PostADay-Round2#2 – Cinder/C++ Boid class port

It’s weird porting something that was written into, c++ ported to AS3, back to C++. However If you’ve ever tried to find the C++ version of a boids class. They’re all too complicated for my needs, and i really like the way @soulwire ‘s version works so I started porting it into C++. Based largely on my iOS port of the same class.

https://github.com/onedayitwillmake/CinderBoid

VIDEO DEMOS

WanderSeek

BoidTrailTest from mario gonzalez on Vimeo.

Basic Usage

.cpp

Creation

 
<code>
float boidMaxSpeed = 100;
float boidMaxForce = 25;
 
// Create
_boid = new Boid( boidMaxSpeed, boidMaxForce );
_boid-&gt;setPosition( _target.x, _target.y, _target.z );
 
// Set wander properties
_boid-&gt;setWanderRadius( 75.0f );
_boid-&gt;setWanderMaxTurningSpeed( M_PI / 32 ); // 
_boid-&gt;setWanderLookAheadDistance( 300 );
 
</code>

Update



_boid->wander( 0.3f );
_boid->seek( _mousePositionXYZ, 0.8f );
_boid->update();



PostADay-Round2#1 – Calculating surface normals in C++

Given a quad, this is how you can calculate the normals for each face.
This works for triangles, as well as quad.

Loop through each face, and pass in 3 verticies. If you have a quad ABCD pass in ABD. For example for the front facing face on this cube, I would pass in, v2, v3, v0

// cube ///////////////////////////////////////////////////////////////////////
//    v6----- v5
//   /|      /|
//  v1------v0|
//  | |     | |
//  | |v7---|-|v4
//  |/      |/
//  v2------v3

This is in C++ which supports operator overloading, so keep that in mind, when you see p2-p1, its doing: (p2.x-p1.x; p2.y-p1.y; p2.z-p1.z; )

// 
Vec3f RibbonMesh::calcNormal( const Vec3f &p1, const Vec3f &p2, const Vec3f &p3 )
{
    Vec3f V1= (p2 - p1);
    Vec3f V2 = (p3 - p1);
    Vec3f surfaceNormal;
    surfaceNormal.x = (V1.y*V2.z) - (V1.z-V2.y);
    surfaceNormal.y = - ( (V2.z * V1.x) - (V2.x * V1.z) );
    surfaceNormal.z = (V1.x-V2.y) - (V1.y-V2.x);
 
 
    // Dont forget to normalize if needed
    return surfaceNormal;
}

PostADay – Round2

I think i’m going to start writing one post per day, it was pretty fun experience last time, although i only made it about 2 weeks in.
This time I’m going to simply aim for 1 post per day, for 1 week.

As a programmer, I feel that I’m learning stuff everyday. If it wasn’t, then i wouldn’t be coding!
So it should be fairly easy to share one of those things each day.

Let’s see how i do

Post-A-Day #4 – Objective-C Flocking-Behaviors/Boid Class

This post a day thing is great, it’s really made me kick some stuff into gear.

I love flocking behaviors, they’re awesome.
What are Flocking Behaviors?


They were created in the 1980’s from by Criag Renolds, the gist of it is that using 3 simple behaviors, surprisingly complex motion can be formed when you have many actors ( Referred to as Boids, i think Craig meant it as a another way of saying Birds, a more new york way).


The three rules are simple, i’ll explain them as i know them but im no expert.
Separation: Boids want to stay a little away from each other, some elbow room.
Cohesion: Boids want to be grouped, as long as they dont get too close they violate rule 1
Alignment: Boids within a certain range, care about which way other boids are going.

Simple right? Anyway, it makes for very pretty stuff.


A few months ago a friend of mine gave a talk based on Kieth Peters book AdvancED ActionScript 3.0 Animation (a great book). This re-sparked my interest in them, and with my on going interest in iphone development – I decided to try and port Kieth Peters code to Objective-C as best I could with the more limited knowledge I had at the time.

It actually didn’t work all that great, but, I came across SoulWire’s interpretation of Flocking (also in AS3), and I ported that. Maybe it was because it was my second attempt at porting, but this time I got really great results.
200 Objects flocking, all aware of every single other one, on a tiny iphone in your hand, that was very rewarding.
The problem was that I used Box2D’s point class B2Vec2, and then i modified it a little to boot, because I wanted to add a few operators it didn’t have built in. So it left me with something I could not really share with anyone else, and also it was now Combining Objective-C and C++, which always seems like you should avoid it whenever possible.

This was many months ago (march according to my SVN), and i had my fun playing with it and left it at that.
However, recently on the Cocos2D forums someone brought up making a heat seeking missile and I mentioned that stearing behaviors would be a great for that, if maybe over complicated but being a game forum – you worry about that less as it might be a great jumping platform from which additional gameplay ideas stem.

I decided I would revisit my class, as I had been wanting to for a long time, and re-write it using only CGPoints so that it could be pure Objective-C.

This was the result:

LittleBirds from mario gonzalez on Vimeo.

Here’s how to use the class:

 
// Creating it
boid = [Boid spriteWithSpriteSheet:_sheet rect: boidRect];
[boid setSpeedMax: 2.0f andSteeringForceMax: 1.0f];
[boid setWanderingRadius: 16.0f lookAheadDistance: 40.0f andMaxTurningAngle:0.2f];
 
// On your update function
while(boid)
	{
		Boid* b = boid;
		boid = b->_next;
		[b wander: 0.19f];
		[b 
		 flock:_flockPointer
		 withSeparationWeight:0.6f
		 andAlignmentWeight:0.1f
		 andCohesionWeight:0.2f
		 andSeparationDistance:10.0f
		 andAlignmentDistance:30.0f
		 andCohesionDistance:20.0f
		 ];
 
		[b flee:badThingPosition panicAtDistance:5 usingMultiplier:0.6f]; // avoid touch
		[b seek:yummyFoodPosition withinRange:75 usingMultiplier:0.35f]; // go towards touch
                [b update];
	}

The class may be downloaded here:
BoidsExample Version 0.2

It’s coded to the best of my ability, if you have (impactful) optimizations please share.

Update #1:
Fixed Flocking example class linked list creation bug.

Simple rules combine to make seemingly complex behaviors: