sdl osx eclipse c ++显示错误

Question

I've got a problem in running SDL app in eclipse under osx.

#include <SDL/SDL_opengl.h>
#include <SDL/SDL.h>
#include <SDL_ttf/SDL_ttf.h>
#include <SDL_image/SDL_image.h>
#include <iostream.h>

int main(int argc, char* argv[]){
    int error;
    error = SDL_Init(SDL_INIT_EVERYTHING);
    std::cout << "error " << error << std::endl;
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 8);
    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);

    Uint32 flags;

    flags = SDL_OPENGL | SDL_HWSURFACE | SDL_HWPALETTE| SDL_DOUBLEBUF ;
    drawContext = SDL_SetVideoMode(1024, 768, 16, flags);

    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0f, 1024, 768, 0.0f, 0.0f, 1000.0f);

    glMatrixMode(GL_MODELVIEW);

    while(true){
        glFinish();
        SDL_GL_SwapBuffers();
    }
}

this get weired output.

This only happens using the

SDL_OPENGL

flag.

Any ideas?

Answer 1

You never bother to clear the default framebuffer to a known value and the GL implementation isn't required to give you a cleared buffer.

OpenGL 4.3 spec , page 254, paragraph 1 (emphasis mine):

The default framebuffer is initially used as the draw and read framebuffer, and the initial state of all provided bitplanes is undefined . The format and encoding of buffers in the draw and read framebuffers can be queried as described in section 9.2.3.

Clear the framebuffer sometime before you swap:

while(true)
{
    glClear( GL_COLOR_BUFFER_BIT );

    // draw stuff

    SDL_GL_SwapBuffers();
}