sdl osx eclipse c++ display error - c++

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();
}