SDL中由SDL_Rect向量分割曲面的问题

Question

#include "main.h"
SDL_Surface* screen; //The screen Surface
SDL_Surface* Snake_Body; //The snake surface (shape to draw)
SDL_Rect rectangle1; //Red border
SDL_Rect rectangle2; //Black Board
SDL_Event event;    //Keyboard handling
direction facing;
std::vector<SDL_Rect> snake (3); //Snake body locations

SDL_Surface *LoadSnake()
{
    SDL_Surface* temporary;
    Uint32 rmask,gmask,bmask,amask;
    #if SDL_BYTEORDER == SDL_BIG_ENDIAN
        rmask = 0xff000000;
        gmask = 0x00ff0000;
        bmask = 0x0000ff00;
        amask = 0x000000ff;
    #else
        rmask = 0x000000ff;
        gmask = 0x0000ff00;
        bmask = 0x00ff0000;
        amask = 0xff000000;
    #endif
    temporary = SDL_CreateRGBSurface(SDL_SWSURFACE,5,5,32,rmask,gmask,bmask,amask); //Make an empty surface
    SDL_FillRect(temporary,NULL,SDL_MapRGB(screen->format,0,255,0)); //Fill it with color
    return temporary; //return it
}

bool init()
{
    if(SDL_Init(SDL_INIT_EVERYTHING) == -1 )
        return false;
    screen = SDL_SetVideoMode(SCREEN_WIDTH,SCREEN_HEIGHT,SCREEN_BPP,SDL_SWSURFACE);
    if(!screen)
        return false;
    SDL_WM_SetCaption("Snake v0.1",NULL);
    Snake_Body = LoadSnake();
    rectangle1.x = 0;  //Red border
    rectangle1.y = 0;
    rectangle1.w = 500;
    rectangle1.h = 500;
    rectangle2.x = 25; //Black background
    rectangle2.y = 25;
    rectangle2.w = 450;
    rectangle2.h = 450;
    return true;
}
SDL_Surface *loadImage(const char* filename)
{
    SDL_Surface *loadedImage = NULL;
    SDL_Surface *optimizedImage = NULL;
    loadedImage = SDL_LoadBMP(filename);
    if (loadedImage)
    {
        optimizedImage = SDL_DisplayFormat(loadedImage);
        SDL_FreeSurface(loadedImage);
    }
    return optimizedImage;
}
void pollInput()
{
    while(SDL_PollEvent(&event))
    {
        if(event.type == SDL_QUIT)
        {
            end = true;
        }
        if(event.type == SDL_KEYUP)
        {
            switch(event.key.keysym.sym)
            {
            case SDLK_ESCAPE:
                end = true; break;
            case SDLK_UP:
                facing = up; break;
            case SDLK_DOWN:
                facing = down; break;
            case SDLK_RIGHT:
                facing = right; break;
            case SDLK_LEFT:
                facing = left; break;
            }
        }
    }
}
void Update()
{
    for(unsigned int i = 1; i < snake.size(); i++)
    {
        snake[i] = snake[i-1];
    }
    switch(facing)
    {
    case up:
        snake[0].y -= 5; break;
    case down:
        snake[0].y += 5; break;
    case left:
        snake[0].x -= 5; break;
    case right:
        snake[0].x += 5; break;
    }
}
void SetUp()
{
    snake[0].x = 250;
    snake[0].y = 250;

    snake[1].x = 250 + 15;
    snake[1].y = 250;
    snake[2].x = 250 + 15 + 15;
    snake[2].y = 250;
}
void Draw()
{
    unsigned short i;
    int x;
    SDL_FillRect(screen,&rectangle1,SDL_MapRGB(screen->format,255,0,0)); //Red Border
    SDL_FillRect(screen,&rectangle2,SDL_MapRGB(screen->format,0,0,0)); //Black Board
    for(i = 0; i < snake.size(); i++)
    {
        assert(SDL_BlitSurface(Snake_Body,NULL,screen,&snake[i]) == 0);
    }
    SDL_Flip(screen);
}
void Finish()
{
    SDL_FreeSurface(Snake_Body);
    SDL_Quit();
}

我有这个代码，这是一个游戏的蛇写在SDL我正在工作，然而，我似乎有一个问题。

SDL可以很好地绘制背景，但是由于某些原因它不能绘制蛇。我在那里设置了一个断言来检查SDL_BlitSurface函数是否成功，并且它返回一个正常值(0)，即使屏幕上没有显示任何内容。

我将蛇节点的纹理设置为单个绿色矩形Snake_Body，并将需要在std::vector容器中绘制的位置编码，因此我可以在向量中的每个元素上调用SDL_BlitSurface()函数，我已经跟踪了值，它们正在正确地变化，但出于某种原因，图像仍然没有绘制。我还尝试用相同位置的SDL_FillRect()替换我的SDL_BlitSurface()函数，但它不会改变任何东西。

编辑:我在下面添加了我的主循环:

#include "main.h"
bool end = false;
Uint32 time;
int main(int argc,char* argv[])
{
    if(!init())
        return 1;
    SetUp();
    time = SDL_GetTicks();
    while(!end)
    {
        if(time+1000<SDL_GetTicks())
        {
            Update();
            time = SDL_GetTicks();
        }
        pollInput();
        Draw();
    }
    Finish();
    return 0;
}

Answer 1

你似乎没有对蛇的位置做任何边界检查，以确保它留在屏幕上。所以当它离开屏幕时，它保持关闭，永远不会回来。我的猜测是你没有正确地调节帧率，或者你根本没有调节它(我需要看到你的主循环)，所以蛇离开屏幕的速度如此之快，以至于你甚至都看不到它。

如果不调用Update函数会发生什么?

Answer 2

如果你张贴了整个代码，那么有一个调用SetUp缺失。这不会设置蛇，它可能在屏幕外的某个地方，因为矢量包含垃圾。此外，尽管SDL_BlitSurface忽略了直街宽度和高度，但最好将它们初始化为一些有意义的值。