在 Qt 论坛中，我发现了这个问题并激发了我的好奇心。
我在 Qt 中找到了一个非常简单的示例来显示一个立方体，并修改了立方体逻辑以创建一个边长为 1 个单位的立方体。
然后我尝试点击模型并显示我点击的区域的坐标。
当不涉及旋转时，似乎采摘工作正常。但！如果我取消注释旋转（或其中一个），paintGL我最终会得到“错误”的值。
例如：
- 没有旋转，几乎点击了立方体的最左边的边框：
gluUnProject方法说我点击了点{ -0.49075, 0.234, 0.5 }，这似乎没问题。
- 启用旋转并几乎单击多维数据集的最左侧边框：我收到了 point
{ -0.501456, 0.157555, -0.482942 }，这似乎是错误的。坐标不在其x范围内-0.5, 0.5。
我认为坐标转换是可以的。我一直在通过谷歌进行研究，人们总是使用相同的代码。此外，像素的颜色信息与我点击的面部颜色相匹配。
那么，谁能告诉我为什么当涉及旋转时我得到错误的坐标？我认为我在一些基本的 3D 理解方面失败了，但我无法意识到它在哪里。
这是代码：
主.cpp：
#include <QApplication>
#include "GLCube.h"
int main(int argc, char *argv[])
{
QApplication a(argc, argv);
GLCube w;
w.resize(800,600);
w.show();
return a.exec();
}
GLCube.h
#ifndef GLCUBE_H
#define GLCUBE_H
#include <QtOpenGL>
#include <QGLWidget>
class GLCube : public QGLWidget{
Q_OBJECT // must include this if you use Qt signals/slots
public:
GLCube(QWidget *parent = NULL)
: QGLWidget(parent) {
}
protected:
// Set up the rendering context, define display lists etc.:
void initializeGL();
// draw the scene:
void paintGL();
// setup viewport, projection etc.:
void resizeGL (int width, int height);
virtual void mousePressEvent(QMouseEvent *pme);
};
#endif
GLCube.cpp：
#include "GLCube.h"
#include <cmath>
#include <iostream>
#include <iomanip>
#include "GL/glu.h"
namespace {
float ver[8][3] =
{
{ 0.5, -0.5, 0.5 },
{ -0.5, -0.5, 0.5 },
{ -0.5, -0.5, -0.5 },
{ 0.5, -0.5, -0.5 },
{ 0.5, 0.5, 0.5 },
{ -0.5, 0.5, 0.5 },
{ -0.5, 0.5, -0.5 },
{ +0.5, 0.5, -0.5 }
};
GLfloat color[8][4] =
{
{0.0,0.0,0.0, 1.0},
{1.0,0.0,0.0, 1.0 },
{1.0,1.0,0.0, 1.0 },
{0.0,1.0,0.0, 1.0 },
{0.0,0.0,1.0, 1.0 },
{1.0,0.0,1.0, 1.0 },
{1.0,1.0,1.0, 1.0 },
{0.0,1.0,1.0, 1.0 },
};
void quad(int a,int b,int c,int d, int col)
{
glPointSize( 5 );
glBegin(GL_POINTS);
glColor4fv(color[1]);
glVertex3fv(ver[a]);
glColor4fv(color[2]);
glVertex3fv(ver[b]);
glColor4fv(color[3]);
glVertex3fv(ver[c]);
glColor4fv(color[4]);
glVertex3fv(ver[d]);
glEnd();
glBegin(GL_LINES);
glColor4fv(color[1]);
glVertex3fv(ver[a]);
glVertex3fv(ver[b]);
glColor4fv(color[1]);
glVertex3fv(ver[b]);
glVertex3fv(ver[c]);
glColor4fv(color[1]);
glVertex3fv(ver[c]);
glVertex3fv(ver[d]);
glColor4fv(color[1]);
glVertex3fv(ver[d]);
glVertex3fv(ver[a]);
glEnd();
glBegin(GL_QUADS);
glColor4fv(/*color[a]*/ color[col] );
glVertex3fv(ver[a]);
// glColor3fv(color[b]);
glVertex3fv(ver[b]);
// glColor3fv(color[c]);
glVertex3fv(ver[c]);
// glColor3fv(color[d]);
glVertex3fv(ver[d]);
glEnd();
}
void colorcube()
{
// glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
quad( 3, 2, 1, 0, 1 ); // bottom
quad( 7, 6, 5, 4, 2); // top
quad( 6, 2, 1, 5, 3 ); // front
quad( 7, 3, 0, 4, 5 ); // back
quad( 7, 6, 2, 3, 6 ); // left
quad( 4, 5, 1, 0, 7); // right
}
}
/*
* Sets up the OpenGL rendering context, defines display lists, etc.
* Gets called once before the first time resizeGL() or paintGL() is called.
*/
void GLCube::initializeGL(){
//activate the depth buffer
glEnable(GL_DEPTH_TEST);
qglClearColor(Qt::black);
glEnable(GL_CULL_FACE);
}
/*
* Sets up the OpenGL viewport, projection, etc. Gets called whenever the widget has been resized
* (and also when it is shown for the first time because all newly created widgets get a resize event automatically).
*/
void GLCube::resizeGL (int width, int height){
glViewport( 0, 0, (GLint)width, (GLint)height );
/* create viewing cone with near and far clipping planes */
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glFrustum( -1.0, 1.0, -1.0, 1.0, 15.0, 30.0);
glMatrixMode( GL_MODELVIEW );
}
/*
* Renders the OpenGL scene. Gets called whenever the widget needs to be updated.
*/
void GLCube::paintGL(){
//delete color and depth buffer
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0f,0.0f,-20.0f); //move along z-axis
glRotatef(30.0,0.0,1.0,0.0); //rotate 30 degress around y-axis
glRotatef(15.0,1.0,0.0,0.0); //rotate 15 degress around x-axis
colorcube();
// originalcube();
}
void GLCube::mousePressEvent(QMouseEvent *pme) {
GLint viewport[4];
GLdouble modelview[16];
GLdouble projection[16];
glGetDoublev( GL_MODELVIEW_MATRIX, modelview );
glGetDoublev( GL_PROJECTION_MATRIX, projection );
glGetIntegerv( GL_VIEWPORT, viewport );
const int x = pme->x();
const int y = viewport[3] - pme->y();
qDebug() << "HERE: " << x << y;
GLfloat color[4];
glReadPixels( x, y, 1, 1, GL_RGBA, GL_FLOAT, color);
GLenum error = glGetError();
std::cout << "RETRIEVED COLOR:" << color[0] << ", " << color[1] << ", " << color[2] << ", " << color[3] << std::endl;
printf( "\tERROR: %s (Code: %u)\n", gluErrorString(error), error );
if(GL_NO_ERROR != error) throw;
GLdouble depthScale;
glGetDoublev( GL_DEPTH_SCALE, &depthScale );
std::cout << "DEPTH SCALE: " << depthScale << std::endl;
GLfloat z;
glReadPixels( x, y, 1, 1, GL_DEPTH_COMPONENT, GL_FLOAT, &z );
error = glGetError();
std::cout << "X: " << x << ", Y: " << y << ", RETRIEVED Z: " << z << std::endl;
printf( "\tERROR: %s (Code: %u)\n", gluErrorString(error), error );
if(GL_NO_ERROR != error) throw;
std::cout << std::endl << std::endl;
GLdouble posX, posY, posZ;
GLint result;
result = gluUnProject( x, y, z, modelview, projection, viewport, &posX, &posY, &posZ);
error = glGetError();
std::cout << "3D point with POS: " << posX << " " << posY << " " << posZ << std::endl;
printf( "\tERROR: %s (Code: %u)\n", gluErrorString(error), error );
std::cout << "\tglUnProject: " << (( GL_FALSE == result ) ? "FALSE" : "TRUE") << std::endl;
if(GL_NO_ERROR != error) throw;
}
笔记：
我在 Windows 8.1 64 位、Qt 4.8 和 MinGW 中运行它。
此外，两者都没有错误glReadPixels地gluUnProject退出（错误代码= GL_NO_ERROR）
并且glut不可用。只有什么OpenGL，QtOpenGL和/或glu提供。