Thread: SDL + Keys

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!

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?!

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

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.)