康威的生命游戏 : extraneous cells being printed when program run with only blank/dead cells (C/SDL2)

Question

简单地说:当运行我的生命游戏程序时，它从一 block 空的死细胞板开始。如果我运行一个周期的模拟，它应该保持为空，因为没有活细胞可供它处理。然而，当我运行我的程序时，右下角的一些小死细胞变得“活跃”。我不确定这是为什么，但我相信这要么是由于我检查活细胞邻居的方式，要么是由于我显示细胞的方式。这是我的意思的图片:

#include <SDL.h>
#include <stdio.h>
#include <stdbool.h>

#define CELL_SIZE 10
#define GRID_WIDTH 100
#define GRID_HEIGHT 100
#define SCREEN_WIDTH (GRID_WIDTH * CELL_SIZE)
#define SCREEN_HEIGHT (GRID_HEIGHT * CELL_SIZE)

typedef enum {ALIVE, DEAD} State;
typedef struct{
    int x;
    int y;
    State state;
} Cell;

// SDL related functions
SDL_Window *createWindow(char *title);
SDL_Renderer *createRenderer(SDL_Window *window);
void drawGrid(SDL_Renderer *r);
void drawCells(SDL_Renderer *r, int a[][GRID_WIDTH]);

// Game of Life functions
void updateCells(int a[][GRID_WIDTH]); // takes cells array as input
int countLivingNeighbours(int a[][GRID_WIDTH], int x, int y);

int main(int argc, char *argv[]){
    // Initialise SDL
    SDL_Init(SDL_INIT_VIDEO);

    // Create window and renderer
    SDL_Window *window = createWindow("Game of Life");
    SDL_Renderer *renderer = createRenderer(window);

    // Setup event handling + mouse co-ordinate handling
    SDL_Event event;
    int mouseX, mouseY;
    bool mouse_left_down = false;
    bool mouse_right_down = false;

    // Set all cells to initial state of dead
    int cells[GRID_HEIGHT][GRID_WIDTH];
    int cx, cy;
    for(cy = 0; cy < GRID_HEIGHT; cy++){
        for(cx = 0; cx < GRID_WIDTH; cx++){
            cells[cy][cx] = DEAD;
        }
    }

    // MAIN LOOP //
    while(1){
        // Handle events/input
        while(SDL_PollEvent(&event) != 0){
            switch(event.type){
                case SDL_QUIT: // Check if user has quit
                    return 1;

                // Check if user is HOLDING left or right mouse button
                case SDL_MOUSEBUTTONDOWN: case SDL_MOUSEBUTTONUP:
                    switch(event.button.button){
                        case SDL_BUTTON_LEFT: mouse_left_down = !mouse_left_down; break;
                        case SDL_BUTTON_RIGHT: mouse_right_down = !mouse_right_down; break;
                    }

                // If user presses space, simulate a single change
                case SDL_KEYDOWN:
                    if(event.key.keysym.sym == SDLK_SPACE)
                        updateCells(cells);

            }
        }

        // Get user mouse button input - left click gives life to cell at current co-ords, right click kills
        SDL_GetMouseState(&mouseX, &mouseY);
        if(mouse_left_down == true)
            cells[mouseY / CELL_SIZE][mouseX / CELL_SIZE] = ALIVE;
        else if(mouse_right_down == true)
            cells[mouseY / CELL_SIZE][mouseX / CELL_SIZE] = DEAD;

        // Set screen colour to white
        SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);

        // Render white to screen (clear screen)
        SDL_RenderClear(renderer);

        // Draw the grid and living cells
        drawGrid(renderer);
        drawCells(renderer, cells);

        // Update screen
        SDL_RenderPresent(renderer);
    }

    // Exit SDL and SDL_image
    SDL_Quit();
    return 0;
}

/*
1. Any live cell with fewer than two live neighbours dies, as if caused by underpopulation.
2. Any live cell with two or three live neighbours lives on to the next generation.
3. Any live cell with more than three live neighbours dies, as if by overpopulation.
4. Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.
*/
void updateCells(int a[][GRID_WIDTH]){
    int new[GRID_HEIGHT][GRID_WIDTH];
    int cy, cx; // vertical count, horizontal count

    for(cy = 0; cy < GRID_HEIGHT; cy++){
        for(cx = 0; cx < GRID_WIDTH; cx++){
            // Any live cell with fewer than two live neighbours dies, as if caused by underpopulation.
            if(a[cy][cx] == ALIVE && countLivingNeighbours(a, cx, cy) < 2)
                new[cy][cx] = DEAD;

            // Any live cell with two or three live neighbours lives on to the next generation.
            else if(a[cy][cx] == ALIVE && (countLivingNeighbours(a, cx, cy) == 2 || countLivingNeighbours(a, cx, cy) == 3))
                new[cy][cx] = ALIVE;

            // Any live cell with more than three live neighbours dies, as if by overpopulation.
            else if(a[cy][cx] == ALIVE && countLivingNeighbours(a, cx, cy) > 3)
                new[cy][cx] = DEAD;

            // Any dead cell with exactly three live neighbours becomes a live cell, as if by reproduction.
            else if(a[cy][cx] == DEAD && countLivingNeighbours(a, cx, cy) == 3)
                new[cy][cx] = ALIVE;

            else
                new[cy][cx] = DEAD;
        }
    }

    // Update all cells into new states
    for(cy = 0; cy < GRID_HEIGHT; cy++){
        for(cx = 0; cx < GRID_WIDTH; cx++){
            a[cy][cx] = new[cy][cx];
        }
    }
}

// THERE'S NO ERROR CHECKING HERE WHICH IS BAD
// Should ideally check if a cell even exists before checking its state
int countLivingNeighbours(int a[][GRID_WIDTH], int x, int y){
    int count = 0, cx, cy;

    for(cy = y - 1; cy <= y + 1; cy++){
        for(cx = x - 1; cx <= x + 1; cx++){

            // Ensure neighbouring cell is not out of bounds
            if(!(cy < 0 || cx < 0 || cy > GRID_HEIGHT || cx > GRID_WIDTH)){
                // If there is a living neighbouring cell, add to count
                if(a[cy][cx] == ALIVE)
                    count++;

                // disregard current cell as it is not a neighbour
                if(a[cy][cx] == ALIVE && cx == x && cy == y)
                    count--;
            }


        }
    }

    return count;
}

void drawGrid(SDL_Renderer *r){
    // Draw vertical grid lines
    for(int v = CELL_SIZE; v < SCREEN_WIDTH; v += CELL_SIZE){
        // Set draw colour to grey
        SDL_SetRenderDrawColor(r, 110, 110, 110, 110);

        // Draw vertical line
        SDL_RenderDrawLine(r, v, 0, v, SCREEN_HEIGHT);
    }

    // Draw horizontal grid lines
    for(int h = CELL_SIZE; h < SCREEN_HEIGHT; h += CELL_SIZE){
        // Set draw colour to grey
        SDL_SetRenderDrawColor(r, 110, 110, 110, 110);

        // Draw horizontal line
        SDL_RenderDrawLine(r, 0, h, SCREEN_WIDTH, h);
    }
}

void drawCells(SDL_Renderer *r, int a[][GRID_WIDTH]){
    // Define cell width/height
    SDL_Rect cellRect;
    cellRect.w = CELL_SIZE + 1; // Same size as one cell +1 so it covers the grid line fully
    cellRect.h = CELL_SIZE + 1; // Same size as one cell +1 so it covers the grid line fully

    // Draw living cells
    int cx, cy;
    for(cy = 0; cy < GRID_HEIGHT; cy++){
        for(cx = 0; cx < GRID_WIDTH; cx++){
            if(a[cy][cx] == ALIVE){
                // Set cell x/y pos
                cellRect.x = cx * CELL_SIZE;
                cellRect.y = cy * CELL_SIZE;

                SDL_SetRenderDrawColor(r, 0, 0, 0, 0);
                SDL_RenderFillRect(r, &cellRect);
            }
        }
    }
}

SDL_Window *createWindow(char *title){
    SDL_Window *window = SDL_CreateWindow(
        title,                  // Title
        SDL_WINDOWPOS_CENTERED, // Initial window x position
        SDL_WINDOWPOS_CENTERED, // Initial window y position
        SCREEN_WIDTH,           // Window Width
        SCREEN_HEIGHT,          // Window Height
        0                       // Flags
    );

    if(window == NULL){
        printf("Failed to create window. %s\n", SDL_GetError());
        exit(EXIT_FAILURE);
    }

    return window;
}

SDL_Renderer *createRenderer(SDL_Window *window){
    SDL_Renderer *renderer = SDL_CreateRenderer(
        window,                     // Window
        -1,                         // Monitor index (-1 for first available)
        SDL_RENDERER_ACCELERATED    // Flags
    );

    if(renderer == NULL){
        printf("Failed to create renderer. %s\n", SDL_GetError());
        exit(EXIT_FAILURE);
    }

    return renderer;
}

奇怪的是，这似乎只在 GRID_WIDTH 和 GRID_HEIGHT 设置为更高的值时才会发生。当两者都是 100 时，就会发生这种情况，如果 GRID_WIDTH 设置为 150，程序就会挂起/崩溃，但将它们都设置为较低的值(我测试为 30)，一切都会顺利进行。

非常感谢任何帮助:)

Answer 1

       // Ensure neighbouring cell is not out of bounds
       if(!(cy < 0 || cx < 0 || cy > GRID_HEIGHT || cx > GRID_WIDTH)){

这个检查是错误的。如果 cy 等于 GRID_HEIGHT 或 cx 等于 GRID_WIDTH，它仍然超出范围。这是因为右下角单元格的坐标为 GRID_HEIGHT-1 和 GRID_WIDTH-1。

当然应该是:

       if(!(cy < 0 || cx < 0 || cy >= GRID_HEIGHT || cx >= GRID_WIDTH)){