按照RedBook中的代码在OpenGL中绘制二十面体时缺少面孔 [英] Faces missing when drawing icosahedron in OpenGL following code in redBook
问题描述
我正在尝试在此流行的OpenGl教程中绘制二十面体红皮书.
I am attempting to draw an icosahedron following this popular OpenGl tutorial in the redBook.
我正在使用GLUT处理窗口.
I am using GLUT to handle windowing.
这是我完整的代码.它主要是本教程中的代码以及使用GLUT进行的一些文书工作
Here is my complete code. It is mostly the code from the tutorial plus some clerical work using GLUT
#include <stdio.h>
#include <GL/glut.h>
#define X .525731112119133606
#define Z .850650808352039932
void mouseEventHandler(int button, int state, int x, int y){
}
void display() {
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
static GLfloat vdata[12][3] = {
{-X,0.0,Z}, {X,0.0,Z}, {-X,0.0,-Z}, {X,0.0,-Z},
{0.0,Z,X}, {0.0,Z,-X}, {0.0,-Z,X}, {0.0,-Z,-X},
{Z,X,0.0}, {-Z,X,0.0}, {Z,-X,0.0}, {-Z,-X,0.0},
};
static GLuint tindices[20][3] = {
{0,4,1}, {0,9,4}, {9,5,4}, {4,5,8}, {4,8,1},
{8,10,1}, {8,3,10}, {5,3,8}, {5,2,3}, {2,7,3},
{7,10,3}, {7,6,10}, {7,11,6}, {11,0,6}, {0,1,6},
{6,1,10}, {9,0,11}, {9,11,2}, {9,2,5}, {7,2,11} };
int i;
glBegin(GL_TRIANGLES);
for (i = 0; i < 20; i++){
glNormal3fv(&vdata[tindices[i][0]][0]);
glVertex3fv(&vdata[tindices[i][0]][0]);
glNormal3fv(&vdata[tindices[i][1]][0]);
glVertex3fv(&vdata[tindices[i][1]][0]);
glNormal3fv(&vdata[tindices[i][2]][0]);
glVertex3fv(&vdata[tindices[i][2]][0]);
}
glEnd();
glFlush ( );
}
void windowSetup(){
glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
glutInitWindowPosition(80, 80);
glutInitWindowSize(1000,1000);
glutCreateWindow("OpenGL Ico");
glClear(GL_COLOR_BUFFER_BIT);
glMatrixMode( GL_MODELVIEW);
glLoadIdentity();
gluOrtho2D( -2.0, 2.0, -2.0, 2.0 );
}
int main(int argc, char** argv) {
glutInit(&argc, argv);
windowSetup();
glutDisplayFunc(display);
glutMouseFunc(&mouseEventHandler);
glutMainLoop();
}
这是我的输出:
这与预期的输出有很大不同:
This is my output:
This is very different from the expected output:
有人知道为什么这些差异如此大吗?
Does someone know why these differ so much?
差异似乎是:
-
我的二十面体缺少面孔
My icosahedron is missing faces
我的二十面体正以不同的角度观看
My icosahedron is being viewed from a different angle
我的二十面体的照明方式不同
My icosahedron is lit differently
第一个是最紧迫的.我已经注意到，当我将glMatrixMode( GL_MODELVIEW);更改为glMatrixMode( GL_PROJECTION);时，没有出现的面孔会出现，而当前出现的面孔会消失.有人知道为什么会这样吗?
The first one is the most pressing. I have noticed when I change glMatrixMode( GL_MODELVIEW); to glMatrixMode( GL_PROJECTION); the faces that aren't showing up appear and those that are currenty appearing disappear. Does anybody know why this could be?
推荐答案
-
缺少面孔
很可能您只是索引顺序错误.在这种情况下，将它们反向可以解决问题.要检查这一点，您可以尝试:
most likely you just have wrong order of indices. In such case Reversing them will solve the issue. To check this you can try:
glDisable(GL_CULL_FACE);
如果问题消失，我是对的.如果不是这样的话，那就不一样了(比如太接近Z_NEAR的镜头切割，但是看起来会有些不同).
if problem disappears I am right. If not it is different thing (like too close to camera cutting by Z_NEAR but that would look a bit different).
要确定正确的面孔，您可以使用基于i的glColor作为示例
To identify the correct face you can use glColor based on i for exaple
if (i==5) glColor3f(1.0,0.0,0.0); else glColor3f(1.0,1.0,1.0);
在这种情况下，红脸将是第六个{8,3,10}
the red face would be the 6th in this case {8,3,10}
照明
您将顶点坐标用作法线，因此不要期望 FLAT 阴影.另外，我看不到您在此处设置任何灯光(但可以将其隐藏在我不使用的 GLUT 中).为了解决这个问题，每个三角形仅使用一个法线即可.因此，平均得到的3个法线，并从中得出一个单位向量并使用该向量(在每个三角形的第一个glVertex调用之前).
You are using vertex coordinates as normals so do not expect FLAT shading. Also I do not see you are setting any lights here (but that can be hidden in GLUT somewhere I do not use it). To remedy this use just single normal per triangle. so average the 3 normals you got and make an unit vector from that and use that (before first glVertex call of each triangle).
方向
只需将GL_MODELVIEW旋转到所需方向即可.标准透视图GL_PROJECTION具有z轴作为查看方向，并且x,y轴与屏幕匹配(GL_MODELVIEW为单位)
just rotate your GL_MODELVIEW to desired orientation. Standard perspective GL_PROJECTION has z axis as viewing direction and x,y axises matches the screen (while GL_MODELVIEW is unit)
[Edit1]我尝试了您的代码
所以问题是，您得到了相反的索引顺序，然后在OpenGL中(至少在我的环境中)使用了默认的多边形缠绕，并且这里的法线错误固定了代码:
So the problem is you got reverse order of indices then default polygon winding in OpenGL (at least in my environment) and wrong normals here fixed code:
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
const GLfloat vdata[12][3] =
{
{-X,0.0,Z}, {X,0.0,Z}, {-X,0.0,-Z}, {X,0.0,-Z},
{0.0,Z,X}, {0.0,Z,-X}, {0.0,-Z,X}, {0.0,-Z,-X},
{Z,X,0.0}, {-Z,X,0.0}, {Z,-X,0.0}, {-Z,-X,0.0},
};
const GLuint tindices[20][3] =
{
{0,4,1}, {0,9,4}, {9,5,4}, {4,5,8}, {4,8,1},
{8,10,1}, {8,3,10}, {5,3,8}, {5,2,3}, {2,7,3},
{7,10,3}, {7,6,10}, {7,11,6}, {11,0,6}, {0,1,6},
{6,1,10}, {9,0,11}, {9,11,2}, {9,2,5}, {7,2,11}
};
int i;
GLfloat nx,ny,nz;
glEnable(GL_CULL_FACE);
glFrontFace(GL_CW);
glBegin(GL_TRIANGLES);
for (i = 0; i < 20; i++)
{
nx =vdata[tindices[i][0]][0];
ny =vdata[tindices[i][0]][1];
nz =vdata[tindices[i][0]][2];
nx+=vdata[tindices[i][1]][0];
ny+=vdata[tindices[i][1]][1];
nz+=vdata[tindices[i][1]][2];
nx+=vdata[tindices[i][2]][0]; nx/=3.0;
ny+=vdata[tindices[i][2]][1]; ny/=3.0;
nz+=vdata[tindices[i][2]][2]; nz/=3.0;
glNormal3f(nx,ny,nz);
glVertex3fv(vdata[tindices[i][0]]);
glVertex3fv(vdata[tindices[i][1]]);
glVertex3fv(vdata[tindices[i][2]]);
}
glEnd();
预览:
这是屏幕截图，并且我的对象正在旋转，所以不要期望您期望的正确方向.
it is a screenshot and my object is rotating so do not expect correct orientation you expect.
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