Question

For FPS calculation, I use some code I found on the web and it’s working well. However, I don’t really understand it. Here’s the function I use:

void computeFPS()
{
  numberOfFramesSinceLastComputation++;
  currentTime = glutGet(GLUT_ELAPSED_TIME);

  if(currentTime - timeSinceLastFPSComputation > 1000)
  {
    char fps[256];
    sprintf(fps, "FPS: %.2f", numberOfFramesSinceLastFPSComputation * 1000.0 / (currentTime . timeSinceLastFPSComputation));
    glutSetWindowTitle(fps);
    timeSinceLastFPSComputation = currentTime;
    numberOfFramesSinceLastComputation = 0;
  }
 }

My question is, how is the value that is calculated in the sprint call stored in the fps array, since I don’t really assign it.

Answer 1

This is not a question about OpenGL, but the C standard library. Reading the reference documentation of s(n)printf helps:

man s(n)printf: http://linux.die.net/man/3/sprintf

In short snprintf takes a pointer to a user supplied buffer and a format string and fills the buffer according to the format string and the values given in the additional parameters.

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Here’s my suggestion: If you have to ask about things like that, don’t tackle OpenGL yet. You need to be fluent in the use of pointers and buffers when it comes to supplying buffer object data and shader sources. If you plan on using C for this, get a book on C and thoroughly learn that first. And unlike C++ you can actually learn C to some good degree over the course of a few months.