使用加速度计的敲击压力强度检测

Question

昨天，在关于iPad 2新款Garageband的演示中，苹果公司演示了一个有趣的功能：使用加速度计检测敲击压力。 （请参阅Garageband page上的鼓部分。）

我想知道如果iPad在桌子上平放，应该如何工作。没有运动，没有可测量的加速度，不是？

Answer 1

一些很好的答案。这是一些工作代码。我将它作为UIGestureRecognizer的子类实现，以便您可以将它放入并附加到UIView或UIButton。一旦触发，它将“压力”设置为0.0f和2.0f之间的浮动。您可以选择设置识别所需的最小和最大压力。请享用。

// 
// CPBPressureTouchGestureRecognizer.h 
// PressureSensitiveButton 
// 
// Created by Anthony Picciano on 3/21/11. 
// Copyright 2011 Anthony Picciano. All rights reserved. 
// 
// Redistribution and use in source and binary forms, with or without 
// modification, are permitted provided that the following conditions 
// are met: 
// 1. Redistributions of source code must retain the above copyright 
//  notice, this list of conditions and the following disclaimer. 
// 2. Redistributions in binary form must reproduce the above copyright 
//  notice, this list of conditions and the following disclaimer in the 
//  documentation and/or other materials provided with the distribution. 
// 
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 
// OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 
// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
// NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 
// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
// 

#import <UIKit/UIKit.h> 

#define CPBPressureNone   0.0f 
#define CPBPressureLight  0.1f 
#define CPBPressureMedium  0.3f 
#define CPBPressureHard   0.8f 
#define CPBPressureInfinite  2.0f 

@interface CPBPressureTouchGestureRecognizer : UIGestureRecognizer <UIAccelerometerDelegate> { 
    @public 
    float pressure; 
    float minimumPressureRequired; 
    float maximumPressureRequired; 

    @private 
    float pressureValues[30]; 
    uint currentPressureValueIndex; 
    uint setNextPressureValue; 
} 

@property (readonly, assign) float pressure; 
@property (readwrite, assign) float minimumPressureRequired; 
@property (readwrite, assign) float maximumPressureRequired; 

@end 


// 
// CPBPressureTouchGestureRecognizer.h 
// PressureSensitiveButton 
// 
// Created by Anthony Picciano on 3/21/11. 
// Copyright 2011 Anthony Picciano. All rights reserved. 
// 
// Redistribution and use in source and binary forms, with or without 
// modification, are permitted provided that the following conditions 
// are met: 
// 1. Redistributions of source code must retain the above copyright 
//  notice, this list of conditions and the following disclaimer. 
// 2. Redistributions in binary form must reproduce the above copyright 
//  notice, this list of conditions and the following disclaimer in the 
//  documentation and/or other materials provided with the distribution. 
// 
// THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR 
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES 
// OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. 
// IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, 
// INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT 
// NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 
// DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 
// (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF 
// THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
// 

#import <UIKit/UIGestureRecognizerSubclass.h> 
#import "CPBPressureTouchGestureRecognizer.h" 

#define kUpdateFrequency   60.0f 
#define KNumberOfPressureSamples 3 

@interface CPBPressureTouchGestureRecognizer (private) 
- (void)setup; 
@end 

@implementation CPBPressureTouchGestureRecognizer 
@synthesize pressure, minimumPressureRequired, maximumPressureRequired; 

- (id)initWithTarget:(id)target action:(SEL)action { 
    self = [super initWithTarget:target action:action]; 
    if (self != nil) { 
     [self setup]; 
    } 
    return self; 
} 

- (id)init { 
    self = [super init]; 
    if (self != nil) { 
     [self setup]; 
    } 
    return self; 
} 

- (void)setup { 
    minimumPressureRequired = CPBPressureNone; 
    maximumPressureRequired = CPBPressureInfinite; 
    pressure = CPBPressureNone; 

    [[UIAccelerometer sharedAccelerometer] setUpdateInterval:1.0f/kUpdateFrequency]; 
    [[UIAccelerometer sharedAccelerometer] setDelegate:self]; 
} 

#pragma - 
#pragma UIAccelerometerDelegate methods 

-(void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration { 
    int sz = (sizeof pressureValues)/(sizeof pressureValues[0]); 

    // set current pressure value 
    pressureValues[currentPressureValueIndex%sz] = acceleration.z; 

    if (setNextPressureValue > 0) { 

     // calculate average pressure 
     float total = 0.0f; 
     for (int loop=0; loop<sz; loop++) total += pressureValues[loop]; 
     float average = total/sz; 

     // start with most recent past pressure sample 
     if (setNextPressureValue == KNumberOfPressureSamples) { 
      float mostRecent = pressureValues[(currentPressureValueIndex-1)%sz]; 
      pressure = fabsf(average - mostRecent); 
     } 

     // caluculate pressure as difference between average and current acceleration 
     float diff = fabsf(average - acceleration.z); 
     if (pressure < diff) pressure = diff; 
     setNextPressureValue--; 

     if (setNextPressureValue == 0) { 
      if (pressure >= minimumPressureRequired && pressure <= maximumPressureRequired) 
       self.state = UIGestureRecognizerStateRecognized; 
      else 
       self.state = UIGestureRecognizerStateFailed; 
     } 
    } 

    currentPressureValueIndex++; 
} 

#pragma - 
#pragma UIGestureRecognizer subclass methods 

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event { 
    setNextPressureValue = KNumberOfPressureSamples; 
    self.state = UIGestureRecognizerStatePossible; 
} 

- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event { 
    self.state = UIGestureRecognizerStateFailed; 
} 

- (void)reset { 
    pressure = CPBPressureNone; 
    setNextPressureValue = 0; 
    currentPressureValueIndex = 0; 
} 

@end 

Answer 2

点击面积大小检测？ （较硬的水龙头，较大的指纹） 水龙头动态？

只是在想。

Answer 3

也许是由于比较敏感陀螺仪？结合加速度计数据，确定运动的微小变化可能相当容易。只是一种预感。除非他们没有告诉我们什么，这不会是第一个。

Answer 4

我想象，铝制外壳和桌子不会阻止非常小的移动，并且传感器非常敏感。

或者，Garage Band的用户体验对于iPad站在智能封面上更好。

Answer 5

即使SDK暴露给我们的触摸区域，我相信屏幕硬件正在向操作系统提供更多信息：触摸像素（用于区域检测）和触摸持续时间。一起（和试验）他们可以给你一个很好的施加压力的估计。 如果苹果向开发者发布这种经验性的压力估计，那将会很好。

Answer 6

自己动手尝试使用AccelerometerGraph示例应用程序。该设备和桌面具有有限的硬度，因此您可能会在图表中看到小点。

新增：

如果您编译从自己的源代码苹果AccelerometerGraph图示例，您可以打开了在垂直轴上增益和看到的光点较小的加速度。

Answer 7

那么简单地做这个实验：

与XCode的包括在Xcode捆绑的AccelerometerGraph教程应用程序打开。 然后启动应用程序（高通滤波器，使用自适应滤波效果更好）：您将看到根据应用程序强度改变的蓝线。当然，这受到表格抖动的影响，这会给测量增加噪音，但您仍然可以通过检查加速度计数据和触摸事件来对其进行过滤。

所以这种压力检测可以使用加速度计。

Answer 8

viggio24是对的。手指区域感应正常工作。 （我在这里有一些简单的代码行来获取它）。唯一的问题是，如果您启用它后会产生什么后果？我们认为它不会在最好的情况下获得批准。