c++ - 递归似乎仅在某种程度上起作用-如何调试此类问题？

Question

我目前正在编写程序，使用递归方法绘制Sierpinski地毯。我的程序代码如下:

#include <iostream>
#include <stdio.h>

const int L = 4;
const int N = 81;
unsigned char output[N][N][3];

void prepareBoard()
{
    for (size_t y = 0; y < N; y++)
    {
        for (size_t x = 0; x < N; x++)
        {
            output[y][x][0] = 0;
            output[y][x][1] = 0;
            output[y][x][2] = 0;
        }
    }
}

void drawRed(int x, int y)
{
    output[x][y][0] = 255;
    output[x][y][1] = 0;
    output[x][y][2] = 0;
}

void drawCarpet(int y, int x, int length, int l)
{
    if (l < L)
    {
        int x1, x2;
        int part = length / 3;
        for (size_t i = 0; i < length; i++)
        {
            for (size_t j = 0; j < length; j++)
            {
                if (i > part && i < part * 2 && j > part && j < part * 2)
                {
                    drawRed(i+x, j+y);
                }
            }
            x1 = x + part;
            x2 = x + part * 2;
            drawCarpet(x, x, part, l + 1);   // 0 0
            drawCarpet(x1, x, part, l + 1);  // 9 0
            drawCarpet(x2, x, part, l + 1);  // 17 0
            drawCarpet(x, x1, part, l + 1);  // 0 9
            drawCarpet(x2, x1, part, l + 1);  // 0 17
            drawCarpet(x, x2, part, l + 1); // 9 17
            drawCarpet(x1, x2, part, l + 1); //
            drawCarpet(x2, x2, part, l + 1); //
        }
    }
}

int main()
{
    FILE *fp;
    fp = fopen("output.ppm", "wb");
    fprintf(fp, "P6\n %s\n %d\n %d\n %d\n", "# ", N, N, 255);

    prepareBoard();
    drawCarpet(0, 0, N, 0);

    for (size_t y = 0; y < N; y++)
    {
        for (size_t x = 0; x < N; x++)
        {
            fwrite(output[y][x], 1, 3, fp);
        }
    }

    fclose(fp);
    return 0;
}

我如何启动该功能:

drawCarpet(0, 0, 243, 0);

问题是该函数可以正常工作到第二个深度-然后它仅在两个“子正方形”上开始工作。这是程序的输出。

我欢迎任何建议，尤其是在解决此类问题的方法上。我在中间找到像素的算法也不尽人意，我也很乐意就此提出一些建议。

Answer 1

还没有测试过，但我相信问题在于递归调用中-您不使用y。

        x1 = x + part;
        x2 = x + part * 2;
        drawCarpet(x, x, part, l + 1);  // why no dependency on y?
        drawCarpet(x1, x, part, l + 1);  
        drawCarpet(x2, x, part, l + 1); 
        drawCarpet(x, x1, part, l + 1);  
        drawCarpet(x2, x1, part, l + 1);  
        drawCarpet(x, x2, part, l + 1); 
        drawCarpet(x1, x2, part, l + 1); 
        drawCarpet(x2, x2, part, l + 1); 

应该是这样的:

        x1 = x + part;
        x2 = x + part * 2;
        y1 = y + part;
        y2 = y + part*2;
        drawCarpet(x, y, part, l + 1);
        drawCarpet(x1, y, part, l + 1);  
        drawCarpet(x2, y, part, l + 1); 
        drawCarpet(x, y1, part, l + 1);  
        drawCarpet(x2, y1, part, l + 1);  
        drawCarpet(x, y2, part, l + 1); 
        drawCarpet(x1, y2, part, l + 1); 
        drawCarpet(x2, y2, part, l + 1);