做了一个简单的 SceneKit 场景，即加载动画，并控制动画人物行走，保持摄像机跟随。。。。
最终效果:
git 传送门 : https://github.com/eassy/TimoRun

创建一个手柄控制板

这是控制板最终的样式，中间的按钮只会在触碰的时候显示出来，而且随着手指的移动，中间的按钮在大圈范围内跟随移动。
自定义一个 UIView ，利用 touchBegin 等一系列的事件检测方法，将触碰点捕捉到，同时判断触碰点是否在大圈范围内，在的话将按钮中心位置挪到触碰点处，不在的话，将按钮中心位置挪到跟触碰点在一个方向的大圈圆周这个点处。有难度的可能是计算按钮中心点最终所处的位置。 

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- (CGFloat)lengthFromA:(CGPoint)aPoint toB:(CGPoint)bPoint
{
    return sqrt((aPoint.x - bPoint.x)*(aPoint.x-bPoint.x) + (aPoint.y-bPoint.y)*(aPoint.y-bPoint.y));
}

- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    self.pad.hidden = NO;
    
    CGPoint point = [[touches anyObject] locationInView:self];
    
    [self movePadCenterToPoint:point animation:NO complete:^{
        
    }];
}

- (void)touchesMoved:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    CGPoint point = [[touches anyObject] locationInView:self];
    
    [self movePadCenterToPoint:point animation:NO complete:^{
        
    }];
}

- (void)touchesEnded:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    
    [self movePadCenterToPoint:CGPointMake(_bigRadius, _bigRadius) animation:YES complete:^{
        self.pad.hidden = YES;
    }];
    
}

- (void)touchesCancelled:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    [self movePadCenterToPoint:CGPointMake(_bigRadius, _bigRadius) animation:YES complete:^{
        self.pad.hidden = YES;
    }];
}

- (void)movePadCenterToPoint:(CGPoint)point animation:(BOOL)animation complete:(void(^)(void))completeBlock
{
    CGFloat length = [self lengthFromA:point toB:CGPointMake(_bigRadius, _bigRadius)];
    CGPoint finalPoint;
    if (length < _bigRadius - _smallRadius) {
        finalPoint = point;
    }
    else{
        
        //计算应该的 center
        CGFloat a = (point.x - _bigRadius)/(point.y - _bigRadius);
        CGFloat l = _bigRadius - _smallRadius;
        
        CGFloat offsetY = sqrt(l * l/(a * a + 1));
        if (point.y >= _bigRadius) {
            finalPoint.y = offsetY + _bigRadius;
        }
        else{
            finalPoint.y = _bigRadius - offsetY;
        }
        finalPoint.x = a * (finalPoint.y - _bigRadius) + _bigRadius;
    }
    
    if (!isnan(finalPoint.x) && !isnan(finalPoint.y)) {
        self.pad.center = finalPoint;
    }
    
    if (completeBlock) {
        completeBlock();
    }
    
    if ([self.delegate respondsToSelector:@selector(padControl:toPoint:)]) {
        [self.delegate padControl:self toPoint:CGPointMake(finalPoint.x - _bigRadius, finalPoint.y - _bigRadius)];
    }
}

计算公式不难，大圆中心点位置为 (_bigRadius,_bigRadius),设大圆中心点为(x1,y1),触碰点位置为(x2,y2),最终点为(x,y)，则可列公式:

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//bigRadius:大圆半径  smallRadius:小圆半径
(x-x1)/(y-y1) = (x2-x1)/(y2-y1)
(x-x1)² + (y-y1)² = (_bigRadius - smallRadius)²
令 l = _bigRadius - _smallRadius;  
   a = (point.x - _bigRadius)/(point.y - _bigRadius);
由此可得 offsetY = |y-y1| = sqrt(l * l/(a * a + 1));
再根据触碰点相对于中心点的方向信息，得出 finalY，最终得出 finalX

加载文件中的动画和人物

因为资源文件是带动画的，所以取出来时要先 remove 掉，先保存，后 remove。

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- (void)makeTimo
{
    SCNScene *timoScene = [SCNScene sceneNamed:@"art.scnassets/TiMo.DAE"];
    
    self.timoNode = [SCNNode node];
    
    for (SCNNode *childNode in timoScene.rootNode.childNodes) {
        
        [self.timoNode addChildNode:childNode];
        if (childNode.animationKeys.count) {
            self.walkAnimation = [childNode animationForKey:childNode.animationKeys[0]];
            self.walkAnimation.speed = 1.5;
            [childNode removeAllAnimations];
        }
    }
    
    self.timoNode.position = SCNVector3Make(0, 0.15, 0);
    self.timoNode.scale = SCNVector3Make(0.2, 0.2, 0.2);
    
    SCNPhysicsBody *timoBody = [SCNPhysicsBody kinematicBody];
    timoBody.mass = 10;
    
    self.timoNode.physicsBody = timoBody;
    [self.mainScene.rootNode addChildNode:self.timoNode];
     
}

物理身体的类型我设置成了 kinematicBody ，因为 设置成动态身体的话根本站不住。。。软趴趴倒在地上哈哈哈。可以看到我将动画保存了起来，然后 remove 掉了。

创建 Camera 和灯光

有两个 Camera ，一个是位置一直跟随人物移动的 camera，一个是一直面向人物，但是位置不变的，通过双击屏幕切换这两个视角。

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- (void)setupCamera
{
    // create and add a camera to the scene
    SCNNode *cameraNode = [SCNNode node];
    cameraNode.camera = [SCNCamera camera];
    [self.mainScene.rootNode addChildNode:cameraNode];
    
    // place the camera
    cameraNode.position = SCNVector3Make(0, 50, 60);
    cameraNode.rotation = SCNVector4Make(1, 0, 0, -M_PI / 6.f);
    cameraNode.camera.zFar = 2000;
    self.cameraNode = cameraNode;
    
    ((SCNView *)self.view).pointOfView = self.cameraNode;
    
    SCNNode *thirdCameraNode = [SCNNode node];
    thirdCameraNode.camera = [SCNCamera camera];
    [self.mainScene.rootNode addChildNode:thirdCameraNode];
    thirdCameraNode.position = SCNVector3Make(0, 50, 120);
    thirdCameraNode.rotation = SCNVector4Make(1, 0, 0, -M_PI / 6.f);
    thirdCameraNode.camera.zFar = 2000;
    SCNLookAtConstraint *constraint = [SCNLookAtConstraint lookAtConstraintWithTarget:self.timoNode];
    thirdCameraNode.constraints = @[constraint];
    self.thirdCameraNode = thirdCameraNode;
    
}

初始的视角是跟随的摄像机。
我添加了一个环境光，八个聚焦灯(后面我超想用聚焦灯创建一个ktv那种球状灯的)，灯的方向都是照向地面。

创建环境

创建地板

创建地板的时候并没有指定大小，好像默认无限大了？

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- (void)makeFloor
{
    SCNNode*floor = [SCNNode node];
    floor.geometry = [SCNFloor floor];
    floor.geometry.firstMaterial.diffuse.contents = @"art.scnassets/moss_diffuse.png";
    floor.geometry.firstMaterial.diffuse.contentsTransform = SCNMatrix4MakeScale(2, 2, 1); //scale the wood texture
    floor.geometry.firstMaterial.locksAmbientWithDiffuse = YES;
    
    SCNPhysicsBody *staticBody = [SCNPhysicsBody staticBody];
    floor.physicsBody = staticBody;
    
    [self.mainScene.rootNode addChildNode:floor];
}

创建四面墙

创建两面墙，然后使用 clone ，rotate,position 等将墙放在合适的位置。每面墙都是静态躯体。

创建一个足球

创建一个球，设置动态物理身体，然后可以被踢着走了~