Simple particles example using the OpenVG Testbed

particles.c

// particles.c - Simple particles example using the OpenVG Testbed

// Installing & Running:
// 1. Download the OpenVG Testbed (https://github.com/ajstarks/openvg)
//
//   $ git clone https://github.com/ajstarks/openvg.git
//   $ cd openvg/client
//
// 2. Place a copy of this file (particles.c) in that directory
// 3. Add the following to the Makefile:
//
//   particles:	particles.c ../libshapes.o ../oglinit.o
//     gcc   -Wall -I/opt/vc/include -I/opt/vc/include/interface/vcos/pthreads -I.. -o particles particles.c ../libshapes.o ../oglinit.o -L/opt/vc/lib -lGLESv2 -ljpeg -O3
//
// 4. Compile and run
//
//   $ make particles
//   $ ./particles
//
// Usage: ./particles [OPTIONS]
//
// Options:
//  -t  show trails
//
//  -r  right-to-left only  (direction alternates by default)
//  -l  left-to-right only

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <fcntl.h>
#include <time.h>
#include "VG/openvg.h"
#include "VG/vgu.h"
#include "fontinfo.h"
#include "shapes.h"

// ~55 seems to be the limit before jankiness kicks in
#define NUM_PARTICLES 50 

typedef struct particle {
  int x, y;
  double vx, vy;
  int r, g, b;
  int radius;
} particle_t;

particle_t particles[ NUM_PARTICLES ];

int showTrails   = 0;
int directionRTL = 0;
int alternate    = 1;

// Initialize _all_ the particles
void initParticles(int w, int h) {
  int i;
  for ( i = 0; i < NUM_PARTICLES; i++ ) {
    particle_t* p = &particles[i];

    p->x = 0; 
    p->y = 0;  
    p->vx = (rand() % 30) + 30;
    p->vy = (rand() % 20) + 40;
    p->r = rand() % 256;
    p->g = rand() % 256;
    p->b = rand() % 256;
    p->radius = (rand() % 20) + 20;

    if ( directionRTL ) {
      p->vx *= -1;
      p->x = w;
    }
  }
}

void paintBG(int w, int h) {
  if ( !showTrails ) return Background( 0, 0, 0 );

  Fill( 0, 0, 0, 0.3 );
  Rect( 0, 0, w, h );
}

void draw(int w, int h) {
  int i;
  particle_t* p;

  paintBG(w, h);

  for ( i = 0; i < NUM_PARTICLES; i++ ) {
    p = &particles[i];
    
    Fill( p->r, p->g, p->b, 1.0 );
    Circle( p->x, p->y, p->radius );

    // Apply the velocity
    p->x += p->vx;
    p->y += p->vy;

    p->vx *= 0.98;
    if ( p->vy > 0 ) p->vy *= 0.97;
    
    // Gravity
    p->vy -= 0.5;

    // Stop particles leaving the canvas  
    if ( p->x < -50 )    p->x = w + 50;
    if ( p->x > w + 50 ) p->x = -50;
    
    // When particle reaches the bottom of screen reset velocity & start posn
    if ( p->y < - 50 ) {
      p->x = 0;
      p->y = 0;  
      p->vx = (rand() % 30) + 30;
      p->vy = (rand() % 20) + 40;
    
      if ( directionRTL ) {
        p->vx *= -1;
        p->x = w;
      }
    }
    
    if ( p->y > h + 50 ) p->y = -50;
  }
  
  End();
}

void setOptions(int argc, char** argv) {
  int i = argc;
  while ( i-- ) {
    char option = argv[i][1];

    if ( option == 't' ) {
      showTrails = 1;
      printf("Displaying trails\n");
    }

    // If r or l is set, disable alternation
    if ( option == 'r' || option == 'l' ) alternate = 0;

    // Set direction
    if ( option == 'r' ) {
      directionRTL = 1;
      printf("Displaying in right-to-left mode\n");
    }

    if ( option == 'l' ) {
      directionRTL = 0;
      printf("Displaying in left-to-right mode\n");
    }
  }
}

// Display Options
// -t  show trails
//
// Direction (alternates by default)
// -r  right-to-left
// -l  left-to-right
int main(int argc, char** argv) {
  srand( time(NULL) );

  setOptions(argc, argv);

  int w, h;
  init( &w, &h );
  initParticles( w, h );

  Start( w, h );

  int i = 0;
  while ( 1 ) {
    draw( w, h );
    
    // NOTE: Consider a `usleep()` in here to not tie up the CPU if you intend serious use

    // Change launch direction every 100 draws
    i++;
    if ( alternate && i == 100 ) {
      directionRTL = directionRTL ? 0 : 1;
      i = 0;
    }
  }
}

I'd like to distribute a C# translation of this as a part of https://bitbucket.org/grrussel/openvg/src - my C# wrapper around AJStarks OpenVG lib.

I'd like to add this to openvg distro. Ok?