NoshBar's Dumping Ground

Bridge Builder tutorial progress.

(click the image for a larger version)

Download the source code and either add the files to a Visual Studio Win32 solution that links to SDL and Box2D, or on Linux do:

g++ main.cpp -lSDL -lBox2D

Progress

While this is by no means THE bridge builder tutorial (I intend on writing LOTS and making many pretty pictures), this shows the direction I'm going.

I'm not sure if I should start things really simple and build up, or if I should assume prior knowledge of renderers and physics engines (not that I know much about either of those anyway).
I guessed that something like this would be a good start, then the next version would add images, show how to build for every platform under the sun, that kind of thing.

If anyone is reading this and by the same miracle is actually waiting to see what I come up with, I'd love to hear what you'd like to see.

Burning Built Bridges.

Once again I find myself building an effigy of my sorry self with the intent of beating it with a poo-covered hindsight stick.

I move to Sweden, finally get settled in, get my first ever iPhone, launch up the AppStore in Swedish and... BAM, two bridge building games in the top charts: Fat Birds and Bridge Constructor.

On the one hand I think "Oh well, I'd probably never have finished mine anyway", on the other hand I think "I can make a better one!", and on my other radioactive hand I think "CURSED OFFSPRING OF FEMALE CANINES!".

It's about time I admit to myself that I will never make a full game, finishing is haaard.

So I figured I'd refocus my efforts and give them a new name, putting a positive spin on things.

"Tutorial" = unfinished product that people appreciate.
Hopefully.

If I ever finish it, I will be putting up a tutorial on how to code a simple bridge building game in baby C++ (classes, no STL, blah).

With it, I may as well make an attempt to describe how I personally manage using the same code-base for Windows/Linux/OSX/iOS/Android/WebOS/BlackBerry(QNX).

The worst that can happen is I finally feel like I did something worthwhile, right?

Bridge Building Game update - 26 September 2009

Added a car to the mix (final version will have trains, planes, and monkeys [probably])
Made the bridge less bouncy
Tested building a bridge across a gap without fixed points

I'm going to add a "well done, you made it" message thingy
Some sort of explosion for when the top and front of the car experience extreme forces.

Saw an interesting post on the Box2D forums about hanging heavy objects from light objects, and how that's probably a bad thing, so I'll have to check that the bridge doesn't end up doing that during the game.

Also came across this interesting post on the Cocos2D forums about static analysis:
http://www.cocos2d-iphone.org/forum/topic/1662
the links contained within are handy for stoopid people like me.

Bridge Builder Update - 30 August

It might not seem like I did much, for this weeks update, but loads under the hood has changed.

I learnt that the size of the Box2D world has an enormous affect on the speed of the simulation, so I've simply divided by 10 to keep the world smaller.
As such, I've got to re-tweak the physics of the bridge elements, as the bridge is now waaay too elasticy.
I couldn't for the life of me figure out how to make the parallax zoom in on the middle focal point of the screen using Cocos2D's Parallax Node, so I simply implemented parallax scrolling myself.
I started just changing the Menu text to "Play Game", but got carried away and made a lame intro screen.

Bridge Builder Update - 16 August 2009

Just minor tests this week:

test menu system, want to make it into a nice expanding sun, and highlight the ray that's selected
test pin moving and editing "widget"

The only sensible way to create bridge segments is for the user to put a finger down on the start joint, and drag to the desired position, then let go.

The only problem is, you can't possibly accurately position the pin underneath your finger.
So I figure: create it inaccurately, and drag it with the widget afterwards (which should hopefully give a clear view of the pin).

I'm also mighty jealous of Moto X Mayhem's graphics and parallax scrolling.

Tile map editor for Bridge Builder prototype

Summary: this week I used Tiled to create a map for a parallax game level in Cocos2D, processing it with a custom written tool to calculate the Box2D collision area for the map automatically.

Tiled is a nice and portable tile map editor
There is a plugin here to export the level data to a TGA file that Cocos2D expects.
The plugin expects 3 layers, "tile", "bkgr" and "code"
I use the tile layer to store graphical tiles
Any tile in the code level is used to signify the tile it covers is collidable
The plugin exports "tile" data to the Red channel
The plugin exports "code" data to the Blue channel
Cocos2D only uses the Red channel
I wrote a poorly coded tool to calculate
1) from left to right, the first tile in each column that is collidable, and stores that row value as the first Green value in the row
2) the first collidable pixel on the left in the selected tile, which is stored in the second Green value in the row
3) the first collidable pixel on the right in the selected tile, which is stored in the third Green value in the row
In the app, a static edge object is created from vertices calculated from TileYOffset + TileYOffet information
(or at least it would add static edges, if they weren't acting funky... so instead, I create a 4 sided poly object per column for now)
For kicks, I added some parallax layers, the sky as the background, the level as the focal point, and the sea as the forefront layer.

Get the source here.

Box2D Bridge Joint experiments.

In order to finally start iPhone development, I decided to start with something I would enjoy, required the least amount of Objective C fiddling, and had a graphics API I was familiar with, OpenGL.

Enter left, the bridge building game. The physics are beyond my capabilities, so I figured Box2D would be just what I wanted.
Turns out, you still need to have a brain, nuts.

When I first started, I used the Box2D bridge testbed as a starting point, where it creates bridge segments, connected by revolution joints.
This works fine if all you're doing is creating a single layer of bridge segments to go from one side to the next.
The problem comes when you try add support structures, as you cannot add 3 bodies to one joint, as seen below.

Mnem was kind enough to suggest swapping the roles, replacing the bodies with distance joints, and the joints with bodies to hold them together.
This works great, as you can use the distance or reaction force of the joint to snap the joint when the force is too great.
The problem with this, is that you can't collide with a joint, so any vehicle travelling over the bridge would just fall through the structure segments.

My latest thinking involves a mixture of distance and revolution joints, and bodies acting in different roles.
So for the main structure segments, that the vehicle will travel over, you have a pin(body), connected to a joint(revolution), which is in turn connected to a structure segment, and/or a support joint(distance).
This means that the bridge is still flexible, can still be supported, and can still break, without uneven tension across its structure.

Learning Objective-C with the Bridge Builder prototype

A day late, but it was my first attempt at all this Objective C nonsense.

It's a simple bridge builder prototype, where you have a canyon, a vehicle, and some building materials to build a bridge with, in order to get the car to the other side.
It worked out remarkably well, so I think I'll develop it further in a proper game.
There are so many "feels right" values in it, and I wonder if I should perform some sort of proper tension simulation with "real" values in... but if it feels good, -hey-.

The Box2D iPhone TestBed by Simon Oliver (of Rolando fame) was such a great starting block, it made developing this fun.
I checked out Box2D revision 2.0.2 from SVN, and used the tags folder, mostly because I didn't know where to start, and the SVN tag had an iPhone project in it.

The Box2D framework side remains largely untouched, I just played with a few values to get things how I wanted them, and made the mousedown callback return true if it had consumed the event.
Get the code here.