平铺系统C ++ SDL

问题描述

我一直在使用一个平铺系统的视频游戏，我一直在设计通过C + +和SDL。代码是松散地基于lazyfoo.net上可用的教程，但使用不同的系统来绘制瓷砖到屏幕。代码工作如下：我有一个名为 Map 的类，创建另一个类 Tile 的数组。它还有一个名为 set_tiles 的函数，它从.map文件中读取数字，并将它们复制到 tile s使用两个for循环;一个用于x，一个用于y。然后我根据 Tile 的特定变量将每个表面拼接到一个临时映射。下面是实际代码：

I have been working on a tiling system for a video game I've been designing through C++ and SDL. The code is loosely based off of the tutorials available on lazyfoo.net, but with a different system to draw the tiles to the screen. The code works as follows: I have a class called Map that creates an array of another class called Tile. It also has a function called set_tiles that reads numbers from a .map file and copies them to the array of tile's using two for loops; one for the x's and one for the y's. I then blit each surface to a temporary map according to the Tile's specific variables. Here is the actual code:

SDL_Surface* Map::set_tiles ( SDL_Surface* tile_image ) {
Setup setup;

SDL_Surface* temp_map = NULL;

//Open the map
std::ifstream map ( "Test.map" );

//Catch any errors
if ( map.fail() ) return NULL;

//Initialize the tiles
for ( int y = 0; y < MAP_HEIGHT / TILE_HEIGHT; y++ ) {
    for ( int x = 0; x < MAP_WIDTH / TILE_WIDTH; x++ ) {
        //Determines the tile type
        int tile_type = -1;

        //Read the tile type from the map
        map >> tile_type;

        //Make sure it's a real tile
        if ( tile_type < 0 || tile_type >= TILE_SPRITES ) {
            map.close();
            return NULL;
        }

        //Error check for the .map file
        if ( map.fail() ) {
            map.close();
            return NULL;
        }

        //Add the tile to the array
        tile_array[x][y] = &Tile ( x, y, tile_type );

        //Create the temp. image crop
        SDL_Rect* temp_crop = &tile_array[x][y]->get_crop();

        //Check for crop errors
        if ( ( temp_crop->h || temp_crop->w ) == 0 ) return NULL;

        //Edit the temp. map
        setup.apply_surface ( x * TILE_WIDTH, y * TILE_HEIGHT, tile_image, temp_map, temp_crop );
    }
}

map.close();

//Return the modified map
return temp_map;

}

Tile::Tile ( int x, int y, int tile_type ) {
//Get the offsets
box.x = x;
box.y = y;

//Set the collision box
box.w = TILE_WIDTH;
box.h = TILE_HEIGHT;

//Get the tile type
type = tile_type;

//Choose the crop option
crop.w = TILE_WIDTH;
crop.h = TILE_HEIGHT;

switch ( tile_type ) {
case TILE_RED:
    crop.x = 0 * TILE_WIDTH;
    crop.y = 0 * TILE_HEIGHT;
    break;
case TILE_GREEN:
    crop.x = 1 * TILE_WIDTH;
    crop.y = 0 * TILE_HEIGHT;
    break;
case TILE_BLUE:
    crop.x = 2 * TILE_WIDTH;
    crop.y = 0 * TILE_HEIGHT;
    break;
case TILE_CENTER:
    crop.x = 3 * TILE_WIDTH;
    crop.y = 0 * TILE_HEIGHT;
    break;
case TILE_TOP:
    crop.x = 0 * TILE_WIDTH;
    crop.y = 1 * TILE_HEIGHT;
    break;
case TILE_TOPRIGHT:
    crop.x = 1 * TILE_WIDTH;
    crop.y = 1 * TILE_HEIGHT;
    break;
case TILE_RIGHT:
    crop.x = 2 * TILE_WIDTH;
    crop.y = 1 * TILE_HEIGHT;
    break;
case TILE_BOTTOMRIGHT:
    crop.x = 3 * TILE_WIDTH;
    crop.y = 1 * TILE_HEIGHT;
    break;
case TILE_BOTTOM:
    crop.x = 0 * TILE_WIDTH;
    crop.y = 2 * TILE_HEIGHT;
    break;
case TILE_BOTTOMLEFT:
    crop.x = 1 * TILE_WIDTH;
    crop.y = 2 * TILE_HEIGHT;
    break;
case TILE_LEFT:
    crop.x = 2 * TILE_WIDTH;
    crop.y = 2 * TILE_HEIGHT;
    break;
case TILE_TOPLEFT:
    crop.x = 3 * TILE_WIDTH;
    crop.y = 2 * TILE_HEIGHT;
    break;
}

}

问题是 set_tiles 在调用时返回一个NULL指针。通过一点调试，我发现它使它一路到底，然后返回一个NULL，它不在do的某个地方在for循环。我也尝试将所有 tile crop.x's和y的设置为0，只是为了看它是否可以工作，但不是。

The problem is that set_tiles returns a NULL pointer when it is called. Through a bit of debugging I found that it makes it all the way to the end and then returns a NULL, it doesn't do it somewhere in the for loops. I've also tried setting all tile crop.x's and y's to 0, just to see if it would work, but it doesn't.

注意
问题不是我的图片或.map文件。
我认为我的指针的理解可能有点错误，并且我可能在调用 apply_surface 时犯了一个错误。

void Setup::apply_surface ( int x, int y, SDL_Surface* source, SDL_Surface* &destination, SDL_Rect* clip ) {
//Temporary rectangle to hold the offsets
SDL_Rect offset;

//Get the offsets
offset.x = x;
offset.y = y;

//Blit the surface
SDL_BlitSurface ( source, clip, destination, &offset );

}

推荐答案

SDL_BlitSurface 将表面对齐到另一个表面。它们都必须初始化，否则函数什么也不做。你传递一个NULL指针。您需要通过调用类似于的方式初始化指针。

SDL_BlitSurface blits one surface to another. They both must be initialized, otherwise the function does nothing. You are passing a NULL pointer to it. You need to initialize the pointer with a call to something like SDL_CreateRGBSurface.

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