coin - Dave's Blog

Considerate MessagePort Usage

When writing a JavaScript library that uses postMessage and the message event, I must be considerate of other JS code that will be running along side my library. I shouldn't assume I'm the only sender and receiver on a caller provided MessagePort object. This means obviously I should use addEventListener("message" rather than the onmessage property (see related What if two programs did this?). But considering the actual messages traveling over the message channel I have the issue of accidentally processing another libraries messages and having another library accidentally process my own message. I have a few options for playing nice in this regard:

Require a caller provided unique MessagePort

This solves the problem but puts a lot of work on the caller who may not notice nor follow this requirement.

Uniquely mark my messages

To ensure I'm acting upon my own messages and not messages that happen to have similar properties as my own, I place a 'type' property on my postMessage data with a value of a URN unique to me and my JS library. Usually because its easy I use a UUID URN. There's no way someone will coincidentally produce this same URN. With this I can be sure I'm not processing someone else's messages. Of course there's no way to modify my postMessage data to prevent another library from accidentally processing my messages as their own. I can only hope they take similar steps as this and see that my messages are not their own.

Use caller provided MessagePort only to upgrade to new unique MessagePort

I can also make my own unique MessagePort for which only my library will have the end points. This does still require the caller to provide an initial message channel over which I can communicate my new unique MessagePort which means I still have the problems above. However it clearly reduces the surface area of the problem since I only need once message to communicate the new MessagePort.

The best solution is likely all of the above.
Photo is Sharing by leezie5. Two squirrels sharing food hanging from a bird feeder. Used under Creative Commons license Attribution-NonCommercial-NoDerivs 2.0 Generic.

Cheap Multiplayer Tricks for New Super Mario Bros. Wii

The New Super Mario Bros. Wii is a great game. Its the fun of old school Mario with the addition of great graphics and the kind of multiplayer I've wanted for Mario since playing the original as a child: its got up to four player simultaneous cooperative multiplayer. I recommend it to anyone who has enjoyed Mario in the past. Watch this amazing video of level 1-3 you can unlock in the game.

As noted elsewhere, multiple players attempting to navigate platforms, grab power ups, and throw turtle shells creates new challenges but along with that there's new ways to be incredibly cheap.

Jumping Higher

A second player means a head one can jump on to reach higher locations. Jump on your friend's head at the apex of their jump while holding down the jump button yourself for maximum jumping. In the game you can also grab other players and hold them over your head. This is useful for reaching the top of the flagpole at the end of levels. On that same line, if the player you grab has a flying cap you can now use them to fly in the same manner you would use a flying block which makes it easy to get two players to the top of the finish flagpole if only one of you has a flying cap.

Power-Ups

Normal power-up blocks now spawn enough power-ups for everyone. A mushroom is spawned for each small player and full power-ups for the rest, except in the case everyone is small: then one of the power-ups is a full power-up. If there's two players and you're both small, the full power-up always jumps out of the block to the right. Some hidden power-up blocks only give out one power-up and in that case its a mushroom or not based on the player who hits the block - so be sure that a big player hits that if you have one.

Death & Bubbles

When a player dies but at least one other player lives the dead player comes back in a limbo bubble from which they must be released before they may play again. Because of this, in a tough spot you can send one player in and leave a second behind. If the first dies you don't lose your place in the level and the first comes back in a bubble ready to try again. For instance, if you're trying to get the last star coin in 2-1 which sits just above the abyss, one player can just jump to their death for it and as long as another player lives you've collected the coin. However you need not sacrifice your life to do this: you can press down and 'a' to force yourself into a bubble saving yourself from death. This is true in general as long as you have enough time to see your death coming. This is also useful if one player runs ahead to the right. The screen will expand a bit but then it will just move to the right following the player in the lead. Players left behind walls or now forced into lava pits will die unless they use the bubble.

Misc.

• If all players hit the ground at the same time from a ground pound it acts like hitting a pow block, killing the enemies on the screen.
• If you hold a player who has a projectile power over your head they can still use their power.
• Bubbles can be popped by hitting them with your fire or ice projectiles as well as thrown shells or blocks.
• All players get the extra lives from anyone collecting 100 coins or finishing a level with more than 7 enemies on the screen.

Platonic Ideals in Anathem and The Atrocity Archives

On the topic of made up words: I get made up words for made up things, but there's already a name for cell-phone in English: its "cell-phone". The narrator notes that the book has been translated into English so I guess I'll blame the fictional translator. Anyway, I wasn't bothered by the made up words nearly as much as some folk. Its a good thing I'm long out of college because I can easily imagine confusing the names of actual concepts and people with those from the book, like Hemn space for Hamming distance. Towards the beginning, the description of slines and the post-post-apocalyptic setting reminded me briefly of Idiocracy.

Recently, I've been reading everything of Charles Stross that I can, including about a month ago, The Jennifer Morgue from the surprisingly awesome amalgamation genre of spy thriller and Lovecraft horror. Its the second in a series set in a universe in which magic exists as a form of mathematics and follows Bob Howard programmer/hacker, cube dweller, and begrudging spy who works for a government agency tasked to suppress this knowledge and protect the world from its use. For a taste, try a short story from the series that's freely available on Tor's website, Down on the Farm.

Coincidentally, both Anathem and the Bob Howard series take an interest in the world of Platonic ideals. In the case of Anathem (without spoiling anything) the universe of Platonic ideals, under a different name of course, is debated by the characters to be either just a concept or an actual separate universe and later becomes the underpinning of major events in the book. In the Bob Howard series, magic is applied mathematics that through particular proofs or computations awakens/disturbs/provokes unnamed horrors in the universe of Platonic ideals to produce some desired effect in Bob's universe.

Moved

• Sarah's condo
• Storage
• My office
• Recycle/Donate

Office with a View