c++ - OpenGL 程序的段错误

Question

我正在尝试绘制 Sierpinski carpet plane fractal使用 OpenGL，但我的程序不断收到 SegFault 错误。

我的代码如下:

#include <GL/gl.h>
#include <GL/glut.h>
#include <stdlib.h>
#include <math.h>


class GLintPoint
{
public:
    GLint x, y;
};

int random(int m)
{
    return rand() % m;
}

void drawDot(GLint x, GLint y)
{
    glBegin(GL_POINTS);
    glVertex2i(x, y);
    glEnd();
}

void init()
{
    glClearColor(1.0, 1.0, 1.0, 0.0);
    glColor3f(0.0, 0.0, 0.0);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluOrtho2D(0.0, 640.0, 0.0, 480.0);
}


int isSierpinskiCarpetPixelFilled(int x, int y, int width, int height)
{

        GLintPoint point;

        // base case 1 of 2
        if ((x <= 0)||(y <= 0)||(x>=width)||(y>=height)) //top row or left column or out of bounds should be full
        {
            point.x = x;
            point.y = y;
            drawDot(point.x, point.y);
        }
        {
                /*
                If the grid was split in 9 parts, what part(x2,y2) would x,y fit into?
                */
                int x2 = x * 3 / width; // an integer from 0..2 inclusive
                int y2 = y * 3 / height; // an integer from 0..2 inclusive

                // base case 2 of 2
                if (x2 == 1 && y2 == 1) // if in the center square, it should be empty
                        return 0;

                // general case

                /* offset x and y so it becomes bounded by 0..width/3 and 0..height/3
                and prepares for recursive call
                some offset is added to make sure the parts have all the correct size when
                width and height isn't divisible by 3 */

                x -= (x2 * width+2)  / 3;
                y -= (y2 * height+2) / 3;
                width  = (width +2-x2)/3;
                height = (height+2-y2)/3;
        }


        return isSierpinskiCarpetPixelFilled(x, y, width, height);
}

void drawSierpinskiCarpet()
{
    glClear(GL_COLOR_BUFFER_BIT);
    glColor3f(0.0, 1.0, 0.0);

    int x = 50;
    int y = 50;

    isSierpinskiCarpetPixelFilled(x,y,50,50);

    glFlush();

}


int main(int argc, char *argv[])
{
    glutInit(&argc, argv);
    glutInitWindowSize(640,480);
    glutInitWindowPosition(10,10);
    glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
    glutCreateWindow("The Sierpinski Carpet");
    glutDisplayFunc(drawSierpinskiCarpet);
    init();
    glutMainLoop();
    return EXIT_SUCCESS;
}

Answer 1

很可能出现堆栈溢出。它似乎在无限递归。每次调用 isSierpinskiCarpetPixelFilled 都会导致另一个调用:

    return isSierpinskiCarpetPixelFilled(x, y, width, height);

对于给定的输入值，输入参数(按顺序)将是:

50, 50, 50, 50
0, 0, 16, 16
0, 0, 6, 6
0, 0, 2, 2
0, 0, 1, 1
0, 0, 1, 1
... (until stack overflow)