OpenGL代码

Question

我的理解是当我试图访问尚未考虑的内存时发生分段错误。我似乎无法找到错误。我已经测试了在此代码之外填充数组的过程并且它工作正常，我认为错误必须在我分配的可用空间中，但我已经分配了5倍的内存，但仍然会出现分段错误，所以我对这个很不确定。

 #include <cmath>
    #include <iostream>

    #ifdef __APPLE__
#  include <GL/glew.h>
#  include <GL/freeglut.h>
#  include <OpenGL/glext.h>
#else
#  include <GL/glew.h>
#  include <GL/freeglut.h>
#  include <GL/glext.h>
#pragma comment(lib, "glew32.lib") // Compiler directive to include the GLEW library.
#endif

#define PI 3.14159265



using namespace std;
/*we have to draw a circular lampshade... USING VERTEX ARRs*/
static float R1 = 10.0;
static float R2 = 8.0;
static float h = 10;
static float H = 10;
static float Xangle = 0.0, Yangle = 0.0, Zangle = 0.0; // Angles to
static int p = 6; // number of subdiviions of 2 * PI
static float *verts = NULL;
static unsigned int *inds = NULL;
//there are 2*(p+1) vertices
//but verts has size, 6*(p+1)
void fillVer(void)
{
    int i,j;
    i = -1;
    for(j = 0; j <= p; j++)
    {
    verts[i++] = R1 * cos(2.0 * PI * (j/p));
        verts[i++] = R1 * sin(2.0 * PI * (j/p));
        verts[i++] = h;
    }
    for(j = 0; j <= p; j++)
    {
    verts[i++] = R2 * cos(2.0 * PI * (j/p));
        verts[i++] = R2 * sin(2.0 * PI * (j/p));
        verts[i++] = H;
    }
}
// there are 2*(p+1) vertices
void fillInd(void)
{
int j = 0;
   for(int i = 0; i <= p; i++)
   {
       inds[j] = i;
       inds[j++] = i+(p+1);
   }
}

void setup(void)
{
    glClearColor(1.0, 1.0, 1.0, 0.0);
    glEnableClientState(GL_VERTEX_ARRAY);
}

void drawScene(void)
{
    glClear(GL_COLOR_BUFFER_BIT);
    glLoadIdentity();
    glColor3f(0,0,0);
    verts = new float[6*(p + 1)];
    inds = new unsigned int[2*(p+1)];
    fillVer();
    fillInd();
    glVertexPointer(3,GL_FLOAT,0,verts);
    glTranslatef(0.0, 0.0, -10.0);
    glRotatef(Zangle, 0.0, 0.0, 1.0);
    glRotatef(Yangle, 0.0, 1.0, 0.0);
    glRotatef(Xangle, 1.0, 0.0, 0.0);
    glPolygonMode(GL_FRONT_AND_BACK,GL_LINE);
    glDrawElements(GL_TRIANGLE_STRIP,2*(p+1),GL_UNSIGNED_INT, inds);
    glFlush();
}

void resize(int w, int h)
{
   glViewport(0, 0, w, h); 
   glMatrixMode(GL_PROJECTION);
   glLoadIdentity();
   glFrustum(-5.0, 5.0, -5.0, 5.0, 5.0, 100.0);
   glMatrixMode(GL_MODELVIEW);
}
void keyInput(unsigned char key, int x, int y)
{
   switch(key) 
   {
      case 27:
         exit(0);
         break;
      case 'x':
         Xangle += 5.0;
         if (Xangle > 360.0) Xangle -= 360.0;
         glutPostRedisplay();
         break;
      case 'X':
         Xangle -= 5.0;
         if (Xangle < 0.0) Xangle += 360.0;
         glutPostRedisplay();
         break;
      case 'y':
         Yangle += 5.0;
         if (Yangle > 360.0) Yangle -= 360.0;
         glutPostRedisplay();
         break;
      case 'Y':
         Yangle -= 5.0;
         if (Yangle < 0.0) Yangle += 360.0;
         glutPostRedisplay();
         break;
      case 'z':
         Zangle += 5.0;
         if (Zangle > 360.0) Zangle -= 360.0;
         glutPostRedisplay();
         break;
      case 'Z':
         Zangle -= 5.0;
         if (Zangle < 0.0) Zangle += 360.0;
         glutPostRedisplay();
         break;
      default:
         break;
   }
}

int main(int argc, char **argv) 
{
   glutInit(&argc, argv);

   glutInitContextVersion(2, 1); 
   glutInitContextProfile(GLUT_COMPATIBILITY_PROFILE); 

   glutInitDisplayMode(GLUT_SINGLE | GLUT_RGBA); 
   glutInitWindowSize(500, 500);
   glutInitWindowPosition(100, 100); 
   glutCreateWindow("hemisphereMultidraw.cpp");
   glutDisplayFunc(drawScene); 
   glutReshapeFunc(resize);
   glutKeyboardFunc(keyInput);
   glewExperimental = GL_TRUE; 
   glewInit(); 
   setup(); 
   glutMainLoop();  
}

EDIT 问题在于三角函数的论证！

2.0 * PI * (j/p)

应该是

2.0 * (float)(j/p) * PI 

以及其他修改，代码完美，并绘制了可爱的灯罩。

Answer 1

找到一个原因：

int i,j;
i = -1;
for(j = 0; j <= p; j++)
{
    verts[i++] = R1 * cos(2.0 * PI * (j/p));
    verts[i++] = R1 * sin(2.0 * PI * (j/p));
    verts[i++] = h;
}

i的值从-1开始，所以在这个for循环中执行的第一件事是

verts[-1] = R1 * cos(2.0 * PI * (j/p));

访问索引-1处的数组必然会导致分段错误。您的OpenGL代码看起来很好，但您肯定需要重写fillVer()和fillInd()函数。

另请参阅：Pre-increment vs post-increment