Map is rendering too slow

Question

I have a basic 20x20 array that stores the map for my game. It either has a 1 or 0 to say a path and a non path. When I draw it on the screen, It seems to take to long to draw one at a time and looks like a snake is being loaded on the screen. I need them drawing faster.

Set up the screen array

for(int i=0; i<sizeOfArray; i++)
    {
        for(int j=0; j<sizeOfArray; j++)
        {
            if (LevelOne[i][j]==0)//Path
            {
                screenChunks[i][j].Set(i*40,j*40,"Path.bmp", screen);
            }
            if (LevelOne[i][j]==1)//Wall
            {
                screenChunks[i][j].Set(i*40,j*40,"Wall.bmp", screen);
            }
            if (LevelOne[i][j]==2) //Hero
            {
                screenChunks[i][j].Set(i*40,j*40,"Hero.bmp", screen);
            }
        }
    }

Draw the sprites

for(int i=0; i<sizeOfArray; i++)
    {
        for(int j=0; j<sizeOfArray; j++)
        {
            screenChunks[i][j].Draw();
        }
    }

    //Dynamically drawn each time
    SDL_FillRect(screen,0,0);

    //Hero Start Position
    hero.Draw();

    SDL_Delay(60);

Sprite.cpp Draw Method

void Sprite::Draw()
{
SDL_Rect offset;

//Give the offsets to the rectangle
offset.x = PosX;
offset.y = PosY;

//Blit the surface
SDL_BlitSurface( sprite, NULL, Screen, &offset );

Height = offset.h;
Width = offset.w;

SDL_UpdateRect(Screen, 0,0,0,0);

}

Sprite Setter

void Sprite::Set(int posX, int posY, string imagePath, SDL_Surface *screen)
{
PosX = posX;
PosY = posY;
ImagePath = imagePath;
Screen = screen;

if(ImagePath == "")
    return;

char * writable = new char [ImagePath.size()+1];
strcpy (writable, ImagePath.c_str());

temp = SDL_LoadBMP(writable);
sprite = SDL_DisplayFormat(temp);
SDL_FreeSurface(temp);
// free the string after using it
delete[] writable;
}

Answer 1

Loading an image from disk every time you need to draw it is a bad idea. Terrible, in fact. Try loading once and reusing it.

Also, please have a look at calling SDL_UpdateRect(Screen, 0,0,0,0); on every sprite draw...

BTW, if you're doing the whole "writable" thing because ImagePath is an std::string and SDL_LoadBMP accepts char*, then you should google the c_str() method.

Answer 2

For loading images only once, check out http://stackoverflow.com/questions/1729699/how-do-i-correctly-use-sdl-freesurface-when-dealing-with-a-vector-of-surfaces which introduces the idea of an image_cache.

I've expanded on this on my blog here and then again once I'd updated my design to break up the class into smaller more manageable pieces here