SDL Double buffering on HW_SURFACE

Question

I dont understand why my SDL app wont set the DOUBLE_BUF as i'm asking;

Here is a short code, this, executed without arguments open a fullscreen window, 1024*768, in 32 BPP mode.

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

#include "main.h"

SDL_Surface *screen;
Main mainstruct;

void testModesInFormat(SDL_PixelFormat * format)
{

    SDL_Rect **modes;
    int i;

    printf("Available hardware accelerated, fullscreen modes in %d bpp:\n",
           format->BitsPerPixel);

    modes = SDL_ListModes(format, SDL_FULLSCREEN | SDL_HWSURFACE | SDL_DOUBLEBUF);

    // Check is there are any modes available
    if(modes == (SDL_Rect **) 0)
    {
        printf("\tNo modes available!\n");
        return;
    }

    // Check if our resolution is restricted
    if(modes == (SDL_Rect **) - 1)
    {
        printf("\tAll resolutions available.\n");
    }
    else
    {
        // Print valid modes
        for(i = 0; modes[i]; ++i)
            printf("\t%d x %d\n", modes[i]->w, modes[i]->h);
    }

    free(modes);

}

void testModes()
{
    SDL_PixelFormat format;
    format.BitsPerPixel = 16;
    testModesInFormat(&format);
    format.BitsPerPixel = 24;
    testModesInFormat(&format);
    format.BitsPerPixel = 32;
    testModesInFormat(&format);
}

int main(int argc, char *argv[])
{

    printf("Hello world!\n");
    Uint32 flags = SDL_DOUBLEBUF;
    int w, h, bpp;
    int i;
    int hw_mem = 1;
    w = 1024;
    h = 768;
    bpp = 32;

    mainstruct.full_screen = 1;

    if(SDL_Init(SDL_INIT_AUDIO | SDL_INIT_VIDEO) < 0)
    {
        fprintf(stderr, "Unable to init SDL: %s\n", SDL_GetError());
        exit(1);
    }
    atexit(SDL_Quit);

    for(i = 0; i < argc; i++)
    {
        if(!strcmp(argv[i], "--window"))
        {
            mainstruct.full_screen = 0;
        }
        else if(!strcmp(argv[i], "--no-hardwarememory") || !strcmp(argv[i], "-nohw"))
        {
            hw_mem = 0;
        }
        else if(!strcmp(argv[i], "--test") || !strcmp(argv[i], "-t"))
        {
            testModes();
            exit(0);
        }
    }

    if(hw_mem)
    {
        flags |= SDL_HWSURFACE;
    }
    else
    {
        flags |= SDL_SWSURFACE;
    }
    if(mainstruct.full_screen)
    {
        flags |= SDL_FULLSCREEN;
    }
    fprintf(stderr, "Attempting to set %dx%dx%d video mode.\n", w, h, bpp);
    fflush(stderr);
    screen = SDL_SetVideoMode(w, h, bpp, flags);
    if(screen == NULL)
    {
        fprintf(stderr, "Unable to set %dx%dx%d video: %s\n", w, h, bpp,
                SDL_GetError());
        exit(1);
    }
    fprintf(stderr, "Success:\n");
    fprintf(stderr, "\tSDL_HWSURFACE =%s\n",
            (screen->flags & SDL_HWSURFACE ? "true" : "false"));
    fprintf(stderr, "\tSDL_FULLSCREEN=%s\n",
            (screen->flags & SDL_FULLSCREEN ? "true" : "false"));
    fprintf(stderr, "\tSDL_DOUBLEBUF =%s\n",
            (screen->flags & SDL_DOUBLEBUF ? "true" : "false"));
    fprintf(stderr, "\tw=%d h=%d bpp=%d pitch=%d\n", screen->w, screen->h,
            screen->format->BitsPerPixel, screen->pitch);
    fflush(stderr);
    return 0;
}

As you see, args are; --window disable fullscreen --no-hardwarememory set SDL_SWSURFACE in place of SDL_HWSURFACE --test call the testModes() function

So here are my output;

Without arguments ( flags are "SDL_DOUBLEBUF | SDL_HWSURFACE | SDL_FULLSCREEN" ) I get this;

Attempting to set 1024x768x32 video mode.
Success:
    SDL_HWSURFACE =false
    SDL_FULLSCREEN=true
    SDL_DOUBLEBUF =false
    w=1024 h=768 bpp=32 pitch=4096

With the --test arg, i get this:

Available hardware accelerated, fullscreen modes in 16 bpp:
    1920 x 1080
    1768 x 992
    1680 x 1050
    [...]
    640 x 480
Available hardware accelerated, fullscreen modes in 24 bpp:
    No modes available!
Available hardware accelerated, fullscreen modes in 32 bpp:
    1920 x 1080
    1768 x 992
    1680 x 1050
    [...]
    640 x 480

For thoses who want to compile this, here is the main.h

#ifndef MAIN_H
#define MAIN_H
#include "SDL.h"
#include "SDL_thread.h"

typedef struct _main {
  int full_screen;
} Main;
extern Main mainstruct;

#endif

So i want to understand why DOUBLE_BUF does not work, in 32bpp fullscreen .. Some ideas ?

Answer 1

If you're using Windows, the problem is probably in:

SDL 1.2.10 Release Notes
...
Windows Notes 
  The "windib" video driver is the default now, to prevent problems with 
  certain laptops, 64-bit Windows, and Windows Vista. The DirectX driver is 
  still available, and can be selected by setting the environment variable
  SDL_VIDEODRIVER to "directx".
...

http://www.libsdl.org/release/changes.html

After adding SDL_putenv("SDL_VIDEODRIVER=directx"); to your code the programm prints out:

Attempting to set 1024x768x32 video mode.
Success:
    SDL_HWSURFACE =true
    SDL_FULLSCREEN=true
    SDL_DOUBLEBUF =true
    w=1024 h=768 bpp=32 pitch=4096