昨天，在关于 iPad 2 新 Garageband 的演示中，Apple 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 平放在桌子上，它应该如何工作。没有运动，没有可测量的加速度，不是吗？
【问题讨论】：
标签： ios iphone ipad uikit accelerometer
一些很好的答案。这是一些工作代码。我将它实现为 UIGestureRecognizer 的子类，以便您可以将其放入并将其附加到 UIView 或 UIButton。一旦触发，它将“压力”设置为 0.0f 和 2.0f 之间的浮点数。您可以选择设置识别所需的最小和最大压力。享受吧。
//
// 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
【讨论】：
我想铝制外壳和桌子不会阻止非常小的运动，而且传感器非常敏感。
或者，如果 iPad 放在 Smart Cover 上，Garage Band 用户体验会更好。
【讨论】：
简单地做这个实验：
使用 XCode 打开 XCode 包中包含的 AccelerometerGraph 教程应用程序。 然后启动应用程序（高通滤波器，最好使用自适应过滤）：您会看到蓝线根据应用程序的强度而变化。当然这会受到表格抖动的影响，这会给测量增加噪音，但您仍然可以通过触摸事件检查加速度计数据来过滤它。
所以这种压力检测使用加速度计是可能的。
【讨论】：
点击区域大小检测？ （用力敲击，指纹更大） 点击动态？
只是想。
【讨论】：
viggio24 是对的。手指区域感应工作正常。 （我在这里有一些帖子用简单的代码行来获取它）。唯一的问题是，如果您启用它，不清楚后果是什么；我们假设它根本不会在最好的情况下获得批准。
【讨论】：
也许是因为陀螺仪更灵敏？结合加速度计数据，即使是微小的运动变化也可能相当容易确定。只是一种预感。除非有什么他们没有告诉我们的，否则这不会是第一次。
【讨论】：
即使 SDK 只向我们公开触摸区域，我相信屏幕硬件也向操作系统提供了更多信息：触摸像素（用于区域检测）和触摸持续时间。它们一起（和试验）可以为您提供对施加压力的良好估计。 如果 Apple 向开发人员发布这种经验压力估计，那就太好了。
【讨论】：
使用 AccelerometerGraph 示例应用自行尝试。设备和桌面的刚度有限，因此您可能会在图中看到一些小光点。
添加：
如果您自己从源代码编译 Apple 的 AccelerometerGraph 图形示例，您可以调高垂直轴上的增益并查看较小加速度的光点。
【讨论】：