ARCore中根据屏幕坐标计算射线的算法

 1 class Ray {
 2 
 3     public final Vector3f origin;//射线起点
 4     public final Vector3f direction;//射线方向
 5 
 6     public Ray(Vector3f origin, Vector3f direction) {
 7         this.origin = origin;
 8         this.direction = direction;
 9     }
10 
11     //根据屏幕坐标计算射线——3D拾取
12     public static Ray screenPointToRay(Vector2f point, Vector2f viewportSize, float[] viewProjMtx) {
13         point.y = viewportSize.y - point.y;//转化为左下角为原点
14         float x = point.x * 2.0F / viewportSize.x - 1.0F;//转换到[-1,1]
15         float y = point.y * 2.0F / viewportSize.y - 1.0F;//转换到[-1,1]
16 
17         float[] farScreenPoint = new float[]{x, y, 1.0F, 1.0F};//远平面上的坐标透视除法之后的值
18         float[] nearScreenPoint = new float[]{x, y, -1.0F, 1.0F};//近平面上的坐标透视除法之后的值
19 
20         float[] nearPlanePoint = new float[4];//用于记录世界坐标系下，近平面上的点
21         float[] farPlanePoint = new float[4];//用于记录世界坐标系下，远平面上的点
22 
23         float[] invertedProjectionMatrix = new float[16];
24         Matrix.setIdentityM(invertedProjectionMatrix, 0);
25         Matrix.invertM(invertedProjectionMatrix, 0, viewProjMtx, 0);//计算逆矩阵
26 
27         Matrix.multiplyMV(nearPlanePoint, 0, invertedProjectionMatrix, 0, nearScreenPoint, 0);//计算世界坐标系中，对应到近平面的坐标
28         Matrix.multiplyMV(farPlanePoint, 0, invertedProjectionMatrix, 0, farScreenPoint, 0);
29 
30         Vector3f direction = new Vector3f(farPlanePoint[0] / farPlanePoint[3], farPlanePoint[1] / farPlanePoint[3], farPlanePoint[2] / farPlanePoint[3]);
31         Vector3f origin = new Vector3f(new Vector3f(nearPlanePoint[0] / nearPlanePoint[3], nearPlanePoint[1] / nearPlanePoint[3], nearPlanePoint[2] / nearPlanePoint[3]));
32         direction.sub(origin);
33         direction.normalize();
34         return new Ray(origin, direction);
35     }   
36 }