我正在尝试获得一些 OpenGL 的实践经验,所以我一直在编写一些基本程序。下面的简短程序是我第一次尝试渲染一个实体对象——一个旋转的立方体——但由于某种原因,一些后多边形似乎被绘制在前多边形上。我的问题是什么可能导致这种情况?它与深度缓冲区有关吗?我发现在这种情况下启用面部剔除会隐藏效果,但为什么需要这样做呢?不应该隐藏被更近的脸遮挡的脸吗?
#include <GL/gl.h>
#include <GL/glu.h>
#include <GL/glut.h>
typedef struct{
int width;
int height;
char * title;
} window;
window win;
float theta = 0;
const float rotRate = 0.05;//complete rotations per second
int lastTime;
const float verts[][3] = {
{0.0,0.0,0.0},
{1.0,0.0,0.0},
{0.0,1.0,0.0},
{0.0,0.0,1.0},
{0.0,1.0,1.0},
{1.0,0.0,1.0},
{1.0,1.0,0.0},
{1.0,1.0,1.0}};
const int faceIndices[][4] = {
{3,5,7,4},//front
{1,0,2,6},//back
{4,7,6,2},//top
{0,1,5,3},//bottom
{5,1,6,7},//right
{0,3,4,2}};//left
void display(){
//timing and rotation
int currentTime = glutGet(GLUT_ELAPSED_TIME);
int dt = lastTime - currentTime;
lastTime = currentTime;
theta += (float)dt/1000.0*rotRate*360.0;
if (theta > 360.0) theta += -360.0;
//draw
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0.0, 0.0, -5.0);
glRotatef(theta, 0.0, 1.0, 0.0);
glTranslatef(-1.0,-1.0,-1.0);
glScalef(2.0, 2.0, 2.0);
int f;
for(f=0; f<6;f++){
glBegin(GL_POLYGON);
int v;
for(v=0; v<4; v++){
glColor3fv(verts[faceIndices[f][v]]);
glVertex3fv(verts[faceIndices[f][v]]);
}
glEnd();
}
glutSwapBuffers();
}
void initializeGLUT(int * argc, char ** argv){
glutInit(argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_DEPTH | GLUT_DOUBLE);
glutInitWindowSize(win.width, win.height);
glutCreateWindow("OpenGL Cube");
glutDisplayFunc(display);
glutIdleFunc(display);
}
void initializeGL(){
//Setup Viewport matrix
glViewport(0,0,win.width, win.height);
//Setup Projection matrix
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45,(float) win.width/win.height, 0.1, 100.0);
//Initialize Modelview matrix
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
//Other
glClearColor(0.0, 0.0, 0.0, 0.0);
glClearDepth(1.0);
}
int main(int argc, char** argv){
win.width = 640;
win.height = 480;
initializeGLUT(&argc, argv);
initializeGL();
glutMainLoop();
return 0;
}