Conways Spiel des Lebens: Fremdzellen werden gedruckt, wenn das Programm nur mit leeren/toten Zellen läuft (C/SDL2)

Question

Um es einfach auszudrücken: Wenn ich mein Game of Life Programm starte, beginnt es mit einem leeren Brett voller toter Zellen. Wenn ich die Simulation für einen einzigen Zyklus durchführe, sollte sie leer bleiben, da es keine lebenden Zellen gibt, mit denen sie umgehen kann. Wenn ich jedoch mein Programm starte, werden ein paar kleine tote Zellen in der unteren rechten Ecke "lebendig". Ich bin mir nicht sicher, warum das so ist, aber ich glaube, es liegt entweder an meiner Art, nach lebenden Zellnachbarn zu suchen, oder daran, wie ich die Zellen zeige. Hier ist ein Bild von dem, was ich meine:

#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; 
} 

Merkwürdigerweise scheint dies nur zu geschehen, wenn GRID_WIDTH und GRID_HEIGHT auf höhere Werte eingestellt sind. Es passiert, wenn beide 100 sind, und das Programm hängt/stürzt ab, wenn GRID_WIDTH auf 150 gesetzt wird, aber beide auf einen niedrigeren Wert gesetzt werden (ich habe mit 30 getestet) und alles funktioniert reibungslos.

Jede Hilfe sehr geschätzt :)

Answer 1

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

Diese Prüfung ist falsch. Wenn cy gleich GRID_HEIGHT ist oder cx gleich GRID_WIDTH ist, ist es immer noch außerhalb der Grenzen. Das liegt daran, dass die Zelle unten rechts die Koordinaten GRID_HEIGHT-1 und GRID_WIDTH-1 hat.

Natürlich sollte es sein:

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