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sdl help

Started by dan1088352 Oct 28, 2004 at 9:49 AM 15 replies 3.9k views

Original Post

Oct 28, 2004 at 9:49 AM


#include <stdio.h>
#include <stdlib.h>

#include <SDL/SDL.h>

SDL_Surface *screen;
SDL_Surface *back;
SDL_Surface *image;

int xpos=100,ypos=300;

void init(SDL_Surface *screen)
{
    SDL_Init(SDL_INIT_AUDIO|SDL_INIT_VIDEO);
    screen = SDL_SetVideoMode(800,600,32,SDL_HWSURFACE|SDL_DOUBLEBUF);
    back = SDL_LoadBMP("bg.bmp");
    image = SDL_LoadBMP("img.bmp");
    atexit(SDL_Quit);
}

void drawimg(SDL_Surface *screen, int x, int y, SDL_Surface *blitto)
{
    Uint8* keys;
    keys = SDL_GetKeyState(NULL);
    if ( keys[SDLK_UP] ) { y -= 1; }
    if ( keys[SDLK_DOWN] ) { y += 1; }
    if ( keys[SDLK_LEFT] ) { x -= 1; }
    if ( keys[SDLK_RIGHT] ) { x += 1; }


    
  SDL_Rect dest;
  dest.x = x;
  dest.y = y;
  SDL_BlitSurface(screen, NULL, blitto, &dest);
}


int drawIMG(SDL_Surface *img, int x, int y, int x2, int y2, int w, int h)
{
    SDL_Rect dest;
    dest.x=x;
    dest.y=y;
    SDL_Rect dest2;
    dest2.x=x2;
    dest2.y=y2;
    dest.w=w;
    dest2.h=h;
    SDL_BlitSurface(img,&dest,screen,&dest2);
}    

int drawit()
{ 
    drawimg(image,0,0,screen);
    drawIMG(back,xpos,ypos,xpos-2,ypos-2,132,132);
    SDL_Flip(screen);
}

int main(int argc, char *argv[])
{
    Uint8 *keys;
  init(screen);
  int done=0;
  while(done ==0)
  {
    SDL_Event event;

    while ( SDL_PollEvent(&event) )
    {
      if ( event.type == SDL_QUIT )  {  done = 1;  }

      if ( event.type == SDL_KEYDOWN )
      {
        if ( event.key.keysym.sym == SDLK_ESCAPE ) { done = 1; }
      }
    }
    
        keys = SDL_GetKeyState(NULL);
    if ( keys[SDLK_UP] ) { ypos -= 1; }
    if ( keys[SDLK_DOWN] ) { ypos += 1; }
    if ( keys[SDLK_LEFT] ) { xpos -= 1; }
    if ( keys[SDLK_RIGHT] ) { xpos += 1; }
    done = 0;
    drawit();
  }
  return 0;
}

the screen closes instantly, anyone know why?

Muppi

Oct 28, 2004 at 9:53 AM

Try checking the return of your inits and such.

if(SDL_Init(SDL_INIT_AUDIO|SDL_INIT_VIDEO) < 0){    cout << SDL_GetError();}

dan1088352

Author

dan1088352

Oct 28, 2004 at 12:37 PM

the init went fine, it still flashes on, displays nothing then goes. the images did load, I put a check on that.

dan1088352

Author

dan1088352

Oct 28, 2004 at 6:15 PM

stderr says

Fatal signal: Segmentation Fault (SDL Parachute Deployed)

Gaiiden

589

Gaiiden

Oct 28, 2004 at 8:31 PM

run the debugger or place some output points in the code to find out where the last line of execution is before the crash.

Boku San

Oct 28, 2004 at 8:37 PM

Ahhh...the joys of debugging. Anyway, I'm going to step through this and try and help out, I had a problem like this a little while ago, and I probably commented on it in one of my sources.

Hope I can help.

Boku San

Oct 28, 2004 at 8:47 PM

It looks like something is messing up right around your drawit() function...commenting out SDL_Flip(screen); has a very interesting effect.

For the lazy, the effect is that it doesn't crash, but instead draws a blank screen. I'd say something's wrong with your drawing code...what, are you doublebuffering?

Gaiiden

589

Gaiiden

Oct 29, 2004 at 3:09 AM

I've pointed this out before, and no one's contradicted me - yet. I also haven't tested it myself, but why does everyone always leave the w and h members of SDL_Rect uninitialized?

SDL_Rect dest;dest.x = x;dest.y = y;SDL_BlitSurface(screen, NULL, blitto, &dest);

I assume the assumption is that dest.w and dest.h will equal the width and height of the surface, but in reality they're prob initialized to some garbage that just happens to be bigger than the width and height of the surface. Thus the blit works - but at what cost? Drakkcon is doing the same thing and is also complaining about crashing.

PnP Bios

114

PnP Bios

Oct 29, 2004 at 7:55 AM

You would know right away if SDL supported hardware surface stretch blits...

cplus programmer

Oct 29, 2004 at 11:13 AM

#include <stdio.h>#include <stdlib.h>#include <SDL/SDL.h>SDL_Surface *screen;SDL_Surface *back;SDL_Surface *image;int xpos=100,ypos=300;void init(){    back = SDL_LoadBMP("back.bmp");    if(back == NULL)    {        printf("cant load back");    }        image = SDL_LoadBMP("ball.bmp");    if(image == NULL)    {        printf("cant load the image");    }        atexit(SDL_Quit);}void drawimg(SDL_Surface *screen, int x, int y,int w, int h, SDL_Surface *blitto){      SDL_Rect dest;  dest.x = x;  dest.y = y;  dest.h=h;  dest.y=y;  SDL_BlitSurface(screen, NULL, blitto, &dest);}int drawIMG(SDL_Surface *img, int x, int y,int x2, int y2, int w, int h){    SDL_Rect dest;    dest.x=x;    dest.y=y;    SDL_Rect dest2;    dest2.x=x2;    dest2.y=y2;    dest.w=w;    dest2.h=h;    SDL_BlitSurface(img,&dest,screen,&dest2);}    int drawit(){    xpos=xpos+1;    drawimg(image, 50, 50,xpos,xpos,back);    drawimg(back, 0, 0,800,600,screen);    SDL_Flip(screen);    SDL_Flip(back);}int main(int argc, char *argv[]){    if(SDL_Init(SDL_INIT_AUDIO|SDL_INIT_VIDEO) < 0){    printf("unable to init", SDL_GetError());}    screen = SDL_SetVideoMode(800,600,32,SDL_HWSURFACE|SDL_DOUBLEBUF);    if(screen == NULL)    {        printf("cant set video mode");    }        Uint8 *keys;  init();  drawimg(back, 0, 0,800,600,screen);  int done=0;  while(done ==0)  {    SDL_Event event;    while ( SDL_PollEvent(&event) )    {      if ( event.type == SDL_QUIT )  {  done = 1;  }      if ( event.type == SDL_KEYDOWN )      {        if ( event.key.keysym.sym == SDLK_ESCAPE ) { done = 1; }      }    }            keys = SDL_GetKeyState(NULL);    if ( keys[SDLK_UP] ) { ypos -= 1; }    if ( keys[SDLK_DOWN] ) { ypos += 1; }    if ( keys[SDLK_LEFT] ) { xpos -= 1; }    if ( keys[SDLK_RIGHT] ) { xpos += 1; }    done = 0;    drawit();  }  return 0;}

the image will drag and I have to go to the task manager to quit it, know why?

Gaiiden

589

Gaiiden

Oct 30, 2004 at 4:43 AM

You should only be calling SDL_Flip for the main surface. The program's not quitting because you're setting done back to 0 every game loop (look above the drawit() call)

Quote:
Original post by PnP Bios
You would know right away if SDL supported hardware surface stretch blits...

Whazzat?

PnP Bios

114

PnP Bios

Oct 30, 2004 at 7:29 AM

well, if the w and h were garbage, and you were using them as real parameters, you would get some funky looking blits, and you would be able to visibly see that your parameters were messed up.

I think...

cplus programmer

Oct 30, 2004 at 10:16 AM

I did, there wher some changes.

cplus programmer

Oct 30, 2004 at 10:33 AM

this is the code right now

#include <stdio.h>#include <stdlib.h>#include <SDL/SDL.h>SDL_Surface *screen;SDL_Surface *back;SDL_Surface *image;int xpos,ypos;void init(){    back = SDL_LoadBMP("back1.bmp");    if(back == NULL)    {        printf("cant load back");    }        image = SDL_LoadBMP("ball.bmp");    if(image == NULL)    {        printf("cant load the image");    }        atexit(SDL_Quit);}void drawimg(SDL_Surface *screen, int x, int y,int w, int h, SDL_Surface *blitto){   SDL_Rect dest;  dest.x = x;  dest.y = y;  dest.h=h;  dest.y=y;  SDL_BlitSurface(screen, NULL, blitto, &dest);}int hitwall(int xpos ,int ypos ,int wall1 , int wall2){    if(xpos>wall1)    {        xpos=0;    }    if(xpos<0)    {        xpos=800;    }    if(ypos>wall2)    {        ypos = 0;    }    if(ypos<0)    {        ypos = 600;    }}                    int drawIMG(SDL_Surface *img, int x, int y,int w, int h,int x2,int y2){    SDL_Rect dest;    dest.x=x;    dest.y=y;    SDL_Rect dest2;    dest2.x=x2;    dest2.y=y2;    dest.w=w;    dest2.h=h;    SDL_BlitSurface(img,&dest,screen,&dest2);}    int drawit(){    hitwall(xpos,ypos,800,600);    drawIMG(back, xpos-2, ypos-2, 52, 52, xpos-2, ypos-2);    drawimg(image, xpos, ypos,500,50,screen);    SDL_Flip(screen);}int main(int argc, char *argv[]){    if(SDL_Init(SDL_INIT_AUDIO|SDL_INIT_VIDEO) < 0){    printf("unable to init", SDL_GetError());}    screen = SDL_SetVideoMode(800,600,32,SDL_HWSURFACE|SDL_DOUBLEBUF);    if(screen == NULL)    {        printf("cant set video mode");    }        Uint8 *keys;  init();  int done=0;  while(done ==0)  {    SDL_Event event;    while ( SDL_PollEvent(&event) )    {      if ( event.type == SDL_QUIT )  {  done = 1;  }      if ( event.type == SDL_KEYDOWN )      {        if ( event.key.keysym.sym == SDLK_ESCAPE ) { done = 1; }      }    }            keys = SDL_GetKeyState(NULL);    if ( keys[SDLK_UP] ) { ypos -= 10; }    if ( keys[SDLK_DOWN] ) { ypos += 10; }    if ( keys[SDLK_LEFT] ) { xpos -= 10; }    if ( keys[SDLK_RIGHT] ) { xpos += 10; }    drawit();  }  return 0;}

it just drags now

Gaiiden

589

Gaiiden

Oct 30, 2004 at 11:53 PM

use this to clear the screen before you blit and flip

SDL_FillRect(screen, 0, 0);

cplus programmer

Oct 31, 2004 at 12:17 PM

thank you very much

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