【PeterShen_Skysim】Leap Motion 探究【第四篇】-小明编程

这一章说说Coordinate，坐标系。

有朋友要问了，Leap不是本来就有坐标定义吗？对，这里附加的Coordinate是为了更方便的定义实体范围，比如这个官方例子：

红色是Leap硬件能够采集的空间大小，如果我们要让球不能超越一个竖直的界线，我们通常会在程序中设定，超越边界时坐标值保持边界极限值。而Leap给我们提供了一个更加底层一些的做法，自定义坐标系大小，将2D或3D空间自我量化。

倒金字塔是Leap硬件可采集的范围，红色是我们定义出的一个Box，超出这个范围，我们就不要数据了。实例化这个Box即新建一个InteractionBox。这是官方给出的2D平面的坐标量化实例：

int appWidth = 800;
int appHeight = 600;

InteractionBox iBox = leap.Frame().InteractionBox;
Pointable pointable = leap.Frame().Pointables.Frontmost;

Leap.Vector leapPoint = pointable.StabilizedTipPosition;
Leap.Vector normalizedPoint = iBox.NormalizePoint(leapPoint, false);

float appX = normalizedPoint.x * appWidth;
float appY = (1 - normalizedPoint.y) * appHeight;
//The z-coordinate is not used

int appWidth = 800;

int appHeight = 600;

InteractionBox iBox = leap.Frame().InteractionBox;

Pointable pointable = leap.Frame().Pointables.Frontmost;

Leap.Vector leapPoint = pointable.StabilizedTipPosition;

Leap.Vector normalizedPoint = iBox.NormalizePoint(leapPoint, false);

float appX = normalizedPoint.x * appWidth;

float appY = (1 - normalizedPoint.y) * appHeight;

//The z-coordinate is not used

程序指定一个长度800，高度600的垂直剖面。不要疑惑为啥Y轴是(1-y)*Height，因为官方给的例子就是反转的。官方给了一个tip，记得用hand.stabilizedpalmposition或Pointable.stabilizedTipPosition来稳定操作，能有效的过滤掉一些抖动。具体使用，可以借鉴官方的例子：

Leap.Vector differentialNormalizer(Leap.Vector leapPoint,
                           InteractionBox iBox,
                                   bool isLeft,
                                   bool clamp)
{
    Leap.Vector normalized = iBox.NormalizePoint(leapPoint, false);
    float offset = isLeft ? 0.25f : -0.25f;
    normalized.x += offset;

    //clamp after offsetting
    normalized.x = (clamp && normalized.x < 0) ? 0 : normalized.x;
    normalized.x = (clamp && normalized.x > 1) ? 1 : normalized.x;
    normalized.y = (clamp && normalized.y < 0) ? 0 : normalized.y;
    normalized.y = (clamp && normalized.y > 1) ? 1 : normalized.y;

    return normalized;
}

Leap.Vector differentialNormalizer(Leap.Vector leapPoint,

InteractionBox iBox,

bool isLeft,

bool clamp)

{

Leap.Vector normalized = iBox.NormalizePoint(leapPoint, false);

float offset = isLeft ? 0.25f : -0.25f;

normalized.x += offset;

//clamp after offsetting

normalized.x = (clamp && normalized.x < 0) ? 0 : normalized.x;

normalized.x = (clamp && normalized.x > 1) ? 1 : normalized.x;

normalized.y = (clamp && normalized.y < 0) ? 0 : normalized.y;

normalized.y = (clamp && normalized.y > 1) ? 1 : normalized.y;

return normalized;

}

由于定义了坐标系，我们可以调整灵敏度，但通过坐标放大的Scale，灵敏度是线性变化的，这点在大部分情况下适用。官方的例子也给出了：

float appWidth = 800;
float appHeight = 600;

InteractionBox iBox = leap.Frame().InteractionBox;
Pointable pointable = leap.Frame().Pointables.Frontmost;

Leap.Vector leapPoint = pointable.StabilizedTipPosition;
Leap.Vector normalizedPoint = iBox.NormalizePoint(leapPoint, false);

normalizedPoint *= 1.5f; //scale
normalizedPoint -= new Leap.Vector(.25f, .25f, .25f); // re-center

float appX = normalizedPoint.x * appWidth;
float appY = (1 - normalizedPoint.y) * appHeight;
//The z-coordinate is not used

float appWidth = 800;

float appHeight = 600;