c - GluProject 未在 C 中显示准确的坐标

Question

我正在尝试从 opengl 坐标(投影在 3D 空间中)找到屏幕坐标，为此我使用了 glproject 调用，我在代码中使用了旋转和平移

在执行一些转换后的某个时刻，我调用 glproject api 来获取特定投影点 P(x,y,z) 的屏幕坐标

glproject(x,y,z,模型矩阵,投影矩阵,视口(viewport),*x_s,*y_s,*z_s);

我能够在 x_s 中正确获取 x 屏幕坐标，但 y 坐标不同

y 中唯一的变化(x 中没有)是当我最初调用 glperspective 来设置 fovy(视野角，以度为单位，在 y 方向)时。 gluPerspective(60.0f, 宽度/高度,0.0001f,1000.0f);

让我重新表述一下这个问题:我在屏幕上创建了一个 3D 点，现在我通过 GLproject 获取该点的 2d(x,y) 坐标，它们与鼠标坐标不同。获得正确的可能解决方案是什么坐标。

这是代码片段

#include<GL/glut.h>     /* Header File For The GLUT Library */
GLint Window;              /* The number of our GLUT window */
float tmp_x,tmp_y,tmp_z;
GLfloat w = 1200;         /* Window size. Global for use in rotation routine */
GLfloat h = 1200;
GLint prevx, prevy;        /* Remember previous x and y positions */
GLfloat xt=1.0,yt=1.0,zt=1.0;   /* translate */
int width = 1600;
int height = 1200;

//This function will set windowing transformation
void transform(GLfloat Width , GLfloat Height )
{
    glViewport(0,0,  (GLfloat)Width,  (GLfloat)Height);
    glPushMatrix();
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(60.0f, Width/Height,0.0001f,1000.0f); 
    glTranslatef(0.0, 0.0, -15.0f);     /* Centre and away the viewer */
    glMatrixMode(GL_MODELVIEW);
    glPopMatrix();
}


GLvoid draw_room() 
{   
int i;
glPushMatrix();
glShadeModel(GL_SMOOTH); 
glLineWidth(1.0);                             
glPointSize(4.0);                             /* Add point size, to make it clear */
glBegin(GL_POINTS);                /* start drawing the cube.*/
glColor3f(0.0f,0.0f,1.0f);            /* Set The Color To Orange*/
glColor3f(1.0f,0.0f,0.0f);            /* Set The Color To Orange*/
glVertex3f(3.1f,2.1f,2.1f); 
glEnd();                              /* Done Drawing The Cube*/
glEnable(GL_DEPTH_TEST); 
}
//OpenGl Display  callback Function It call init room
void DrawGLScene()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT); 
    printf("%f %f %f\n",xt,yt,zt);
    glPushMatrix();
    glMatrixMode(GL_PROJECTION);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(xt,yt, zt);
    draw_room();
    glPopMatrix();
    glutSwapBuffers();               /* Swap buffers */
    glFlush();
}

GLvoid Mouse( int b , int s, int xx, int yy)
{

    double a1,a2,a3;    
    GLint viewport[4];
    GLdouble modelview[16];
    GLdouble projection[16]; 
    glGetIntegerv(GL_VIEWPORT, viewport);  
    glGetDoublev(GL_MODELVIEW_MATRIX, modelview);   
    glGetDoublev(GL_PROJECTION_MATRIX, projection);  
    //gluProject(xt+3.1f,yt+2.1f,zt+2.1f, modelview, projection, viewport, &a1, &a2, &a3);
    gluProject(3.1f,2.1f,2.1f, modelview, projection, viewport, &a1, &a2, &a3);

    printf("Mouse: %d %d\n",xx,yy);                // Both Print are giving different coordinaes.
    printf("Unproject %f %f %f\n",a1,a2,a3);    
    switch (b) {
    case GLUT_LEFT_BUTTON:  /* only stash away for left mouse */
        prevx = xx - w/2;
        prevy = h/2 - yy;
        break;
    case GLUT_MIDDLE_BUTTON:
        break;
    case GLUT_RIGHT_BUTTON:
        break;
    }
}

可能的解决方案是什么？

Answer 1

OpenGL使用屏幕左下角作为坐标系原点。窗口系统通常使用左上角作为坐标系原点。您需要处理这种差异。示例:

printf("Mouse: %d %d\n",xx,yy);                
printf("Unproject %f %f %f\n",a1,viewport[1]-a2,a3);