SDL openGL issue, no openGL drawing seen - opengl

Question

I am using cygwin SDL 1.2.15 using the latest cygwin
Here is my code using SDL and openGL
#include <SDL/SDL.h>
#include <SDL/SDL_opengl.h>
#include <iostream>
size_t sx=600, sy=600, bpp=32;
void render(void) {
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glLoadIdentity(); // set location in front of camera
//glTranslated(0, 0, -10);
glBegin(GL_QUADS); // draw a square
glColor3d(1, 0, 0);
glVertex3d(-2, 2, 0);
glVertex3d( 2, 2, 0);
glVertex3d( 2, -2, 0);
glVertex3d(-2, -2, 0);
glEnd();
glFlush();
SDL_GL_SwapBuffers();
GLenum e;
while ((e =glGetError()) != GL_NO_ERROR)
std::cout<<"Error "<< e << std::endl;
}
int input(void) {
SDL_Event event;
while (SDL_PollEvent(&event))
if (event.type == SDL_QUIT || (event.type == SDL_KEYUP && event.key.keysym.sym == SDLK_ESCAPE)) return 0;
return 1;
}
and this is my main function
int main(int argc, char *argv[]) {
SDL_Surface *surf;
if (SDL_Init(SDL_INIT_EVERYTHING) != 0) return 0;
if (!(surf = SDL_SetVideoMode(sx, sy, bpp, SDL_OPENGL))) return 0;
glViewport(0, 0, sx, sy);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, (float)sx / (float)sy, 1.0, 100.0);
glMatrixMode(GL_MODELVIEW);
glClearColor(0, 0, 0, 1);
glClearDepth(1.0);
glEnable(GL_DEPTH_TEST);
GLenum e;
while ((e =glGetError()) != GL_NO_ERROR)
std::cout<<"Error "<< e << std::endl;
for (;;) {
if (!input()) break;
render();
SDL_Delay(10);
}
SDL_FreeSurface(surf);
SDL_Quit();
return 0;
}
it compiles with no error but when I run it only the window shows up and now openGL rectangle..

Answer 1

You have setup a near plane to one :
gluPerspective(45.0, (float)sx / (float)sy, 1.0/*near plane*/, 100.0);
Everything that is closer to the camera is clipped.
Your quad lies in plane z = 0. Try moving it a bit backward.
glBegin(GL_QUADS); // draw a square
glColor3d(1, 0, 0);
glVertex3d(-2, 2, 5);
glVertex3d( 2, 2, 5);
glVertex3d( 2, -2, 5);
glVertex3d(-2, -2, 5);
glEnd();
I don't remember if Z is facing the camera, so you might need negative Z value.
You also need to pay attention to face culling. It might be better to deactivate it to be sure ( glDisable( GL_CULL_FACE ))

Answer 2

Try changing the black color of the SDL window. Some times it renders the drawing with black color...may be this helps!