我正在尝试使用加速度计在圆圈内移动图像.我有一个问题,当图像碰到圆的边缘时,它只是移动圆的另一边.我的代码如下：
- (void)accelerometer:(UIAccelerometer *)accelerometer didAccelerate:(UIAcceleration *)acceleration {
//NSLog(@"x : %g",acceleration.x);
//NSLog(@"y : %g",acceleration.y);
//NSLog(@"z : %g",acceleration.z);
delta.x = acceleration.x * 10;
delta.y = acceleration.y * 10;
joypadCap.center = CGPointMake(joypadCap.center.x + delta.x,joypadCap.center.y - delta.y);
distance = sqrtf(((joypadCap.center.x - 160) * (joypadCap.center.x - 160)) +
((joypadCap.center.y -206) * (joypadCap.center.y - 206)));
//NSLog(@"Distance : %f",distance);
touchAngle = atan2(joypadCap.center.y,joypadCap.center.x);
NSLog(@"Angle : %f",touchAngle);
if (distance > 50) {
joypadCap.center = CGPointMake(160 - cosf(touchAngle) * 50,206 - sinf(touchAngle) * 50);
}
解决方法
尝试使用CMDeviceMotion实现循环水平仪时,我遇到了同样的问题.我发现传递给atan2(y,x)的坐标是一个问题.此功能需要笛卡尔坐标,视图中心有(0,0).但是,屏幕坐标左上角有(0,0).我创建了在两个坐标系之间转换点的方法,现在它运行良好.
我在github上设置了一个示例项目here,但这是最重要的部分：
float distance = sqrtf(((point.x - halfOfWidth) * (point.x - halfOfWidth)) +
((point.y - halfOfWidth) * (point.y - halfOfWidth)));
if (distance > maxDistance)
{
// Convert point from screen coordinate system to cartesian coordinate system,// with (0,0) located in the centre of the view
CGPoint pointInCartesianCoordSystem = [self convertScreenPointToCartesianCoordSystem:point
inFrame:self.view.frame];
// Calculate angle of point in radians from centre of the view
CGFloat angle = atan2(pointInCartesianCoordSystem.y,pointInCartesianCoordSystem.x);
// Get new point on the edge of the circle
point = CGPointMake(cos(angle) * maxDistance,sinf(angle) * maxDistance);
// Convert back to screen coordinate system
point = [self convertCartesianPointToScreenCoordSystem:point inFrame:self.view.frame];
}
和：
- (CGPoint)convertScreenPointToCartesianCoordSystem:(CGPoint)point
inFrame:(CGRect)frame
{
float x = point.x - (frame.size.width / 2.0f);
float y = (point.y - (frame.size.height / 2.0f)) * -1.0f;
return CGPointMake(x,y);
}
- (CGPoint)convertCartesianPointToScreenCoordSystem:(CGPoint)point
inFrame:(CGRect)frame
{
float x = point.x + (frame.size.width / 2.0f);
float y = (point.y * -1.0f) + (frame.size.height / 2.0f);
return CGPointMake(x,y);
}