OpenGL：投影鼠标点击几何 [英] OpenGL: projecting mouse click onto geometry

问题描述

我有这个视图集：

  glMatrixMode（GL_MODELVIEW）; //切换到图形透视图
 glLoadIdentity（）; //重新绘制透视图
  

我从鼠标单击中获得一个屏幕位置（sx，sy） 。

给定z的值，如何从sx和sy计算x和y的三维空间？

解决方案

您应该使用 gluUnProject ： 首先，计算对近平面unprojection：

  GLdouble modelMatrix [16]; 
 GLdouble projMatrix [16]; 
 GLint视口[4]; 
 
 glGetIntegerv（GL_VIEWPORT，viewport）; 
 glGetDoublev（GL_MODELVIEW_MATRIX，modelMatrix）; 
 glGetDoublev（GL_PROJECTION_MATRIX，projMatrix）; 
 
 GLdouble x，y，z; 
 gluUnProject（sx，viewport [1] + viewport [3]  -  sy，0，modelMatrix，projMatrix，viewport，& x，& y，& z）; 
  

然后到达远处：

  //将上面的gluUnProject调用替换为
 gluUnProject（sx，viewport [1] + viewport [3]  -  sy，1，modelMatrix，projMatrix，viewport，& x， & y，& z）; 
  

现在，您已经在世界坐标中有一条线，可以找出所有可能的点已被点击。所以现在你只需要插入：假设你得到了z坐标：

  GLfloat nearv [3]，farv [ 3]; //已经如上计算
 
 if（nearv [2] == farv [2]）//这意味着我们没有解决方案
 return; 
 
 GLfloat t =（nearv [2]  -  z）/（nearv [2]  -  farv [2]）; 
 
 //所以这里是所需的（x，y）坐标
 GLfloat x = nearv [0] +（farv [0]  -  nearv [0]）* t，
y = nearv [1] +（farv [1]  -  nearv [1]）* t; 
  

I have this view set:

glMatrixMode(GL_MODELVIEW); //Switch to the drawing perspective
glLoadIdentity(); //Reset the drawing perspective

and I get a screen position (sx, sy) from a mouse click.

Given a value of z, how can I calculate x and y in 3d-space from sx and sy?

解决方案

You should use gluUnProject:

First, compute the "unprojection" to the near plane:

GLdouble modelMatrix[16];
GLdouble projMatrix[16];
GLint viewport[4];

glGetIntegerv(GL_VIEWPORT, viewport);
glGetDoublev(GL_MODELVIEW_MATRIX, modelMatrix);
glGetDoublev(GL_PROJECTION_MATRIX, projMatrix);

GLdouble x, y, z;
gluUnProject(sx, viewport[1] + viewport[3] - sy, 0, modelMatrix, projMatrix, viewport, &x, &y, &z);

and then to the far plane:

// replace the above gluUnProject call with
gluUnProject(sx, viewport[1] + viewport[3] - sy, 1, modelMatrix, projMatrix, viewport, &x, &y, &z);

Now you've got a line in world coordinates that traces out all possible points you could have been clicking on. So now you just need to interpolate: suppose you're given the z-coordinate:

GLfloat nearv[3], farv[3];  // already computed as above

if(nearv[2] == farv[2])     // this means we have no solutions
   return;

GLfloat t = (nearv[2] - z) / (nearv[2] - farv[2]);

// so here are the desired (x, y) coordinates
GLfloat x = nearv[0] + (farv[0] - nearv[0]) * t,
        y = nearv[1] + (farv[1] - nearv[1]) * t;

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