[SDL] My sprite doesn't move.
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Thread: [SDL] My sprite doesn't move.

  1. #1
    Join Date
    Feb 2009
    Posts
    23

    [SDL] My sprite doesn't move.

    Hi, i'm quite new to SDL, but i have some problems moving the sprite on keypress.
    Here's my code:
    Code:
    #ifdef __cplusplus
        #include <cstdlib>
    #else
        #include <stdlib.h>
    #endif
    #ifdef __APPLE__
    #include <SDL/SDL.h>
    #else
    #include <SDL.h>
    #endif
    
    int main ( int argc, char** argv )
    {
        // initialize SDL video
        if ( SDL_Init( SDL_INIT_VIDEO ) < 0 )
        {
            printf( "Unable to init SDL: %s\n", SDL_GetError() );
            return 1;
        }
    
        // make sure SDL cleans up before exit
        atexit(SDL_Quit);
    
        // create a new window
        SDL_Surface* screen = SDL_SetVideoMode(640, 480, 16,
                                               SDL_HWSURFACE|SDL_DOUBLEBUF);
        if ( !screen )
        {
            printf("Unable to set 640x480 video: %s\n", SDL_GetError());
            return 1;
        }
    
        // load an image
        SDL_Surface* bmp = SDL_LoadBMP("cb.bmp");
        if (!bmp)
        {
            printf("Unable to load bitmap: %s\n", SDL_GetError());
            return 1;
        }
    
        // centre the bitmap on screen
        int spr1_x = 0, spr1_y = 0;
        SDL_Rect dstrect;
        dstrect.x = spr1_x;
        dstrect.y = spr1_y;
    
        // program main loop
        bool up = false;
        bool down = false;
        bool left = false;
        bool right = false;
        bool done = false;
        while (!done)
        {
            // message processing loop
            SDL_Event event;
            while (SDL_PollEvent(&event))
            {
                // check for messages
                switch (event.type)
                {
                    // exit if the window is closed
                case SDL_QUIT:
                    done = true;
                    break;
    
                case SDL_KEYDOWN:
                    {
                        switch (event.key.keysym.sym)
                        {
                            case SDLK_LEFT:
                            left = true;
                            break;
                            case SDLK_RIGHT:
                            right = true;
                            break;
                            case SDLK_UP:
                            up = true;
                            break;
                            case SDLK_DOWN:
                            down = true;
                            break;
                            case SDLK_ESCAPE:
                            done = true;
                            break;
                            default:
                            break;
                        }
                    }
    
                    case SDL_KEYUP:
                    switch( event.key.keysym.sym )
                    {
                        case SDLK_LEFT:
                            left = false;
                            break;
                            case SDLK_RIGHT:
                            left = false;
                            break;
                            case SDLK_UP:
                            left = false;
                            break;
                            case SDLK_DOWN:
                            left = false;
                            break;
                            default:
                            break;
                    }
                } // end switch
            } // end of message processing
    
    if (left)
    {spr1_x -= 1;}
    if (right)
    {spr1_x += 1;}
    if (up)
    {spr1_y -= 1;}
    if (down)
    {spr1_y += 1;}
    
            // DRAWING STARTS HERE
    
            // clear screen
            SDL_FillRect(screen, 0, SDL_MapRGB(screen->format, 0, 0, 0));
    
            // draw bitmap
            SDL_BlitSurface(bmp, 0, screen, &dstrect);
    
            // DRAWING ENDS HERE
    
            // finally, update the screen :)
            SDL_Flip(screen);
        } // end main loop
    
        // free loaded bitmap
        SDL_FreeSurface(bmp);
    
        // all is well ;)
        printf("Exited cleanly\n");
        return 0;
    }
    Do anybody know whats wrong?

  2. #2
    Join Date
    Sep 2009
    Posts
    57

    Re: [SDL] My sprite doesn't move.

    Instead of adding the spr1_x and spr1_y by 1, you should write dstrect.x +=1 and dstrect.y += 1

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