SDL_GetTicks() troubles

markelo · 08-05-2004, 03:37 AM

Once again hitting on troubles.
SDL_GetTicks(); returns same time when I last called it very often.

This causes troubles that in my 3D program framerate jumps between 1000 and 55 ( real value )
Animations and self moving objects seems to move okay. But why so erraric framerates ?

I have something like this at the beginning ( global variables )

Uint32 newtime=0;

Uint32 oldtime=0;
Uint32 passedtime=0;

Then in my code
newtime=SDL_GetTicks();
passedtime=newtime-oldtime;
cout<<"Framerate="<<( float ) ( ( float ) passedtime / 1000.0f )<<endl;
oldtime=newtime;
updateScreen (); //Draws the scene.

My platform is A64 3000+ with nfoce3 board.
My kernel is Red hat 9 with custom build 2.6.7 kernel. SDL version is same as came with RH9.

Hko · 08-05-2004, 08:00 AM

Try something like this. It's complete SDL program with frame-delay, but it does not draw anything.
I use it as a starting piont for an SDL-program. I took the frame-delay function from Sam Lantinga's example SDL-program "aliens". See http://www.libsdl.org/projects/aliens/

Code:

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <time.h>

#include "SDL.h"

#define FRAMES_PER_SEC  50

SDL_Surface *screen;

void updatescreen (void)
{
     /* Draw your frame here */
}

void init (void)
{
     srand (time (NULL));
     if (SDL_Init (SDL_INIT_VIDEO) < 0) {
          fprintf (stderr, "Unable to init SDL: %s\n", SDL_GetError ());
          exit (1);
     }
     atexit (SDL_Quit);

     screen = SDL_SetVideoMode (640, 480, 16, SDL_SWSURFACE);
     if (screen == NULL) {
          fprintf (stderr, "Unable to set 640x480x16 video mode: %s\n",
                   SDL_GetError ());
          exit (1);
     }
}

void framedelay (void)
{
     static Uint32 next_tick = 0;
     Uint32 this_tick;

     this_tick = SDL_GetTicks ();
     if (this_tick < next_tick) {
          SDL_Delay (next_tick - this_tick);
     }
     next_tick = this_tick + (1000 / FRAMES_PER_SEC);
}


void run (void)
{
     int done;
     SDL_Event event;

     done = 0;
     while (1) {
          framedelay ();
          while (SDL_PollEvent (&event)) {
               switch (event.type) {
               case SDL_QUIT:
                    return;
               }
          }
          updatescreen ();
     }
}


int main (int argc, char *argv[])
{
     init ();
     updatescreen ();
     run ();
     return 0;
}

Compile and link with:

Code:

gcc -g -Wall `sdl-config --cflags` `sdl-config --libs` -o progname progname.c

markelo · 08-05-2004, 01:12 PM

Quote:

Originally posted by Hko
Try something like this. It's complete SDL program with frame-delay, but it does not draw anything.
I use it as a starting piont for an SDL-program. I took the frame-delay function from Sam Lantinga's example SDL-program "aliens". See http://www.libsdl.org/projects/aliens/

That code could be fine but I want to measure framerates in different situations like when there are lots of objects and when there are only few and so on.
Example code you posted restricts framerates to pass certain value and I don't want that.

So my real question is is this SDL_GetTicks() so erratic with high update rate or do I have an another problem ?