I wrote a simple program that allows to move a character. And when I add the functions allowing the background scrolling, at runtime, the program displays a black screen and not the background scrolling.
And here is the program code:
#include <stdio.h>#include <stdlib.h>
#include <SDL/SDL.h>
#include <SDL/SDL_image.h>
#include <SDL/SDL_ttf.h>
#include "fonctions.h"
int main (int argc,char *args[])
{int game=1;
int collision=0,i=0;
int x=0,y=0;
SDL_Surface *screen=NULL;
SDL_Surface *back=NULL;
SDL_Surface *ennemi=NULL;
SDL_Event event;
SDL_Rect offset,offsetennemi;
SDL_Init(SDL_INIT_VIDEO);
back = IMG_Load(“background.bmp”);
ennemi = IMG_Load(“voiture0.bmp”);
screen = SDL_SetVideoMode(740,580,16,SDL_HWSURFACE | SDL_DOUBLEBUF);
SDL_WM_SetCaption(“jeu”,NULL);
offset.x=0;
offset.y=0;
int direction;
//sprites
SDL_Rect clip[3];
SDL_Surface *faces=NULL;
faces=IMG_Load(“mouvements.png”);
clip[0].x=64;
clip[0].y=19;
clip[0].w=83;
clip[0].h=133;
> clip[1].x=212;
> clip[1].y=19;
> clip[1].w=83;
> clip[1].h=133;
> clip[2].x=364;
> clip[2].y=19;
> clip[2].w=83;
> clip[2].h=133;
> offsetennemi.x=0;
> offsetennemi.y=0;
> SDL_Rect posback;
> posback.x=50;
> posback.y=50;
> SDL_BlitSurface(back,&posback,screen,&offset);
> //SDL_BlitSurface(ennemi,NULL,screen,&offsetennemi);
>
> SDL_Flip(screen);
> SDL_Delay(3000);
> while(game)
> {
> SDL_Flip(screen);
> while(SDL_PollEvent(&event)) {
> switch(event.type) {
> case SDL_QUIT:
> game=0;
> break;
> case SDL_KEYDOWN:
> {
> if (event.key.keysym.sym == SDLK_RIGHT)
> direction = 1;
> if (event.key.keysym.sym == SDLK_LEFT)
> direction= 2;
> }
> break;
> case SDL_KEYUP:
> direction=0;
> break;
> }
> }
>
>
> if(direction==1)
> {
> if(i==3)
> {i=0;}
> printf("%d\n",i );
> offsetennemi.x+=20;
> SDL_BlitSurface(back,&posback,screen,&offset);
> SDL_BlitSurface(faces,&clip[i],screen,&offsetennemi);
> SDL_Flip(screen);
> SDL_Delay(200);
> i++;
>
> }
> else if(direction==2)
> {
> if(i==3)
> {i=0;}
> printf("%d\n",i );
> offsetennemi.x-=20;
> SDL_BlitSurface(back,&posback,screen,&offset);
> SDL_BlitSurface(faces,&clip[i],screen,&offsetennemi);
> SDL_Flip(screen);
> i++;
> SDL_Delay(200);
> }
> if(offsetennemi.x==100)
> { offsetennemi.x-=20;
> SDL_BlitSurface(faces,&clip[i],screen,&offsetennemi);
>
> }SDL_Flip(screen);
> SDL_Delay(200);
> posback.x+=70;
> }
> }