The game is based on the XNA sample game “Catapult Wars Lab”. We’ll reuse the assets from that game as we develop a new version for Windows 8 that’s based on web technologies.
In this post, we’ll respond to user input and make things a bit more lively by adding sound.
Handling User Input
Of course there are many ways we could have shot aiming work – random, time-based, precision-based (e.g. “click… NOW!”), but in this case we’ll let the user draw a line indicating both direction and speed.
First, let’s add new variables near the top of
Windows 8 supports several ways to draw – mouse, touch, pen – and our game needs to be flexible enough to support whichever the user has. Fortunately, the MSPointer system combines support for all of these into one. We’ll use
MSPointerDown/Up to begin and end aiming, plus
MSPointerMove to provide feedback as the user adjusts the aim.
By the way, there’s also great support via
MSGesture for detecting gestures such as tap, double-tap, etc. A good example for handling input and gestures is the “BallInEight” sample on MSDN.
These events are used by pointing to listener functions, called when they fire. Let’s take care of that now, adding near the top of the
And now for the functions themselves: add where you like, but I placed between
Note an exercise is left here. For simplicity, I omitted showing text with aim % and/or drawing an aiming arrow during the
adjustAim() function. Go ahead and try adding that – from earlier parts, we’re already using the very same techniques you’ll need.
And a function to help us calculate the aim:
Again, simplicity rules the day and this is only for player 1, but here’s what’s happening:
- Lines 239-241 – Create a new
Pointfrom the distance from the start to end
Points. Scale it down to a good velocity to apply per frame/update.
- Lines 242 & 244 – Make sure the
yare limited so the shot doesn’t simply disappear off the screen, going too quickly
- Lines 243 & 245 – Make sure the shot is going toward the enemy … more or less.
We earlier added some temporary code to
update() to have player 1 always fire randomly. Now we can replace that to use the new
Go ahead and run the game…
Now you can use the mouse, pen, or touch to control the shot!
“I must be hearing things!” – Adding Sound
Our job as a game dev isn’t done until we have some sound. We’ve already added the sound files back in Part 2 so let’s take the next step by loading them.
First, a few variables in
default.js to keep things tidy:
Recall from Part 2 that we’ve already wired up
PreloadJS to ensure our resources are ready when the game starts? We can use the same approach with sounds, so let’s add them to the manifest:
To use these files, we’ll create instances of HTML
Note, we will not be using SoundJS (another part of CreateJS) in this example, but of course you’re welcome to take it for a spin!
playSound(file) helper function:
That’s it! Now we just call it, specifying the constant pointing to the right file. We’ll do this in several places.
First, add a call to
As the comment mentions, you could use the “Hit” sound instead of “Explode” if you’d like to have it take multiple hits to destroy a catapult.
And finally, play end win or lose sound in
Go ahead and give it a run to try things out.
Game On… And On… And On…
Congratulations! You’ve made a game!
We’ve covered a lot of ground in these posts, but like anything, there’s plenty of other things to try. Why not take a stab at some of them?
- Screen adjustments – Portrait/landscape, snapped/filled. A great chance to learn about CSS Media Queries!
- Improving Touch/Gesture support
- Sprites/animations – Shot hit/miss, catapult pullback/fire, catapult destroyed
- Gameplay dynamics – Adding wind, new scenes, new catapult features/upgrades, choices in ammo, etc.
- Add a mountain and moving clouds to background (the assets are already there)
- Add some intelligence to the currently very artificial intelligence
- Consider using a live tile – Maybe show the player’s last/high score?
Enjoy! Looking forward to hearing about the awesome new things you add!
Chris Bowen is a Principal Technical Evangelist with Microsoft, based in the Boston area and specializing in Windows 8 development. An architect and developer with over 19 years in the industry, he joined Microsoft after holding senior technical positions at companies including Monster.com, VistaPrint, and Staples. He is coauthor of two books (with Addison-Wesley and WROX) and holds an M.S. in Computer Science and a B.S. in Management Information Systems, both from Worcester Polytechnic Institute.