我有一个场景，我用openGL渲染几个立方体（程序结构不使用GLUT，它在win32程序结构中，但我只是用glutSolidCube绘制多维数据集）
现在我想通过拾取鼠标来选择这些立方体。这就是我在做的事情：
首先当用户点击场景上的鼠标按钮时，我得到鼠标位置并试图在场景坐标中找到它的坐标（templateSkeletons是我用立方体创建的骨架，仅此而已）：
if (mouse.buttonPressed(Mouse::BUTTON_LEFT))
{
mouse.update();
templateSkeletons[0].selectionMode = true;
Vector3* points;
points = GetOGLPos();
templateSkeletons[0].setIntersectionPoints(points[0],points[1]);
}else
templateSkeletons[0].selectionMode = false;
这是GerOGLPos函数，我正在检索场景中的坐标（注意我有自己的camrea和它自己的投影矩阵，但我只是通过调用{{1}来获取此函数中的投影矩阵这是错的，我应该得到我自己的camrea的投影矩阵？）：
glGetDoublev (GL_PROJECTION_MATRIX, projmatrix);现在我想我有两点表示我在场景中采摘射线。现在，当我渲染立方体时，我尝试计算光线和立方体创建的线的距离，如果它小于值，我改变立方体的颜色以知道我选择它（jointsOfSkeleton指示每个立方体不再创建骨架，在这里我只测试数组中的多维数据集编号6：
Vector3* GetOGLPos()
{Vector3 pointsOnLine[2];
double mvmatrix[16];
double projmatrix[16];
int viewport[4];
double dX, dY, dZ, dClickY,zz;
glGetIntegerv(GL_VIEWPORT, viewport);
glGetDoublev (GL_MODELVIEW_MATRIX, mvmatrix);
glGetDoublev (GL_PROJECTION_MATRIX, projmatrix);
dClickY = double (viewport[3] - mouse.yPos());
// OpenGL renders with (0,0) on bottom, mouse reports with (0,0) on top
//glReadPixels( mouse.xPos(), int(dClickY), 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &zz );
gluUnProject ((double) mouse.xPos(), dClickY, 0.0, mvmatrix, projmatrix, viewport, &dX, &dY, &dZ);
pointsOnLine[0] = Vector3( (float) dX, (float) dY, (float) dZ );
gluUnProject ((double) mouse.xPos(), dClickY, 1.0, mvmatrix, projmatrix, viewport, &dX, &dY, &dZ);
pointsOnLine[1] = Vector3( (float) dX, (float) dY, (float) dZ );
return pointsOnLine;
}
当我点击窗口上不相关的位置时，我看到立方体的颜色变化，它不能正常工作，我正在观察调试器上的距离，距离看起来不正确。这是我用来寻找线点距离的函数：
if(selectionMode)
{
distToLine = Vector3::PointToLineDistance3D(rayPoints[0],rayPoints[1],Vector3::Vector3(jointsOfSkeleton[6].x,
jointsOfSkeleton[6].y,jointsOfSkeleton[6].z));
//distToLine = sqrt(distToLine);
if(distToLine < 0.5)
glColor3f(1.0,0.0,0.0);
else
glColor3f(1.0,1.0,1.0);
}
答案 0 :(得分：2)
这就是我写PointToLineDistance3D：
static float PointToLineDistance3D(const Vector3 &a, const Vector3 &b, const Vector3 &point){
Vector3 lineDirection = Vector3::normalize(b - a), pointDirection = point - a;
float t = Vector3::dot(pointDirection,lineDirection);
Vector3 projection = a + (lineDirection * t);
float ShortestDistance = (projection - point).length();
return ShortestDistance;
}
我假设：
Vector3类有一个length方法，具有明显的含义，*运算符来缩放向量，normalize函数，它返回...一个规范化的向量（这也可以作为避免构造额外对象的方法）。我们的想法是计算point在光线上的投影，然后计算projection和point之间的距离。正如您所看到的，算法与您的实现略有不同，最值得注意的是t的计算。也许这就是你的问题所在。
为了测试我上面提供的代码，我用它编写了一个小程序，它在XY平面上构建了一个3x3的立方体墙，墙的中心是<0,0,0>。即使在移动相机时，我设法让它正常工作。唯一的问题是关于从上到下的鼠标坐标系统（即，Y_鼠标坐标向下增加_），这是自然OpenGL Y轴的对立面。它需要 SDL 库才能编译和运行。
#include <iostream>
#include <GL/gl.h>
#include <GL/glu.h>
#include <SDL/SDL.h>
#include <unistd.h>
#include <Vector3.h>
#define WIDTH 800
#define HEIGHT 600
GLuint box;
int highlight[2]; // position of the cube in the wall
const float cube_width = 5.0;
Vector3 position(0,0,-25); // camera position
// build the cube display list
void setup_cube(){
const float w = cube_width;
float w0 = -w, h0 = -w, w1 = w, h1 = w;
box = glGenLists(1);
glNewList(box, GL_COMPILE);
glBegin(GL_QUAD_STRIP);
glVertex3f(w0, h1, w0);
glVertex3f(w0, h0, w0 );
glVertex3f(w1, h1, w0 );
glVertex3f(w1, h0, w0 );
glVertex3f(w1, h1, w1 );
glVertex3f(w1, h0, w1 );
glVertex3f(w0, h1, w1 );
glVertex3f(w0, h0, w1 );
glEnd();
glBegin(GL_QUAD_STRIP);
glVertex3f(w1, h1, w0 );
glVertex3f(w1, h1, w1 );
glVertex3f(w0, h1, w0 );
glVertex3f(w0, h1, w1 );
glVertex3f(w0, h0, w0 );
glVertex3f(w0, h0, w1 );
glVertex3f(w1, h0, w0 );
glVertex3f(w1, h0, w1 );
glEnd();
glEndList();
}
void setup_scene(){
float r = WIDTH / HEIGHT;
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum( -r, r, -1, 1, 1, 1024);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(position[0],position[1],position[2]);
glEnable(GL_CULL_FACE);
glEnable(GL_DEPTH_TEST);
}
void draw_scene(){
const float w = cube_width;
int i = 0, j = 0;
for (int i = -1; i < 2; i++) {
for (int j = -1; j < 2; j++) {
float x = w * 2 * i, y = w * 2 * j;
if (highlight[0] == i && highlight[1] == j)
glColor3f(0.0, 1.0, 0.0);
else
glColor3f(1.0, 0.0, 0.0);
glPushMatrix ();
glTranslatef(x,y,0);
glCallList(box);
glPopMatrix ();
}
}
}
void aim(float xm, float ym_){
const float w = cube_width;
float ym = HEIGHT - ym_;
GLdouble model[16];
GLdouble proj[16];
GLint view[16];
glGetDoublev(GL_MODELVIEW_MATRIX, model);
glGetDoublev(GL_PROJECTION_MATRIX, proj);
glGetIntegerv(GL_VIEWPORT, view);
highlight[0] = -5;
highlight[1] = -5;
for (int i = -1; i < 2; i++) {
for (int j = -1; j < 2; j++) {
float x = w * 2 * i, y = w * 2 * j;
double ox, oy, oz;
Vector3 centre(x,y,0);
gluUnProject(xm, ym, 0, model, proj, view, &ox, &oy, &oz);
Vector3 p0(ox,oy,oz);
gluUnProject(xm, ym, 1, model, proj, view, &ox, &oy, &oz);
Vector3 p1(ox,oy,oz);
float d = PointToLineDistance(p0,p1,centre);
if (d < w) {
highlight[0] = i;
highlight[1] = j;
return;
}
}
}
}
int main(){
SDL_Surface *screen;
SDL_Init(SDL_INIT_VIDEO);
SDL_GL_SetAttribute( SDL_GL_RED_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_GREEN_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_BLUE_SIZE, 5 );
SDL_GL_SetAttribute( SDL_GL_DEPTH_SIZE, 16 );
SDL_GL_SetAttribute( SDL_GL_DOUBLEBUFFER, 1 );
if ( (screen=SDL_SetVideoMode( WIDTH, HEIGHT, 32, SDL_OPENGL )) == NULL ) {
SDL_Quit();
return -1;
}
setup_cube();
while (1) {
SDL_Event event;
setup_scene();
while(SDL_PollEvent(&event)){
switch(event.type){
case SDL_MOUSEMOTION:
aim(event.motion.x, event.motion.y);
break;
case SDL_KEYDOWN:
{
switch (event.key.keysym.sym){
case SDLK_ESCAPE:
SDL_Quit();
exit(1);
case SDLK_LEFT:
position.add(Vector3(1,0,0));
break;
case SDLK_RIGHT:
position.sub(Vector3(1,0,0));
break;
case SDLK_UP:
position.add(Vector3(0,0,1));
break;
case SDLK_DOWN:
position.sub(Vector3(0,0,1));
break;
case SDLK_PAGEDOWN:
position.add(Vector3(0,1,0));
break;
case SDLK_PAGEUP:
position.sub(Vector3(0,1,0));
break;
}
}
default:
break;
}
}
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
draw_scene();
SDL_GL_SwapBuffers();
usleep(10);
}
return 0;
}
上面列出的源正确显示鼠标指针所针对的立方体。可以使用箭头和向上/向下翻页键来移动。