Thread: SDL C Problem

I've just recently started fooling with SDL, yet I'm having troubles.

Some Info:
- compiling under mingw32
- using C::B and DevC++ as my IDE of choice
- 32-bit Vista, newest service pack updated
- nVidia GT 130M Graphic Card, newest drivers updated

First of all, whenever i try to compile my code under, DevCPP I'm getting a BSoD, however C::B doesnt seem to have this problem. Anyone know or heard what might be the issue?

Second, this is a basic code that is suppose to blink 3 times an image on the screen, when i compile and run the code however, i just get black screen. Ideas?

Code:

#include <stdio.h>
#include <stdlib.h>
#include "SDL/SDL.h"

#define TRUE 0
#define FALSE 1
#define SCREEN_WIDTH 640
#define SCREEN_HEIGHT 480
#define SCREEN_BPP 32

SDL_Surface *image = NULL;
SDL_Surface *screen = NULL;

signed int initEngine();
void quitEngine();
void updateScreen();
SDL_Surface* loadImage(char* filename);
void applySurface(int x, int y, SDL_Surface* source, SDL_Surface* destination);

int main (int argc, char* args[])
{
    initEngine();
    image = loadImage("1.bmp");
    applySurface(40, 40, image, screen);
        applySurface(100, 100, image, screen);
            applySurface(200, 200, image, screen);
    updateScreen();
    SDL_Delay(2000);
    quitEngine();

    return TRUE;
}

signed int initEngine()
{
    if(SDL_Init(SDL_INIT_EVERYTHING) == -1)
    {
        return FALSE;
    }

    screen = SDL_SetVideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE);

    if(screen == NULL)
    {
        return FALSE;
    }
    SDL_WM_SetCaption("Engine", NULL);
    return TRUE;
}

void quitEngine()
{
    SDL_FreeSurface(image);
    SDL_FreeSurface(screen);
    SDL_Quit();
}

void updateScreen()
{
    SDL_Flip(screen);
}

SDL_Surface* loadImage(char* filename)
{
    SDL_Surface* loadedImage = NULL;
    SDL_Surface* optimizedImage = NULL;

    loadedImage = SDL_LoadBMP(&filename);

        if(loadedImage != NULL)
        {
            optimizedImage = SDL_DisplayFormat(loadedImage);
            SDL_FreeSurface(loadedImage);
        }
    return optimizedImage;
}

void applySurface(int x, int y, SDL_Surface* source, SDL_Surface* destination)
{
    SDL_Rect offset;

    offset.x = x;
    offset.y = y;
    SDL_BlitSurface(source, NULL, destination, &offset);
}

Cheers,

You don't check the return of initEngine, so you may not even have SDL loaded or available at all - that's before you even BEGIN to draw to the screen using it. However, you blithely ignore that fact and carry on anyway.

Similarly for loadImage - the image may not even exist or be where the program expects it, or completely corrupt, but it carries along merrily anyway, trying to blit it to the screen.

You should also be checking return values in applySurface. (EDIT: I take back what I said about dstrect in an earlier revision of this post, though, because I was working on something else very similar at the time and it doesn't apply for your code).

That's honestly just from a 20-second skim to see what the program does. I suspect there may be other problems too.

P.S. I use a 130M too, on XP though, and I prefer Eclipse for my C-and-SDL projects. Specifically, I use Wascana, which bundles a pre-configured version of MinGW into an Eclipse install. You'll probably want to update both the version of MinGW in that environment, AND the version of Eclipse too after installation (I use Helios, dunno if the newer versions work with Wascana). That said, if something BSoD's on you, ever, you should really find an alternative immediately. It's not suggestive of good code and you don't want to spend your life wondering if your program's crashed or your OS or your IDE.

Apart from the other observations it may be that your code is actually ' working ' You call applySurface() three times, and then updateScreen() once, followed by your SDL pause. It is unsurprising in this case that you are going to see a black screen, as it has completed before you can see it.

Try just displaying the image once, the pause is not neccesary unless you put your code in a loop. Like with a counter and switch statement.

It is clear that you have been following the Lazy Foo tutorials, they are good If you are willing to do more than copy paste and hope, He has in my opinion put in a huge amount of work to publish useful tuts, and continues to try and bug hunt and improve them, certainly they helped me a lot, I would recommend you start from the easiest examples, get a grasp of what is going on then work from there.

is there a bool type in C ?

EDIT ahh, behind on the standards i am it seems

Originally Posted by rogster001

Apart from the other observations it may be that your code is actually ' working ' You call applySurface() three times, and then updateScreen() once, followed by your SDL pause. It is unsurprising in this case that you are going to see a black screen, as it has completed before you can see it.

This isn't entirely true. He blits three surfaces to different locations on the screen. Then he calls SDL_Flip (which actually just calls SDL_UpdateRect because he hasn't requested SDL_DOUBLEBUF surfaces). This will update the screen, and then the application will pause for 2 seconds and then quit. Although you might not see anything because of other problems, it's not necessary to call SDL_Flip every 60th of a second or whatever - it will just update the screen when called and not otherwise. If you dragged a window over the SDL window, it won't update the image, but so long as you don't do that, it should display the three images for 2 seconds before quitting.

The fact that it doesn't display ANYTHING is probably down to failing to check the returns - I bet the image isn't in the program directory or wherever the program is looking for it, for example, but in some subdirectory or in the source directory instead of where the final binary is run from. Even on the fastest of machines you should have at least seen the flicker of any SDL_Flip with blits pending.

Originally Posted by rogster001

is there a bool type in C ?

EDIT ahh, behind on the standards i am it seems

Indeed there is the obscure bool in stdbool but nobody uses it probably because most of the standard library has no use for it.

it should display the three images for 2 seconds before quitting.

after looking again i see this is true , but if the image was not present does SDL not output an error anyway? Regardless of return codes? I can't remember, its a long time since i used it.

Originally Posted by rogster001

after looking again i see this is true , but if the image was not present does SDL not output an error anyway? Regardless of return codes? I can't remember, its a long time since i used it.

No. Otherwise what would be the point of error codes.

SDL has SDL_GetError(). Programs are expected to catch poor return codes and print the result of SDL_GetError() to the user. Not all of them do and anything that isn't console-based (i.e. almost all SDL apps) won't see them anyway.

Personally, I check for returns and on failure jump to an error function that printf()'s SDL_GetError and also MessageBox's it (on Windows) if it's critical. At least then the user can do some diagnosis on what happened rather than being rudely thrown out of the program or experiencing symptoms like this.

Hell, most SDL programs I know even redirect stdout/stderr to files so that users aren't bothered by consoles popping up and the programmer can use them to aid diagnosis in the case of a program.