When I ask SDL for a hardware surface I don't get one

**scwizard** · 07-13-2008

So to test out SDL I tried compiling the hello world program here: http://cone3d.gamedev.net/cgi-bin/in...ls/gfxsdl/tut1

Made some changes for diagnostic reasons:

Code:

SDL_Surface *screen;
const SDL_VideoInfo* VideoInfo = SDL_GetVideoInfo();
SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
screen = SDL_SetVideoMode(640,480,32,SDL_HWSURFACE|SDL_DOUBLEBUF|SDL_FULLSCREEN);
printf("%u\n%u\n", screen->flags, VideoInfo->hw_available);

Now according to the output I'm not getting SDL is unable to make screen a double buffered hardware surface.

Is there something wrong with my computer that it won't give SDL a double buffered hardware surface when it asks for one? Or am I making an elementary mistake?

**g4j31a5** · 07-20-2008

Are you using Linux? If so then it's a normal thing. Linux's X system can't get a hardware surface. If not, then your graphics card doesn't support it.

**scwizard** · 07-21-2008

I'm running windows on a very new laptop. I also sent the program to my brother who ran it with the same result, and a few of my friends all running windows.

**dwks** · 07-22-2008

Presumably your laptop has 32-bit colour?

I'm not sure if the SDL_GL_SetAttribute call is affecting your code at all. What happens if you remove it?

Instead of checking if a hardware surface is available, why not check if you actually got one?

Code:

if((screen->flags & SDL_HWSURFACE) == 0)
{
    printf("Can't get hardware surface\n");
}

[BTW, you can get hardware surfaces under Linux if you don't use the X driver, apparently. http://www.linuxdevcenter.com/pub/a/.../sdl_anim.html

Selecting The Driver
The first change I had to make was to add some Linux specific code just before the call to SDL_Init():

#ifdef __linux__
putenv("SDL_VIDEODRIVER=dga");
#endifSDL checks the value of the SDL_VIDEODRIVER environment variable to decide which driver to use. To get hardware surfaces while running on Linux under X, you have to specify which driver to use. I've chosen the DGA driver because the default X11 driver does not support hardware surfaces. The SDL FAQ has more information about selecting drivers on Linux and Windows. There is also a detailed list of SDL environment variables and their use. The number of different drivers that you have to choose from is staggering and shows the range of applications for which SDL could be used.

]

**BobMcGee123** · 07-24-2008

It's a very new laptop? Where did you put the installation files for SDL? That sounds like it could be an improperly installed dll.

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