COCOS2DX中实现图层的惯性拖拽

苹果的应用讲究用户体验

有的时候仔细想想

的确，很多细节决定了用户体验

比如说惯性拖动

可以说之前没有任何一家厂商能把触摸惯性拖动做的像苹果的UI那么流畅

 

这次简单的写一下在Cocos2D中实现图层的惯性拖动

原理是简单模拟物理引擎的计算，通过改变力来改变图层的运动速度，以达到流畅的体验

直接上代码：

 

 

#import "cocos2d.h"

@interface DragLayer : CCLayer
{
    BOOL isDragging;//是否正在拖动
    CGPoint lastPosition;//上一个时间间隔时的图层位置
    CGPoint velocity;//图层移动速度
    CGPoint acceleration;//加速度
    CGPoint force;//受力
}

+(id) dragLayer ;

@end

#import "DragLayer.h"

@implementation DragLayer

-(id)init
{
　　if((self = [super init]))
　　{
        // 初始化图层
        self.isTouchEnabled = YES;
        isDragging = NO;
        lastPosition = CGPointZero;
        velocity = CGPointZero;
        acceleration = CGPointZero;
        force = CGPointZero;

        // 开启计时器
        [self scheduleUpdate];
    }
    return self;

    }
}

+(id) dragLayer;
{
    return [[[self alloc] init] autorelease];
}

-(void)update:(ccTime)delta
{

    // 如果没有被拖拽，模拟物体惯性
    if ( !isDragging )
    {
        CGPoint pos = self.position;

        // *** 通过在这里改变图层的受力，达到自然的惯性拖拽 *** //
        // 在这里，只添加一个方向和速度方向相反，大小和速度大小相同的阻力，一次不断减小速度，最终速度为零时，受力为零，物体静止 //
        force = ccpMult(velocity, -0.1);


        // 将受力计算为最终物体的移动
        acceleration = ccpMult(force,1);
        velocity = ccpAdd(velocity,acceleration);
        CGPoint change = ccpMult(velocity,dt);
        pos = ccpAdd(pos,change);
        self.position = pos;
    }
    // 如果正在拖拽，记录下拖拽时图层的移动速度
    else
    {
        velocity= ccpSub(self.position,lastPosition);
        lastPosition= self.position;
    }
}

-(void)registerWithTouchDispatcher
{
   [[CCTouchDispatcher sharedDispatcher] addTargetedDelegate:self priority:1 swallowsTouches:YES];
}

-(BOOL)ccTouchBegan:(UITouch *)touch withEvent:(UIEvent *)event
{
    // 标记为正在拖拽
   isDragging = YES;
   return YES;
}

-(void)ccTouchMoved:(UITouch *)touch withEvent:(UIEvent *)event
{
    // 根据触摸点位移改变图层位置
    CGPoint a = [[CCDirector sharedDirector] convertToGL:[touch previousLocationInView:touch.view]];
    CGPoint b = [[CCDirector sharedDirector] convertToGL:[touch locationInView:touch.view]];
    CGPoint change = ccpSub(b,a);
    self.position = ccpAdd(self.position,change );

    return;
}

-(void)ccTouchesEnded:(NSSet *)touches withEvent:(UIEvent *)event
{
    // 结束拖拽，标记为未拖拽
    isDragging = NO;
    return;
}

- (void) dealloc
{
    // in case you have something to dealloc, do it in this method
    // in this particular example nothing needs to be released.
    // cocos2d will automatically release all the children (Label)

    // don't forget to call "super dealloc"
    [super dealloc];
}

@end