Question

我过去使用SDL和过剩（单独）没有太多问题，现在我想将SDL / opengl用于项目。当我调用第一个openGl函数时，无论我尝试使用哪个openGl函数，我都会遇到段错误。

我尝试过在网上找到的5个不同的示例程序。我尝试this SDLgears example from the sdl website只对源（SDL_GetKeyState - ＆gt; SDL_GetKeyboardState）进行了非常小的更改，但它也失败了。这让我觉得我的图书馆可能有问题吗？

以下是我的相关macports库：

libsdl-devel @1.3.0-5552_0 (active)
libsdl_mixer @1.2.11_3 (active)
mesa @7.8.2_2 (active)

虽然我不清楚-lGL是mesa还是系统库。

我尝试过的所有例子都归结为：

#include <SDL/SDL.h>
#include <SDL/SDL_opengl.h>

void
warn_if_fail(int sdl_ret)
{
    if (sdl_ret < 0)
      printf("opengl error: %s\n", SDL_GetError());
}

int main(int argc __attribute__((unused)), char* args[] __attribute__((unused)))
{
    // init sdl video
    SDL_Init(SDL_INIT_VIDEO);

    //print video info
    const SDL_VideoInfo* info = SDL_GetVideoInfo();
    printf("video card memory: %d\n",         info->video_mem);
    printf("current_w: %d, current_hh: %d\n", info->current_w, info->current_h);
    printf("bpp: %d\n",                       info->vfmt->BitsPerPixel);
    printf("hardware_available: %d\n",        info->hw_available);
    printf("blit_hw: %d\n",                   info->blit_hw );

    // set SDL_GL attributes
    warn_if_fail(  SDL_GL_SetAttribute(SDL_GL_RED_SIZE,      8)  );
    warn_if_fail(  SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE,     8)  );
    warn_if_fail(  SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE,    8)  );
    warn_if_fail(  SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE,    8)  );
    warn_if_fail(  SDL_GL_SetAttribute(SDL_GL_BUFFER_SIZE,  32)  );
    warn_if_fail(  SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER,  1)  );
    warn_if_fail(  SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE,   32)  );

    // set video mode
    SDL_Surface* screen;
    if ( (screen = SDL_SetVideoMode( 640, 480, 32, SDL_OPENGL) ) == NULL)
        printf("video error: %s\n", SDL_GetError());
    printf("\nSDL_SetVideoMode success!\n");

    // print some attributes to make sure they were set correctly
    int red, green, blue, doublebuf;
    SDL_GL_GetAttribute(SDL_GL_RED_SIZE, &red);
    SDL_GL_GetAttribute(SDL_GL_GREEN_SIZE, &green);
    SDL_GL_GetAttribute(SDL_GL_RED_SIZE, &blue);
    SDL_GL_GetAttribute(SDL_GL_DOUBLEBUFFER, &doublebuf);
    printf("red size, green size, blue size: <%d, %d, %d>\n", red, green, blue);
    printf("double buffered? %s\n\n", doublebuf == 1 ? "yes" : "no");

    // init openGl stuff
    printf("about to segfault\n");
    glViewport(0,0,640,480);
    printf("won't reach this message\n");

    // this also would have segfaulted
    // All openGl functions I've tried have segfaulted
    glClearColor(0, 0, 0, 0); 

    SDL_Quit();
    return 0;
}

生成文件：

PROJ = sdl_opengl_test
CXX=g++
Q = @

CPP_SRC = sdl_opengl_test.cpp
OBJ = $(CPP_SRC:.cpp=.o)

WARNINGFLAGS = -Wall -Wextra -Wshadow -Werror
INCLUDES = -I/opt/local/include
CPPFLAGS = $(WARNINGFLAGS) $(INCLUDES) -D_THREAD_SAFE

LDFLAGS  = -L/opt/local/lib -lSDL -lGL -lGLU

$(PROJ): $(OBJ)
    @echo LD $@
    $(Q)$(CXX) $(OBJ) $(LDFLAGS) -o $@

%.o : %.cpp
    @echo CXX $@
    $(Q)$(CXX) $(CPPFLAGS) -c $< -o $@

clean:
    rm -f $(PROJ)
    rm -f $(OBJ)

程序输出：

greg@pimptop ~/space/blaah (git)-[master] % ./sdl_opengl_test
video card memory: 0
current_w: 1680, current_hh: 1050
bpp: 32
hardware_available: 0
blit_hw: 0

SDL_SetVideoMode success!
red size, green size, blue size: <8, 8, 8>
double buffered? yes

about to segfault
[1]    37420 segmentation fault  ./sdl_opengl_test

gdb输出：

(gdb) run
Starting program: /Users/greg/space/blaah/sdl_opengl_test 
Reading symbols for shared libraries .++++++............................. done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done
video card memory: 0
current_w: 1680, current_hh: 1050
bpp: 32
hardware_available: 0
blit_hw: 0
Reading symbols for shared libraries . done
Reading symbols for shared libraries .. done
Reading symbols for shared libraries . done
Reading symbols for shared libraries . done

SDL_SetVideoMode success!
red size, green size, blue size: <8, 8, 8>
double buffered? yes

about to segfault

Program received signal EXC_BAD_ACCESS, Could not access memory.
Reason: KERN_INVALID_ADDRESS at address: 0x0000000000000000
0x0000000000000000 in ?? ()
(gdb) bt
#0  0x0000000000000000 in ?? ()
#1  0x0000000100000d55 in main (argc=1, args=0x7fff5fbff378) at sdl_opengl_test.cpp:50

谢谢

Answer 1

如果您的代码在第一次OpenGL调用中是segfaulting，那么<100> 100次中有99次，这是因为您的OpenGL上下文没有正确设置。

This似乎是一个很好的教程，从Mac上的OpenGL / SDL开始。但是，这是代码块，看起来你正在使用gcc（我认为......？）和shell而不是图形IDE。您可以尝试从SDL / OpenGL教程中复制粘贴确切的代码，看看它是否有效。如果没有，您知道它与您的标题/库有关。

我强烈建议做的是接受所有不必要的SDL调用并运行您可能提出的最基本的程序。但是，看起来你已经完成了这项工作。

关于我上面提到的标题/库的主题，我发现这是最可能的嫌疑人。我相信SDL的最新稳定版本是1.2，我注意到你使用的是1.3。你正在使用带有1.2 lib的1.3 lib？尝试用最新的稳定版本替换你提到的那三个库。

祝你好运！绝对评论，如果我说的没有帮助，你仍然遇到问题。

第一次opengl调用的sdl / opengl段错误（macbook pro / macports）

1 个答案: