Sync problem

Hendrik · December 13, 2003, 12:47am

Hi there… i’ve some probs with the following code.

SDL_GL_SwapBuffers() doesn’t sync with the display refresh.

Are there any necessary tests that need to be done before setting up
sdl/gl, or did I miss something in my init function?

thanks in advance

–hendrik

OS: win2k
HW: Radeon 7000
DevC++

#include
#include <stdlib.h>
#include <SDL/SDL.h>
#ifdef WIN32
#include <windows.h>
#endif
#include <GL/gl.h>
#include <GL/glu.h>
using namespace std;

SDL_Surface * screen = NULL;

int init_sdl()
{
GLint gl_doublebuf;
gl_doublebuf = SDL_DOUBLEBUF;

    SDL_Init(SDL_INIT_VIDEO);
    atexit(SDL_Quit);
    SDL_GL_SetAttribute(SDL_GL_RED_SIZE, 5);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE, 6);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE, 5);
    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 16);
    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, gl_doublebuf);    
    screen = SDL_SetVideoMode(640,480,16,SDL_DOUBLEBUF | SDL_OPENGL | SDL_FULLSCREEN);
    if(!screen)
    {
        fprintf(stderr,"failed to setup sdl");
        return -1;
    }
    glDisable(GL_DEPTH_TEST);
    glDisable(GL_CULL_FACE);
    glViewport(0, 0, screen->w, screen->h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, 640, 480, 0, -1.0, 1.0);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glTranslatef(0.0f, 0.0f, 0.0f);

}

void render(int x,int y)
{
glClearColor (0.0f, 0.0f, 0.0f, 0.0f);
glClear (GL_COLOR_BUFFER_BIT);

glBegin(GL_QUADS);
glColor4ub(255, 255, 255, 255);
glVertex2f(x, y);
glVertex2f(x+50, y);
glVertex2f(x+50, y+50);
glVertex2f(x, y+50);
glEnd();

}

int main(int argc, char *argv[])
{
int quit = 0;
int i=0;
SDL_Event event;
Uint8 *keys;
int x,y,xs,ys;
int st,et,fc;

init_sdl();

x = 0; y = 0; xs = 2; ys = 1;

keys = SDL_GetKeyState(&i);
st = SDL_GetTicks();
fc=0;
while(!quit)
{
            while(SDL_PollEvent(&event))
            {
                    if(keys[SDLK_ESCAPE])
                    {
                            quit = 1;
                            break;
                    }
            }
            x=x+xs;
            y=y+ys;
            if(x<0 || x>640-50) xs=-xs;
            if(y<0 || y>480-50) ys=-ys;
            render(x,y);
            SDL_GL_SwapBuffers();
            fc++;
}

et = (SDL_GetTicks() - st)/1000;
fprintf(stdout, "fps: %.2f | time: %d | frames: %d\n", (float)((float)fc/(float)et), et, fc);

return 0;

}

Bob_Pendleton · December 19, 2003, 11:29am

Hi there… i’ve some probs with the following code.

SDL_GL_SwapBuffers() doesn’t sync with the display refresh.

Are there any necessary tests that need to be done before setting up
sdl/gl, or did I miss something in my init function?

Some drivers do not sync with vertical retrace. You can usually get
around that by setting an environment variable or by setting a flag
through the drivers GUI. But, in general, you can not count on the
driver to sync so you have to write you code so it works no matter what.

Take a look at
http://linux.oreillynet.com/pub/a/linux/2003/10/23/sdl_anim.html for
more information.

	Bob PendletonOn Sat, 2003-12-13 at 02:45, Hendrik wrote: