Box2Dを使って、坂を転がってくるトロッコをジャンプさせる簡単なゲームをiPhoneアプリとして書いてみます。坂の角度を指で変更できるようにして、遠くにジャンプさせたり、ちょっとだけしかジャンプしないようにとあそんでみましょう。
動作イメージ
XcodeからiOS6 iPhone Simulatorで動かすとこんな感じになります。
Box2d導入手順（覚え書き）
1. Box2DのサイトのDownloadからソースを取得する
2 Box2Dをプロジェクトに追加
3. C++ で書く。Box2dを使うソースの拡張子を .mm に
4. Build Settings (All) の Header Search PathsにBox2Dを配置したフォルダを指定
サンプルコード
#import “ViewController.h”
#import <QuartzCore/QuartzCore.h>
#import <Box2D/Box2D.h>
#define PixelToMeter_RATIO 16.0
#define screen CGSizeMake(568, 300)
@interface ViewController () {
b2World *world;
b2Body *slopeBody;
CAShapeLayer *sl;
NSTimer *timer;
CGPoint slopeTop;
}
@end
@implementation ViewController
– (void)viewDidLoad
{
[super viewDidLoad];
self.view.backgroundColor = [UIColor blueColor];
[self createWorld];
[self createSlope:200];
[self createCart];
[self start];
}
– (void)createWorld
{
b2Vec2 gravity;
gravity.Set(0.0f, –9.81f);
world = new b2World(gravity);
world->SetContinuousPhysics(true);
b2BodyDef groundBodyDef;
groundBodyDef.position.Set(0, 0);
b2Body* groundBody = world->CreateBody(&groundBodyDef);
b2EdgeShape groundBox;
groundBox.Set(b2Vec2(0,0), b2Vec2(screen.width/PixelToMeter_RATIO, 0));
groundBody->CreateFixture(&groundBox, 0);
}
– (void)createSlope:(float)height
{
slopeTop = CGPointMake(0, height);
CGPoint bottom = CGPointMake(200, 300);
CGPoint jump0 = CGPointMake(260, 300);
CGPoint jump1 = CGPointMake(280, 280);
// view
[sl removeFromSuperlayer];
UIBezierPath *path = [UIBezierPath bezierPath];
CGPoint p[] = {slopeTop, bottom, jump0, jump1};
for (int i=0; i<2; i++) {
[path moveToPoint:p[i * 2]];
[path addLineToPoint:p[i * 2 + 1]];
}
sl = [[CAShapeLayer alloc] init];
sl.fillColor = [UIColor blackColor].CGColor;
sl.strokeColor = [UIColor blackColor].CGColor;
sl.lineWidth = 5;
sl.path = path.CGPath;
[self.view.layer addSublayer:sl];
if (slopeBody) {
world->DestroyBody(slopeBody);
}
b2BodyDef groundBodyDef;
groundBodyDef.position.Set(0, 0);
slopeBody = world->CreateBody(&groundBodyDef);
b2EdgeShape s1;
s1.Set(b2Vec2(slopeTop.x, (screen.height – slopeTop.y)/PixelToMeter_RATIO), b2Vec2(bottom.x /PixelToMeter_RATIO, (screen.height – bottom.y)/PixelToMeter_RATIO));
slopeBody->CreateFixture(&s1, 0);
b2EdgeShape ground;
ground.Set(b2Vec2(jump0.x /PixelToMeter_RATIO, 0), b2Vec2(jump1.x /PixelToMeter_RATIO, (screen.height – jump1.y)/PixelToMeter_RATIO));
slopeBody->CreateFixture(&ground, 0);
}
– (void)createCart
{
// cart body
UIView *v = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 60, 10)];
v.center = CGPointMake(20, 0);
v.backgroundColor = [UIColor orangeColor];
[self.view addSubview:v];
b2FixtureDef fixtureDef;
fixtureDef.density = 1.0f;
fixtureDef.friction = 0.3f;
fixtureDef.restitution = 0.1f;
b2Body *cartBody = [self addPhysicalBodyForBoxView:v type:fixtureDef];
cartBody->SetLinearVelocity(b2Vec2(10.0, –80.0));
// tires
for (int i=0; i<2; i++) {
UIView *tire = [[UIView alloc] initWithFrame:CGRectMake(0, 0, 20, 20)];
tire.backgroundColor = [UIColor blackColor];
tire.layer.cornerRadius = 9.0;
tire.center = CGPointMake(20 + i *20, 25);
[self.view addSubview:tire];
b2Body *tireBody = [self addPhysicalBodyForCircleView:tire type:fixtureDef];
b2RevoluteJointDef revoluteJointDef;
revoluteJointDef.bodyA = cartBody;
revoluteJointDef.bodyB = tireBody;
revoluteJointDef.collideConnected = false;
revoluteJointDef.localAnchorA.Set(-1.0 + i * 2.0, 0);
revoluteJointDef.localAnchorB.Set(0,0);
world->CreateJoint(&revoluteJointDef);
}
}
– (b2Body*)addPhysicalBodyForBoxView:(UIView *)physicalView type:(b2FixtureDef)fixtureDef
{
// Define the dynamic body.
b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
CGPoint p = physicalView.center;
CGPoint boxDimensions = CGPointMake(physicalView.bounds.size.width/PixelToMeter_RATIO/2.0, physicalView.bounds.size.height/PixelToMeter_RATIO/2.0);
bodyDef.position.Set(p.x/PixelToMeter_RATIO, (screen.height – p.y)/PixelToMeter_RATIO);
bodyDef.userData = (__bridge void *)physicalView;
b2Body *body = world->CreateBody(&bodyDef);
b2PolygonShape dynamicBox;
dynamicBox.SetAsBox(boxDimensions.x, boxDimensions.y);
fixtureDef.shape = &dynamicBox;
body->CreateFixture(&fixtureDef);
body->SetType(b2_dynamicBody);
return body;
}
– (b2Body*)addPhysicalBodyForCircleView:(UIView *)physicalView type:(b2FixtureDef)fixtureDef
{
// Define the dynamic body.
b2BodyDef bodyDef;
bodyDef.type = b2_dynamicBody;
CGPoint p = physicalView.center;
bodyDef.position.Set(p.x/PixelToMeter_RATIO, (screen.height – p.y)/PixelToMeter_RATIO);
bodyDef.userData = (__bridge void *)physicalView;
b2Body *body = world->CreateBody(&bodyDef);
b2CircleShape circle;
circle.m_radius = physicalView.bounds.size.width/PixelToMeter_RATIO/2.0;
fixtureDef.shape = &circle;
body->CreateFixture(&fixtureDef);
body->SetType(b2_dynamicBody);
return body;
}
– (void)start
{
// タイマーをスタート
timer = [NSTimer scheduledTimerWithTimeInterval:1.0f/60.0f target:self selector:@selector(tick:) userInfo:nil repeats:YES];
}
– (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
CGPoint p = [[touches anyObject] locationInView:self.view];
[self createSlope:p.y];
}
– (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
[self createCart];
}
-(void) tick:(NSTimer *)sender
{
int32 velocityIterations = 8;
int32 positionIterations = 1;
world->Step(1.0f/60.0f, velocityIterations, positionIterations);
for (b2Body* b = world->GetBodyList(); b; b = b->GetNext())
{
if (b->GetUserData() != NULL)
{
UIView *oneView = (__bridge UIView *)b->GetUserData();
CGPoint newCenter = CGPointMake(b->GetPosition().x * PixelToMeter_RATIO, self.view.bounds.size.height – b->GetPosition().y * PixelToMeter_RATIO);
oneView.center = newCenter;
CGAffineTransform transform = CGAffineTransformMakeRotation(- b->GetAngle());
oneView.transform = transform;
}
}
}
– (void)didReceiveMemoryWarning
{
[super didReceiveMemoryWarning];
// Dispose of any resources that can be recreated.
}
@end