Linear.None, true, 0, 3, true);



        }, this);

function update() {

    // ... other stuff ...

    this.physics.arcade.collide(frog, fallingPlatforms, fallPlatformSep, null, this);

    // ... other stuff ...


Since this function is called when the frog and the falling platform are colliding, the first step is to "activate" the platform, if it has not been activated already. This block should be entered the first time that the frog lands on the platform and won't be entered again no matter how long he stands on it.

The next step is to make a note of the original Y-value, so it can be put back a few seconds after it falls off the screen. The drop and restoration is handled by a few game timers and tweens. The first timer sets it up so that the platform will drop 1000 milliseconds after the first contact. Inside the timer function, I set up a Tween to move the platform down to a final position of 100 pixels below the world bounds. This makes sure that if the frog rides it to the bottom he will be complete off-world and trigger the kill function.

I'm using the Phaser.Easing.Quadratic.In easing function in the drop so that it gets off to a slow start. I actually found a very useful page with live demos of all the Phaser easing functions: just click here!

When the drop Tween completes, I set a second timer. Two seconds after the fall, the platform gets set back to its original Y-position and once again becomes inactive. Just to make it look nice, I use another Tween here to blink the alpha a few times.

But don't let your interest in my comics drop as fast as these platforms! Check out today's comic before you go to other parts of the Internet, or order lunch, or whatever. comic for 8 February 2016

Friday, February 5, 2016

Use Tiled's Custom Properties in Phaser

To make editing the maps for my Phaser platformer easier, I decided to make use of the custom properties Tiled lets you add to objects. These get directly translated to fields on the Sprite objects if you use the createFromObjects function to pull them from the map.

I used this technique on my moving cloud platforms. In the map editor, I select the object and then add two custom properties: direction and distance.

Adding two custom properties in Tiled

Once I saved my map, I could then use those properties when I set up my moving cloud platforms. In the create function, I make the platforms from the objects on the map. Look at the following code.

function create() {

    // ... other stuff ...

    platforms =;
    platforms.enableBody = true;
    map.createFromObjects('others', 6573, 'cloud-blue', 0, true, false, platforms);
    platforms.forEach(function(p) {
        this.physics.enable(p, Phaser.Physics.ARCADE);
        p.body.allowGravity = false;
        p.body.immovable = true;
        var t = this.add.tween(p.position);

        // use the distance and direction custom properties
        // to set up the Tween
        var dist = (p.distance ? Number(p.distance) : 128);
        if (p.direction == "left") {
   { x: p.position.x - dist }, 3000, Phaser.Easing.Linear.None, true, 0, -1, true);
        } else if (p.direction == "right") {
   { x: p.position.x + dist }, 3000, Phaser.Easing.Linear.None, true, 0, -1, true);
        } else if (p.direction == "up") {
   { y: p.position.y - dist }, 3000, Phaser.Easing.Linear.None, true, 0, -1, true);
        } else if (p.direction == "down") {
   { y: p.position.y + dist }, 3000, Phaser.Easing.Linear.None, true, 0, -1, true);
    }, this);

    // ... other stuff ...


As I iterate over them to perform their setup, I can read p.distance and p.direction in order to customize the movement Tween. I first check to see if distance is defined and use a default value if it is not. This way, the game doesn't fail if I forget to set the custom property. I then check the value of the direction field and set the Tween accordingly. If I forget to set direction on one of my objects, it just won't move because the to function will never be called on the Tween.

I like this method because it allows me to quickly and easily tweak the level in the map editor until I get the level design right. I don't have to go back to change any code when I want to move a platform's starting position, direction, or travel distance. I might add a third property set set the speed as well.

Remember, you can see the complete source code for the game on GitHub!

While you're here, why don't you take a few minutes and catch up on some comics that you may have missed - like today's! It deals with the first and best troubleshooting technique there is. comic for 5 February 2016

Wednesday, February 3, 2016

Ride Moving Platforms in a Phaser Game

Another staple of classic platformers that my Phaser game has been missing is the moving platform. You know, those floating platforms that go up and down or side to side and upon which you can ride? I had to add some. It wasn't that hard, but there were some tricks to it.

This is the frog's new cloud platform.

First, I had to add the sprites for the moving platforms. I did this by adding them to my map in Tiled as objects, the same way I added the enemies (see that blog post here).

platforms =;
platforms.enableBody = true;
map.createFromObjects('others', 6573, 'cloud-blue', 0, true, false, platforms);
platforms.forEach(function(p) {
    game.physics.enable(p, Phaser.Physics.ARCADE);
    p.body.allowGravity = false;
    p.body.immovable = true;
    var t = this.add.tween(p.position);{ y: p.position.y - 200 }, 3000, Phaser.Easing.Linear.None, true, 0, -1, true);
}, this);

Every object with id 6573 was assigned the "cloud-blue" sprite image key and put in the platforms group. Then I iterate over the group to set them all up with physics so they can collide with the frog. I turn off gravity on them so they don't fall off the screen, and I set body.immovable to true. This isn't to say that they can't move - it just means that they won't react to being pushed down when the frog lands on them. The movement of the platforms is controlled by Tweens. In the above code snippet, all of the platforms are given the same Tween. This one example Tween will move the platform up 200 pixels from its start position in 3 seconds and then loop forever. In my finished game I'll use different Tweens for different platforms.

After that, adding a collision check in the update function between the frog and the platforms group was all it took to make the platforms solid.

I now had moving platforms upon which the frog could land, but the behavior wasn't correct. As the platform moved up it would push the frog up with it, but on the way down the frog would keep falling and hitting the platform over and over again. It didn't look like he was riding it. The solution was to create a special collision callback function which "locks" the frog to the platform upon which he stands.

function platformSep(s, platform) {

    if (!s.locked) {
        s.locked = true;
        s.lockedTo = platform;
        s.body.velocity.y = 0;


function update() {

    this.physics.arcade.collide(frog, platforms, platformSep, null, this);

    // ... other stuff ...

    if (frog.locked) {
        if (frog.body.right < frog.lockedTo.body.x || frog.body.x > frog.lockedTo.body.right) {
            frog.locked = false;
            frog.lockedTo = null;
        } else {
            frog.x += frog.lockedTo.deltaX;
            frog.y += frog.lockedTo.deltaY;

    // ... other stuff ...


Now, when the frog and a platform are in collision, the frog will get a locked flag set to true, and the lockedTo field will be set to the platform sprite on which he stands. The frog's y-velocity is also set to 0 here to stop any potential falling that might occur otherwise.

Once I had these additional fields, I could perform a check to see if the frog is currently locked to a platform. If he is, but his current position says that he's walked off of it, I cancel the lock and his behavior goes back to normal. Otherwise, the frog's position gets updated to match the movement deltas of the platform. This keeps him riding it, no matter which in direction it moves.

These moving platforms really add a lot of classic platformer feel to the game, and thanks to Phaser they weren't too difficult to add. Remember, you can see the complete source code to the game on GitHub and play the current version at this link!

There are some major upgrades going on in the comic today, so don't forget to read it! comic for 3 February 2016

Monday, February 1, 2016

Generating Color Gradients with JavaScript

The comic frames with the color
gradient backgrounds.
For the comic on Friday, I had to generate a color gradient between the full-brightness daylight color in the third frame and the nighttime darkness color in the fourth frame. Since the point of the comic was to adjust the brightness using a slider with 20 positions, I needed 40 colors (including the 2 starting colors) so that when the brightness was all the way down both frames would have the same background. They would meet in the middle.

It was actually a very nice comic. On the right you can see the frames with the color gradients, but the real comic is interactive - go play around with it if you haven't yet!

To generate the gradient of colors, I found a set of JavaScript functions which I will share here. I can't take credit for it, all I did was rearrange some of the code and re-order the output (the original seemed backwards to me) but it is very nice. I am keeping it in the source code for the comic editor in case I ever need it again.

Here is the function. Calling it should be self-explanatory. Note that the colorCount parameter will be the total size of the output array INCLUDING the start and end colors.

function generateColorGradient(colorStart, colorEnd, colorCount) {

    /* Convert a hex string to an RGB triplet */
    var convertToRGB = function(hex) {

        /* Remove '#' in color hex string */
        var trim = function(s) {
            return (s.charAt(0) == '#') ? s.substring(1, 7) : s;

        var color = [];
        color[0] = parseInt((trim(hex)).substring(0, 2), 16);
        color[1] = parseInt((trim(hex)).substring(2, 4), 16);
        color[2] = parseInt((trim(hex)).substring(4, 6), 16);
        return color;


    /* Convert an RGB triplet to a hex string */
    var convertToHex = function(rgb) {

        var hex = function(c) {
            var s = "0123456789abcdef";
            var i = parseInt(c);
            if (i == 0 || isNaN(c))
                return "00";
            i = Math.round(Math.min(Math.max(0, i), 255));
            return s.charAt((i - i % 16) / 16) + s.charAt(i % 16);

        return hex(rgb[0]) + hex(rgb[1]) + hex(rgb[2]);


    var start = convertToRGB(colorStart);
    var end = convertToRGB(colorEnd);

    // The number of colors to compute
    var len = colorCount - 1;

    //Alpha blending amount
    var alpha = 0.0;

    var ret = [];

    for (i = 0; i < len; i++) {
        var c = [];
        alpha += (1.0 / len);
        c[0] = end[0] * alpha + (1 - alpha) * start[0];
        c[1] = end[1] * alpha + (1 - alpha) * start[1];
        c[2] = end[2] * alpha + (1 - alpha) * start[2];

    ret[len] = convertToHex(end); // last color might be slightly off

    return ret;


One thing that I noticed is that for colorCount values greater than 13 the final color was not quite the requested final color. Rounding error I suppose. That's why I explicitly set the last element in the return array to the end color, if you were wondering.

Using jQuery, I wrote a simple demonstration of the gradient function:

    var things = generateColorGradient("#CC0033", "#FFFF66", 15);
    for (var i = 0; i < things.length; i++) {
        $("body").append("<div style='background-color: #" + things[i] + ";'>test</div>");

...which produces the following output on a web page. Beautiful, isn't it?

Today's comic, on the other hand, contains absolutely nothing of any technical interest. You should still read it though. And if you haven't read all the other comics, what are you waiting for? They don't take that long to read. Start today! comic for 1 February 2016