SDL + Keys

Hi peeps!

My program, which i'm about to post, doesn't work. Why is that?
It sais: 142 C:\Users\Fredrik\Desktop\Saker\Projekt\C++\SDL\Lea rn 1\main.cpp void value not ignored as it ought to be

And it's not the only error of that sort. There is like 4 errors of that sort, and thats the only errors. Why am i getting theese errors?

Code:

---

//The headers
#include "SDL/SDL.h"
#include <string>

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The surfaces
SDL_Surface *background = NULL;
SDL_Surface *message = NULL;
SDL_Surface *screen = NULL;
SDL_Surface *piece = NULL;
SDL_Surface *up = NULL;
SDL_Surface *down = NULL;
SDL_Surface *left = NULL;
SDL_Surface *right = NULL;

//The event structure
SDL_Event event;

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;
   
    //The optimized surface that will be used
    SDL_Surface* optimizedImage = NULL;
   
    //Load the image
    loadedImage = SDL_LoadBMP( filename.c_str() );
   
    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized surface
        optimizedImage = SDL_DisplayFormat( loadedImage );
       
        //Free the old surface
        SDL_FreeSurface( loadedImage );
    }
   
    //Return the optimized surface
    return optimizedImage;
}

void apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL )
{
    //Holds offsets
    SDL_Rect offset;
   
    //Get offsets
    offset.x = x;
    offset.y = y;
   
    //Blit
    SDL_BlitSurface( source, clip, destination, &offset );
}

bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;   
    }
   
    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
   
    //If there was in error in setting up the screen
    if( screen == NULL )
    {
        return false;   
    }
   
    //Set the window caption
    SDL_WM_SetCaption( "Walk-around-game", NULL );
   
    //If everything initialized fine
    return true;
}

bool load_files()
{
    //Load the background image
    background = load_image( "bg.bmp" );
    piece = load_image( "piece.bmp" );
   
    //If there was a problem in loading the background
    if( background == NULL )
    {
        return false;   
    }
   
    //If there was a problem in loading the background
    if( piece == NULL )
    {
        return false;   
    }
   
    //If everything loaded fine
    return true;
}

void clean_up()
{
    //Free the surfaces
    SDL_FreeSurface( background );
    SDL_FreeSurface( message );
    SDL_FreeSurface( piece );
    SDL_FreeSurface( up );
    SDL_FreeSurface( down );
    SDL_FreeSurface( left );
    SDL_FreeSurface( right );
   
    //Quit SDL
    SDL_Quit();
}

int main( int argc, char* args[] )
{
    //Quit flag
    bool quit = false;
   
    //Initialize
    if( init() == false )
    {
        return 1;
    }
   
    //Load the files
    if( load_files() == false )
    {
        return 1;
    }
   
    apply_surface( 10, 10, piece, screen );
   
    //Generate the message surfaces
    up = apply_surface( 10, 0, piece, screen );
    down = apply_surface( 10, 20, piece, screen );
    left = apply_surface( 0, 10, piece, screen );
    right = apply_surface( 20, 10, piece, screen );
   
    //Apply the background
    apply_surface( 0, 0, background, screen );
   
    //While the user hasn't quit
    while( quit == false )
    {
        //If there's an event to handle
        if( SDL_PollEvent( &event ) )
        {
            //If a key was pressed
            if( event.type == SDL_KEYDOWN )
            {
                //Set the proper message surface
                switch( event.key.keysym.sym )
                {
                    case SDLK_UP: message = up; break;
                    case SDLK_DOWN: message = down; break;
                    case SDLK_LEFT: message = left; break;
                    case SDLK_RIGHT: message = right; break;   
                }
            }
           
            //If the user has Xed out the window
            else if( event.type == SDL_QUIT )
            {
                //Quit the program
                quit = true;
            }
        }
       
        //If a message needs to be displayed
        if( message != NULL )
        {
            //Apply the background to the screen
            apply_surface( 0, 0, background, screen );
           
            //Null the surface pointer
            message = NULL;
        }
   
        //Update the screen
        if( SDL_Flip( screen ) == -1 )
        {
            return 1;   
        }
    }
       
    //Clean up
    clean_up();
   
    return 0;   
}

---

I think it has to do with the key thing.

Code:

---

    up = apply_surface( 10, 0, piece, screen );
    down = apply_surface( 10, 20, piece, screen );
    left = apply_surface( 0, 10, piece, screen );
    right = apply_surface( 20, 10, piece, screen );

---

I really(!) need help! Ty!

Well, up, down, right, left and message are pointers to SDL_Surface. First of all, the names you chose for the variables doesn't exactly make it easy to understand their type. The fact that a variable called "message" actually doesn't hold a message but an image is really confusing.

Second, apply_surface returns void. It's quite easy to see that "void" != "SDL_Surface*". That's why you get errors.

I've really got no clue what this is supposed to do, but maybe you meant to do something like this?

Code:

---

apply_surface(10, 0, piece, up);
apply_surface(10, 20, piece, down);
// and so on

---

Moved to game programming forum.

SDL is for game programming therefore this belongs on the game programming forum.

Ok, now it starting to get better. But i can't move the piece. Why is that? =)

Code:

---

//The headers
#include "SDL/SDL.h"
#include <string>

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The surfaces
SDL_Surface *background = NULL;
SDL_Surface *holder = NULL;
SDL_Surface *screen = NULL;
SDL_Surface *piece = NULL;
SDL_Surface *up = NULL;
SDL_Surface *down = NULL;
SDL_Surface *left = NULL;
SDL_Surface *right = NULL;

//The event structure
SDL_Event event;

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;
   
    //The optimized surface that will be used
    SDL_Surface* optimizedImage = NULL;
   
    //Load the image
    loadedImage = SDL_LoadBMP( filename.c_str() );
   
    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized surface
        optimizedImage = SDL_DisplayFormat( loadedImage );
       
        //Free the old surface
        SDL_FreeSurface( loadedImage );
    }
   
    //Return the optimized surface
    return optimizedImage;
}

SDL_Surface *apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL )
{
    //Holds offsets
    SDL_Rect offset;
   
    //Get offsets
    offset.x = x;
    offset.y = y;
   
    //Blit
    SDL_BlitSurface( source, clip, destination, &offset );
}

bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;   
    }
   
    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
   
    //If there was in error in setting up the screen
    if( screen == NULL )
    {
        return false;   
    }
   
    //Set the window caption
    SDL_WM_SetCaption( "Walk-around-game", NULL );
   
    //If everything initialized fine
    return true;
}

bool load_files()
{
    //Load the background image
    background = load_image( "bg.bmp" );
    piece = load_image( "piece.bmp" );
   
    //If there was a problem in loading the background
    if( background == NULL )
    {
        return false;   
    }
   
    //If there was a problem in loading the background
    if( piece == NULL )
    {
        return false;   
    }
   
    //If everything loaded fine
    return true;
}

void clean_up()
{
    //Free the surfaces
    SDL_FreeSurface( background );
    SDL_FreeSurface( holder );
    SDL_FreeSurface( piece );
    SDL_FreeSurface( up );
    SDL_FreeSurface( down );
    SDL_FreeSurface( left );
    SDL_FreeSurface( right );
   
    //Quit SDL
    SDL_Quit();
}

int main( int argc, char* args[] )
{
    //Quit flag
    bool quit = false;
   
    //Initialize
    if( init() == false )
    {
        return 1;
    }
   
    //Load the files
    if( load_files() == false )
    {
        return 1;
    }
   
    //Generate the new way
    up = apply_surface( 10, 0, piece, screen );
    down = apply_surface( 10, 20, piece, screen );
    left = apply_surface( 0, 10, piece, screen );
    right = apply_surface( 20, 10, piece, screen );
   
    //Apply the background
    apply_surface( 0, 0, background, screen );
   
    //Apply the piece
    apply_surface( 10, 10, piece, screen );
   
    //While the user hasn't quit
    while( quit == false )
    {
        //If there's an event to handle
        if( SDL_PollEvent( &event ) )
        {
            //If a key was pressed
            if( event.type == SDL_KEYDOWN )
            {
                //Set the proper holder surface
                switch( event.key.keysym.sym )
                {
                    case SDLK_UP: holder = up; break;
                    case SDLK_DOWN: holder = down; break;
                    case SDLK_LEFT: holder = left; break;
                    case SDLK_RIGHT: holder = right; break;   
                }
            }
           
            //If the user has Xed out the window
            else if( event.type == SDL_QUIT )
            {
                //Quit the program
                quit = true;
            }
        }
       
        //If a holder needs to be displayed
        if( holder != NULL )
        {
            //Apply the background to the screen
            apply_surface( 0, 0, background, screen );
           
            //Null the surface pointer
            holder = NULL;
        }
   
        //Update the screen
        if( SDL_Flip( screen ) == -1 )
        {
            return 1;   
        }
    }
       
    //Clean up
    clean_up();
   
    return 0;   
}

---

Help please! :)

I immediately saw that apply_surface() doesn't give any proper return value. Start there.

I don't know what you mean? Why should it return something? :)

Because you now declare a return type, namely SDL_Surface*. The fact that you don't have a return statements make assignments such as this undefined:

Code:

---

up = apply_surface( 10, 0, piece, screen );

---

And undefined behaviour is bad.

Just because something compiles doesn't mean it's properly done. Even less so in C and C++ than in other languages.

Ok, i added "return 0;" to apply_surface() but it still doesn't work. The piece stays at it's position. Why? :o

Now i almost got it. It's just that the piece stays at the postion AND makes a new one. So i added SDL_FreeSurface( piece ); but now the program shuts down when i touch a button. Why? :o

Code:

---

//The headers
#include "SDL/SDL.h"
#include <string>

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The surfaces
SDL_Surface *background = NULL;
SDL_Surface *screen = NULL;
SDL_Surface *piece = NULL;

//The event structure
SDL_Event event;

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;
   
    //The optimized surface that will be used
    SDL_Surface* optimizedImage = NULL;
   
    //Load the image
    loadedImage = SDL_LoadBMP( filename.c_str() );
   
    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized surface
        optimizedImage = SDL_DisplayFormat( loadedImage );
       
        //Free the old surface
        SDL_FreeSurface( loadedImage );
    }
   
    //Return the optimized surface
    return optimizedImage;
}

SDL_Surface *apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL )
{
    //Holds offsets
    SDL_Rect offset;
   
    //Get offsets
    offset.x = x;
    offset.y = y;
   
    //Blit
    SDL_BlitSurface( source, clip, destination, &offset );
   
    return 0;
}

bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;   
    }
   
    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
   
    //If there was in error in setting up the screen
    if( screen == NULL )
    {
        return false;   
    }
   
    //Set the window caption
    SDL_WM_SetCaption( "Walk-around-game", NULL );
   
    //If everything initialized fine
    return true;
}

bool load_files()
{
    //Load the background image
    background = load_image( "bg.bmp" );
    piece = load_image( "piece.bmp" );
   
    //If there was a problem in loading the background
    if( background == NULL )
    {
        return false;   
    }
   
    //If there was a problem in loading the background
    if( piece == NULL )
    {
        return false;   
    }
   
    //If everything loaded fine
    return true;
}

void clean_up()
{
    //Free the surfaces
    SDL_FreeSurface( background );
    SDL_FreeSurface( piece );
   
    //Quit SDL
    SDL_Quit();
}

int main( int argc, char* args[] )
{
    int x = 50;
    int y = 50;
    //Quit flag
    bool quit = false;
   
    //Initialize
    if( init() == false )
    {
        return 1;
    }
   
    //Load the files
    if( load_files() == false )
    {
        return 1;
    }
   
    //Apply the piece
    apply_surface( x, y, piece, screen );
   
    //Apply the background
    apply_surface( 0, 0, background, screen );
   
    //While the user hasn't quit
    while( quit == false )
    {
        //If there's an event to handle
        if( SDL_PollEvent( &event ) )
        {
            //If a key was pressed
            if( event.type == SDL_KEYDOWN )
            {
                //Set the proper holder surface
                switch( event.key.keysym.sym )
                {
                    case SDLK_UP: x = x - 10; SDL_FreeSurface( piece ); apply_surface( y, x, piece, screen ); break;
                    case SDLK_DOWN: x = x + 10; SDL_FreeSurface( piece ); apply_surface( y, x, piece, screen ); break;
                    case SDLK_LEFT: y = y - 10; SDL_FreeSurface( piece ); apply_surface( y, x, piece, screen ); break;
                    case SDLK_RIGHT: y = y + 10; SDL_FreeSurface( piece ); apply_surface( y, x, piece, screen ); break;   
                }
            }
           
            //If the user has Xed out the window
            else if( event.type == SDL_QUIT )
            {
                //Quit the program
                quit = true;
            }
        }
   
        //Update the screen
        if( SDL_Flip( screen ) == -1 )
        {
            return 1;   
        }
    }
       
    //Clean up
    clean_up();
   
    return 0;   
}

---

Hmm... Anyone? :(

Weird... Anyone? :rolleyes:

You call SDL_FreeSurface once, once you're done with it. You can't do anything with the surface after it has been freed with this function. You can't free it again and you certainly can't access it again (both of which could happen if you press a key).

If you get rid of the SDL_FreeSurface calls in your switch statement, it will be closer to working.

BTW, the term for that kind of crash is a "segmentation fault" or a "seg fault".

Yeah, i know that. But it doesn't remove the old pic. How can i remove the old pic? OR even better, change the pic's position.

Helpneeded.please.com :) pleeeeeease :D

1. You need to read a book on beginner graphics
2. You need to 'blank' the sprite or start with a fresh background each frame

SDL_FillRect() with a NULL parameter for the rect does what you are looking for: http://docs.mandragor.org/files/Comm...lfillrect.html

Yeeeah! Now almost all works...

But if the user holds down a key, it stops after 1 step and if the user aint pressing any key, i wanna show piece.bmp!

Code:

Code:

---

//The headers
#include "SDL/SDL.h"
#include <string>
#include <iostream>

using namespace std;

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The surfaces
SDL_Surface *background = NULL;
SDL_Surface *screen = NULL;
SDL_Surface *piece = NULL;

//The event structure
SDL_Event event;

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;
   
    //The optimized surface that will be used
    SDL_Surface* optimizedImage = NULL;
   
    //Load the image
    loadedImage = SDL_LoadBMP( filename.c_str() );
   
    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized surface
        optimizedImage = SDL_DisplayFormat( loadedImage );
       
        //Free the old surface
        SDL_FreeSurface( loadedImage );
    }
   
    //Return the optimized surface
    return optimizedImage;
}

SDL_Surface *apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL )
{
    //Holds offsets
    SDL_Rect offset;
   
    //Get offsets
    offset.x = x;
    offset.y = y;
   
    //Blit
    SDL_BlitSurface( source, clip, destination, &offset );
   
    return 0;
}

bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;   
    }
   
    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
   
    //If there was in error in setting up the screen
    if( screen == NULL )
    {
        return false;   
    }
   
    //Set the window caption
    SDL_WM_SetCaption( "Walk-around-game", NULL );
   
    //If everything initialized fine
    return true;
}

bool load_files()
{
    //Load the background image
    background = load_image( "bg.bmp" );
    piece = load_image( "piece.bmp" );
   
    //If there was a problem in loading the background
    if( background == NULL )
    {
        return false;   
    }
   
    //If there was a problem in loading the background
    if( piece == NULL )
    {
        return false;   
    }
   
    //If everything loaded fine
    return true;
}

int clean_up()
{
    //Free the surfaces
    SDL_FreeSurface( background );
    SDL_FreeSurface( piece );
   
    //Quit SDL
    SDL_Quit();
   
    return 0;
}

int main( int argc, char* args[] )
{
    int x = 50;
    int y = 50;
   
    //Quit flag
    bool quit = false;
   
    //Initialize
    if( init() == false )
    {
        return 1;
    }
   
    //Load the files
    if( load_files() == false )
    {
        return 1;
    }
   
    //Apply the piece
    apply_surface( x, y, piece, screen );
   
    //Apply the background
    apply_surface( 0, 0, background, screen );
   
    //While the user hasn't quit
    while( quit == false )
    {
        //If there's an event to handle
        if( SDL_PollEvent( &event ) )
        {
            //If a key was pressed
            if( event.type == SDL_KEYDOWN )
            {
                //Set the proper holder surface
                switch( event.key.keysym.sym )
                {
                    case SDLK_UP:
                        x = x - 10;
                        SDL_FillRect( screen, NULL, NULL);
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-up.bmp" );
                        apply_surface( y, x, piece, screen );
                        break;
                       
                    case SDLK_DOWN:
                        x = x + 10;
                        SDL_FillRect( screen, NULL, NULL );
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-down.bmp" );
                        apply_surface( y, x, piece, screen );
                        break;
                       
                    case SDLK_LEFT:
                        y = y - 10;
                        SDL_FillRect( screen, NULL, NULL );
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-left.bmp" );
                        apply_surface( y, x, piece, screen );
                        break;
                       
                    case SDLK_RIGHT:
                        y = y + 10;
                        SDL_FillRect( screen, NULL, NULL );
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-right.bmp" );
                        apply_surface( y, x, piece, screen );
                        break;
                       
                    case SDLK_ESCAPE:
                        quit = true;
                        break;   
                }
            }
           
            }   
            //If the user has Xed out the window
            else if( event.type == SDL_QUIT )
            {
                //Quit the program
                quit = true;
            }
   
        //Update the screen
        if( SDL_Flip( screen ) == -1 )
        {
            return 1;   
        }
    }
       
       
    //Clean up
    clean_up();
   
    return 0;   
}

---

Please help me!

Pllllllllease..... :P

I've added and changed some code... I tried to get the non-press?-show-piece.png-thing, but it fails. So i need help please. And 1 more thing, when i compile and drive it works but if i double-click at the .exe file on my hardrive, it doesn't. It pops up and closes.

Code:

---

//The headers
#include "SDL/SDL.h"
#include "SDL/SDL_image.h"
#include <string>
#include <iostream>

using namespace std;

//Screen attributes
const int SCREEN_WIDTH = 640;
const int SCREEN_HEIGHT = 480;
const int SCREEN_BPP = 32;

//The surfaces
SDL_Surface *background = NULL;
SDL_Surface *screen = NULL;
SDL_Surface *piece = NULL;

//The event structure
SDL_Event event;

SDL_Surface *load_image( std::string filename )
{
    //The image that's loaded
    SDL_Surface* loadedImage = NULL;
   
    //The optimized surface that will be used
    SDL_Surface* optimizedImage = NULL;
   
    //Load the image
    loadedImage = IMG_Load( filename.c_str() );
   
    //If the image loaded
    if( loadedImage != NULL )
    {
        //Create an optimized surface
        optimizedImage = SDL_DisplayFormat( loadedImage );
       
        //Free the old surface
        SDL_FreeSurface( loadedImage );
       
       
        //If the image was optimized just fine
        if( optimizedImage != NULL )
        {
            //Map the color key
            Uint32 colorkey = SDL_MapRGB( optimizedImage->format, 0xFA, 0xF9, 0x7C );
           
            //Set all pixels of color R 0, G 0xFF, B 0xFF to be transparent
            SDL_SetColorKey( optimizedImage, SDL_RLEACCEL | SDL_SRCCOLORKEY, colorkey );
        }
    }
   
    //Return the optimized surface
    return optimizedImage;
}

SDL_Surface *apply_surface( int x, int y, SDL_Surface* source, SDL_Surface* destination, SDL_Rect* clip = NULL )
{
    //Holds offsets
    SDL_Rect offset;
   
    //Get offsets
    offset.x = x;
    offset.y = y;
   
    //Blit
    SDL_BlitSurface( source, clip, destination, &offset );
   
    return 0;
}

bool init()
{
    //Initialize all SDL subsystems
    if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 )
    {
        return false;   
    }
   
    //Set up the screen
    screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE );
   
    //If there was in error in setting up the screen
    if( screen == NULL )
    {
        return false;   
    }
   
    //Set the window caption
    SDL_WM_SetCaption( "Walk-around-game", NULL );
   
    //If everything initialized fine
    return true;
}

bool load_files()
{
    //Load the background image
    background = load_image( "bg.jpg" );
    piece = load_image( "howto.png" );
   
    //If there was a problem in loading the background
    if( background == NULL )
    {
        return false;   
    }
   
    //If there was a problem in loading the background
    if( piece == NULL )
    {
        return false;   
    }
   
    //If everything loaded fine
    return true;
}

int clean_up()
{
    //Free the surfaces
    SDL_FreeSurface( background );
    SDL_FreeSurface( piece );
   
    //Quit SDL
    SDL_Quit();
   
    return 0;
}

int main( int argc, char* args[] )
{
    //The pieces coordinates
    int x = 200;
    int y = 200;
   
    //Keydown flag
    bool keydown = false;
   
    //Quit flag
    bool quit = false;
   
    //Initialize
    if( init() == false )
    {
        return 1;
    }
   
    //Load the files
    if( load_files() == false )
    {
        return 1;
    }
   
    //Apply the background
    apply_surface( 0, 0, background, screen );
   
    //Apply the piece
    apply_surface( 70, 178, piece, screen );
   
    //While the user hasn't quit
    while( quit == false )
    {
        //If there's an event to handle
        if( SDL_PollEvent( &event ) )
        {
            //If a key was pressed
            if( event.type == SDL_KEYDOWN )
            {
                //Set the proper holder surface
                switch( event.key.keysym.sym )
                {                     
                    case SDLK_LEFT:
                        x = x - 10;
                        SDL_FillRect( screen, NULL, NULL );
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-left.png" );
                        apply_surface( x, y, piece, screen );
                        break;
                       
                    case SDLK_RIGHT:
                        x = x + 10;
                        SDL_FillRect( screen, NULL, NULL );
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-right.png" );
                        apply_surface( x, y, piece, screen );
                        break;
                       
                    case SDLK_ESCAPE:
                        quit = true;
                        break;   
                }
            }
           
            }   
            //If the user has Xed out the window
            else if( event.type == SDL_QUIT )
            {
                //Quit the program
                quit = true;
            }
   
        //Update the screen
        if( SDL_Flip( screen ) == -1 )
        {
            return 1;   
        }
    }
       
       
    //Clean up
    clean_up();
   
    return 0;   
}

---

Help me! I would be glad even for the smallest notice!

I'm not quite sure what you mean in your most recent post when you say "but it fails". For the issue of only moving once when you press a key, my understanding (I'm new to C++ and SDL too) is that SDL only generates events when a key changes state.

So when you press a key down, one event is generated. Another event will not be generated for that key until it is released again - even if you hold the key for an hour there will be no more events until it it released.

What is the solution for this? You need to use a flag variable to determine whether the key is currently pressed down or not. When you detect a key press, make this value true. When you detect a key release, make it false. Then in a separate part of your code you can check if that flag value is true, and if it is, perform your moves.

Yeah! I solved one problem or two now! :) Hold down the key, won't work. Why?! :o

Code:

---

    //While the user hasn't quit
    while( quit == false )
    { 
        //If there's an event to handle
        if( SDL_PollEvent( &event ) )
        {
            //If a key was pressed
            if( event.type == SDL_KEYDOWN )
            {
                //Set the proper holder surface
                switch( event.key.keysym.sym )
                {                     
                    case SDLK_LEFT:
                        left = true;
                        break;
                       
                    case SDLK_RIGHT:
                        right = true;
                        break;
                       
                    case SDLK_ESCAPE:
                        quit = true;
                        break;   
                }
            }
           
            //Check if the right is pressed
            while (right == true)
            {
                        x = x + 10;
                        SDL_FillRect( screen, NULL, NULL );
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-right.png" );
                        apply_surface( x, y, piece, screen );
            }
           
            //Check if the left is pressed
            while (left == true)
            {
                        x = x - 10;
                        SDL_FillRect( screen, NULL, NULL );
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-left.png" );
                        apply_surface( x, y, piece, screen );
            }
           
            }   
            //If the user has Xed out the window
            else if( event.type == SDL_QUIT )
            {
                //Quit the program
                quit = true;
            }
   
        //Update the screen
        if( SDL_Flip( screen ) == -1 )
        {
            return 1;   
        }
    }

---

This is a part of the code. Why does it fail? The thing that happen is that nothing happens. When i press a key, i want howto.png to disappear. I know how to do this, but nothing happens. Please explain why1

Changed my problem :)

Quote:

---

When i press a key, i want howto.png to disappear.

---

In order to do this, you need to paint over the area where howto.png was located with SDL_FillRect(), and then call SDL_UpdateRect() to make the changes visible (after making any other changes you might want to the screen). I don't see any calls to SDL_UpdateRect() in your code, but perhaps I'm missing something. (Or perhaps SDL_Flip() works as well, I don't know.)

ok i dont think this will help much but lazyfoo has some great sdl tutorials ill find the link and post it but if u cant wait for that just google lazyfoo it goes through most of the sdl routines u would need i think your problem might be thw while loops try this?

Code:

---

  //Check if the right is pressed
            if (right == true)
            {
                        x = x + 10;
                        SDL_FillRect( screen, NULL, NULL );
                        apply_surface( 0, 0, background, screen );
                        piece = load_image( "piece-right.png" );
                        apply_surface( x, y, piece, screen );
            }

---

this way it will loop past this every time instead of relooping just this part
so every time it loops past it will x+= 10;
at least i think it will :)

im not 100% because i havent used sdl or programmed in a while now but
i think sdl_flip() acts as a buffer and stores the next screen ready to display
so if u load a black white screen onto the screen

Code:

---

      applysurface(0,0,blankscreen,screen);

---

blankscreen being a white screen the same size as the (screen)

then when u flip it will be blank