我正在使用SpriteKit拍摄射弹。使用-(void)applyImpulse:(CGVector)impulse给予射弹节点一个冲动。
我想计算射弹在撞击地面之前飞行的距离，这可以很容易地知道射弹节点物理体的速度矢量和重力加速度（见Wikipedia: Range of a Projectile）。
然而，不清楚这个距离的单位是什么以及它们如何转换为SKScene中的距离。 SKPhysicsBody的{{1}}速度属性documentation没有提到单位。我目前正在运行一些测试来确定单位并映射到SKScene。
有没有人想出来的？
答案 0 :(得分：4)
单位可能是CGPoints / second
我通过打印位置变化/时间变化并将其与物理体的速度属性进行比较来做了一些实验。这是我的代码：
func moveInDirection(direction:CGVector, timeInterval:NSTimeInterval){
physicsBody?.linearDamping = damping
let changeInX = position.x-previous_whale_position.x
let changeInY = position.y-previous_whale_position.y
let x_Velocity = changeInX/CGFloat(timeInterval)
let y_Velocity = changeInY/CGFloat(timeInterval)
println("the m/svelocity \(physicsBody!.velocity.dx), \(physicsBody!.velocity.dy)")
println("the cgpointvelocity \(x_Velocity), \(y_Velocity)")
println()
physicsBody!.applyImpulse(direction*accelerationMultiplier)
physicsBody!.velocity = physicsBody!.velocity.limitToHypot(maxVelocity)
}
这是日志中的一些输出
the m/svelocity -419.904, -114.774
the cgpointvelocity -411.577, -112.497
the m/svelocity -410.107, -134.854
the cgpointvelocity -522.235, -171.725
the m/svelocity -406.494, -155.742
the cgpointvelocity -413.777, -158.531
the m/svelocity -395.372, -182.136
the cgpointvelocity -396.967, -182.874
the m/svelocity -389.263, -194.851
the cgpointvelocity -397.426, -198.937
the m/svelocity -384.932, -203.273
the cgpointvelocity -388.112, -204.951
the m/svelocity -383.476, -206.006
the cgpointvelocity -390.179, -209.609
the m/svelocity -382.996, -206.897
the cgpointvelocity -389.749, -210.543
the m/svelocity -382.839, -207.188
the cgpointvelocity -385.678, -208.726
the m/svelocity -382.787, -207.283
the cgpointvelocity -386.198, -209.131
the m/svelocity -382.77, -207.314
the cgpointvelocity -386.386, -209.272
the m/svelocity -382.765, -207.325
the cgpointvelocity -387.465, -209.871
the m/svelocity -382.763, -207.328
the cgpointvelocity -387.539, -209.915
the m/svelocity -382.762, -207.329
the cgpointvelocity -388.23, -210.291
the m/svelocity -385.052, -203.045
the cgpointvelocity -396.597, -209.134
the m/svelocity -404.03, -171.534
the cgpointvelocity -300.013, -127.373
the m/svelocity -411.441, -130.726
the cgpointvelocity -522.956, -166.157
the m/svelocity -422.1, -106.413
the cgpointvelocity -427.514, -107.779
the m/svelocity -425.415, -92.2759
the cgpointvelocity -430.583, -93.3979
the m/svelocity -431.763, -55.4343
the cgpointvelocity -451.494, -57.9693
the m/svelocity -438.175, -25.8145
the cgpointvelocity -327.677, -19.3046
the m/svelocity -435.305, 1.48222
the cgpointvelocity -431.963, 1.46786
the m/svelocity -431.347, 17.6925
the cgpointvelocity -555.525, 22.7858
the m/svelocity -434.409, 27.9586
the cgpointvelocity -435.048, 27.9997
the m/svelocity -432.63, 48.2073
the cgpointvelocity -437.134, 48.7081
the m/svelocity -431.843, 54.8057
the cgpointvelocity -440.961, 55.9637
the m/svelocity -430.199, 66.49
the cgpointvelocity -440.097, 68.0202
the m/svelocity -432.777, 73.2641
the cgpointvelocity -321.332, 54.3979
the m/svelocity -424.901, 76.3717
the cgpointvelocity -540.091, 97.0769
the m/svelocity -427.745, 80.7875
the cgpointvelocity -433.12, 81.8004
the m/svelocity -424.632, 95.811
the cgpointvelocity -431.081, 97.2632
the m/svelocity -423.5, 100.698
the cgpointvelocity -429.958, 102.232
the m/svelocity -423.118, 102.293
the cgpointvelocity -434.132, 104.954
the m/svelocity -426.516, 103.671
the cgpointvelocity -316.766, 76.9931
the m/svelocity -419.455, 102.133
the cgpointvelocity -533.238, 129.839
the m/svelocity -422.936, 103.04
the cgpointvelocity -429.117, 104.546
the m/svelocity -409.127, 99.6756
the cgpointvelocity -415.2, 101.156
the m/svelocity -395.769, 96.4212
the cgpointvelocity -399.771, 97.3951
the m/svelocity -382.847, 93.273
the cgpointvelocity -387.945, 94.5152
the m/svelocity -370.347, 90.2276
the cgpointvelocity -374.075, 91.1383
the m/svelocity -358.255, 87.2816
the cgpointvelocity -363.762, 88.6238
the m/svelocity -346.558, 84.4319
the cgpointvelocity -350.016, 85.275
the m/svelocity -335.243, 81.6751
the cgpointvelocity -350.701, 85.4411
the m/svelocity -326.999, 79.6668
the cgpointvelocity -242.241, 59.0151
the m/svelocity -313.709, 76.4288
the cgpointvelocity -404.319, 98.5007
the m/svelocity -305.995, 74.5495
the cgpointvelocity -225.667, 54.9776
the m/svelocity -293.558, 71.5194
the cgpointvelocity -380.591, 92.7216
the m/svelocity -286.339, 69.7608
the cgpointvelocity -217.244, 52.9272
the m/svelocity -276.99, 67.4831
the cgpointvelocity -273.834, 66.7158
the m/svelocity -265.732, 64.7403
the cgpointvelocity -338.328, 82.4244
the m/svelocity -257.056, 62.6265
the cgpointvelocity -265.84, 64.7653
the m/svelocity -250.735, 61.0865
the cgpointvelocity -188.673, 45.9667
the m/svelocity -242.548, 59.092
the cgpointvelocity -242.195, 59.0063
the m/svelocity -232.69, 56.6902
the cgpointvelocity -302.26, 73.6413
the m/svelocity -226.968, 55.2963
the cgpointvelocity -166.956, 40.6744
the m/svelocity -217.743, 53.0488
the cgpointvelocity -287.069, 69.9373
the m/svelocity -212.389, 51.7444
the cgpointvelocity -158.363, 38.5817
the m/svelocity -205.455, 50.0549
the cgpointvelocity -204.966, 49.9354
the m/svelocity -197.104, 48.0204
the cgpointvelocity -254.568, 62.0196
the m/svelocity -192.257, 46.8396
the cgpointvelocity -143.343, 34.9233
the m/svelocity -184.443, 44.9358
the cgpointvelocity -234.465, 57.1213
the m/svelocity -178.421, 43.4686
the cgpointvelocity -179.961, 43.8436
the m/svelocity -172.595, 42.0494
the cgpointvelocity -177.962, 43.3537
the m/svelocity -168.351, 41.0154
the cgpointvelocity -125.254, 30.5169
the m/svelocity -161.509, 39.3484
the cgpointvelocity -204.98, 49.9368
the m/svelocity -156.235, 38.0636
the cgpointvelocity -159.304, 38.8082
the m/svelocity -151.134, 36.8208
the cgpointvelocity -156.913, 38.2251
the m/svelocity -147.418, 35.9154
the cgpointvelocity -109.618, 26.7046
the m/svelocity -142.605, 34.7428
the cgpointvelocity -143.35, 34.9249
the m/svelocity -136.809, 33.3307
the cgpointvelocity -176.614, 43.0291
the m/svelocity -133.445, 32.5111
the cgpointvelocity -99.8049, 24.3138
the m/svelocity -128.021, 31.1897
the cgpointvelocity -165.016, 40.2001
the m/svelocity -124.873, 30.4228
the cgpointvelocity -93.041, 22.6676
所以我得出结论，距离单位几乎是cgpoints /秒..当前速度似乎并不能很好地代表实际速度。这可能归因于以下事实：在物理模拟期间测量m / s速度并且在更新功能期间测量cgpoint /秒速度，在不同时间间隔上进行测量。然而，m / s速度似乎平均较低，我无法解释。或许舍入发生是不精确的
答案 1 :(得分：0)
来自SpriteKit编程指南：
捏造数字 虽然了解Sprite Kit很有用 衡量国际单位制中的项目，令人担忧 准确的数字并不重要。是否是无关紧要的 你的火箭船重量只有1公斤或1,000,000公斤 质量与游戏中使用的其他物理值一致。 通常，比例比实际值更重要 使用
因此质量以千克为单位，脉冲为牛顿秒，扭矩以牛顿为单位，但只要它们在整个游戏中保持一致，它就没那么重要了。