检查一个脸向上/向下朝鼠标方向 [英] Check a face is upwards/downwards towards mouse direction

问题描述

假设我有一个在三维空间中，该摄像头转身通过用户交互单个面。当鼠标光标击中脸，一个光线投射检测的交叉点。没什么特别的这么远。<​​/ P>

问：如何检测，如果相机看脸的下跌或上涨

我有鼠标的方向向量和正常的脸，以及。什么是在three.js的操作（或数学，如果你想）。

解决方案

您需要做你的脸，正常和你的相机前向向量之间的点积。

如果该产品是正它背离相机，如果它是负的它的面对摄像机

伪code：

 如果（点（camera.forward，face.normal）℃下）
    //所面临的相机
其他
    //背离相机
 

Assume I a have a single face in 3D space, which the camera turns around by user interaction. When the mouse cursor hits the face, a raycast detects the intersection. Nothing special so far.

Question: How to detect if the camera looks at the downside or upside of the face?

I do have the mouse direction vector and the faces normal as well. What would be the operation in three.js (or mathematically if you want).

解决方案

You need to do a dot product between your face normal and your camera forward vector.

If the product is positive it's facing away from the camera, if it's negative it's facing the camera.

pseudocode:

if (dot(camera.forward, face.normal) < 0)
    // facing the camera
else
    // facing away from the camera

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