如何在旋转对象时在OpenGL中固定光源? [英] How do I fixate a light source in OpenGL while rotating an object?

问题描述

我有一个glutSolidTeapot(其表面法线根据opengl.org自动生成)和一个发出散射光的光源.当我尝试旋转茶壶时，问题就来了:似乎光源也在旋转，而不是保持在我定义的相同位置(本质上是跟随茶壶).如您在我的代码中看到的那样，我仅在初始化时修改照明位置，因此它不会受到glRotatef()的影响，因为它在设置照明位置后称为 .

I have a glutSolidTeapot (which has its surface normals generated automatically according to opengl.org) and a light source which is emitting diffuse light. The problem comes when I try to rotate the teapot: it seems like the light source is doing the rotation as well, not remaining in the same position I defined it (it essentially follows the teaspot). As you can see in my code, I only modify the lighting position upon initialization, so it is not subjected to glRotatef(), since its called after setting the light position.

尽管花了很多时间来解决这个问题，但我真的不知道这种行为可以归因于什么.

Despite spending numerous hours trying to solve this problem, I really have no idea what this kind of behavior can be attributed to.

粘贴glEnable(GL_NORMALIZE);初始化也不能解决问题.

Pasting glEnable(GL_NORMALIZE); in the initialization does not solve the problem neither.

我认为所需的输出应该是一个右侧有光泽的茶壶(因为光线来自该方向)，无论茶壶旋转了什么角度.

I think the desired output should be a teapot with a shiny right side (since the light is coming from that direction), no matter what angle the teapot is rotated by.

如果要测试我的代码，请按Space键旋转茶壶.

If you want to test my code, press Space to rotate the teapot.

#include <math.h>
#include <stdlib.h>

#if defined(WIN32) || defined(_WIN32) || defined(__WIN32__)
#include <windows.h>     
#endif

#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>     

void onInitialization( ) { //creating the light source
 glEnable(GL_LIGHTING);
 glEnable(GL_DEPTH_TEST); 

 GLfloat diffuse[]={0.8, 0.8, 0.8, 1.0};
 GLfloat pos[]={0.5, 0.0, 0.8, 0.0};

 glLightfv(GL_LIGHT0, GL_DIFFUSE, diffuse);
 glLightfv(GL_LIGHT0, GL_POSITION, pos);

 glEnable(GL_LIGHT0);

 glRotatef(-90, 1, 0, 0); //we want to see the top of the teapot
}

void onDisplay( ) {
    glClearColor(0.1f, 0.2f, 0.3f, 1.0f);
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);

 //rotating on every frame (for testing purposes only)
 glRotatef(5, 0,1,0);
 glutSolidTeapot(0.4);

    glFinish();
    glutSwapBuffers();
}


void onKeyboard(unsigned char key, int x, int y) {
 if (key==32){ //do rotation upon hitting the Space key
  glutPostRedisplay();
 }
}

int main(int argc, char **argv) {
    glutInit(&argc, argv); 
    glutInitWindowSize(600, 600);
    glutInitWindowPosition(100, 100);
    glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE | GLUT_DEPTH);
    glutCreateWindow("Teapot");

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    onInitialization();

    glutDisplayFunc(onDisplay);
    glutKeyboardFunc(onKeyboard);

    glutMainLoop();

    return 0;
}

推荐答案

我认为正在改变

glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glMatrixMode(GL_PROJECTION);
glLoadIdentity();

到

glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();

是一个很好的起点.

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