Lazy Foo' Productions

Particle Engines

Last Updated 3/28/10
Particle engines are ways to create effects like fire, smoke, or in this case a trail of sparks. Here we're going to make a very simple particle engine to surround the dot in sparks.
class Particle { private: //Offsets int x, y; //Current frame of animation int frame; //Type of particle SDL_Surface *type; public: //Constructor Particle( int X, int Y ); //Shows the particle void show(); //Checks if particle is dead bool is_dead(); };
Particles are just little animations. We want to surround the dot with a bunch of little flashing sparks that look like this:
So we'll create a particle class and give the dot a bunch of particles.

These spark particles are real simple. They have offsets, a frame of animation and a surface.

In terms of functions they have a constructor, a function to show the spark and a function to check if the spark is still active.
//The dot class Dot { private: //The offsets int x, y; //The velocity of the dot int xVel, yVel; //The particles Particle *particles[ TOTAL_PARTICLES ]; public: //Initializes Dot(); //Cleans up particles ~Dot(); //Handles keypresses void handle_input(); //Moves the dot void move(); //Shows the particles void show_particles(); //Shows the dot void show(); };
Here we have our good friend the dot class revised to include the particles.
bool init() { //Initialize all SDL subsystems if( SDL_Init( SDL_INIT_EVERYTHING ) == -1 ) { return false; } //Set up the screen screen = SDL_SetVideoMode( SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_BPP, SDL_SWSURFACE ); //If there was an error in setting up the screen if( screen == NULL ) { return false; } //Set the window caption SDL_WM_SetCaption( "Particle Test", NULL ); //Seed random srand( SDL_GetTicks() ); //If everything initialized fine return true; }
Because we're going to need random numbers for our particle engine, we seed random with the current time (which is a common way to do it) in our initialization function.
Particle::Particle( int X, int Y ) { //Set offsets x = X - 5 + ( rand() % 25 ); y = Y - 5 + ( rand() % 25 ); //Initialize animation frame = rand() % 5; //Set type switch( rand() % 3 ) { case 0: type = red; break; case 1: type = green; break; case 2: type = blue; break; } }
Here's the constructor for our particle class.

The "X" and "Y" arguments are going to be the offsets of the dot. We take the arguments and put the particle in a random place around the dot.

Then we initialize the animation a random number from 0 to 4. This is because we want the particles to animate asynchronously.

Then we set the surface type to be the red, green, or blue particle surface. This is also done at random.
void Particle::show() { //Show image apply_surface( x, y, type, screen ); //Show shimmer if( frame % 2 == 0 ) { apply_surface( x, y, shimmer, screen ); } //Animate frame++; }
Here is the show() function for our sparks.

All we do is show our surface then if the frame is divisible by 2 we show the shimmer surface on top of red, green or blue surface. The shimmer surface is just semitransparent white surface. The result will have the particles doing a flashing animation.
bool Particle::is_dead() { if( frame > 10 ) { return true; } return false; }
Here we have a function to check if a particle is dead or not.

A particle is considered dead after it animates for 10 frames.
Dot::Dot() { //Initialize the offsets x = 0; y = 0; //Initialize the velocity xVel = 0; yVel = 0; //Initialize particles for( int p = 0; p < TOTAL_PARTICLES; p++ ) { particles[ p ] = new Particle( x, y ); } } Dot::~Dot() { //Delete particles for( int p = 0; p < TOTAL_PARTICLES; p++ ) { delete particles[ p ]; } }
Here are the dot's constructor and destructor. The only changes to the dot class made here is that we generate particles in the constructor and get rid of them in the destructor.
void Dot::show() { //Show the dot apply_surface( x, y, dot, screen ); //Show the particles show_particles(); }
Here you can see we altered the dot's show() function to show the particles.
void Dot::show_particles() { //Go through particles for( int p = 0; p < TOTAL_PARTICLES; p++ ) { //Delete and replace dead particles if( particles[ p ]->is_dead() == true ) { delete particles[ p ]; particles[ p ] = new Particle( x, y ); } } //Show particles for( int p = 0; p < TOTAL_PARTICLES; p++ ) { particles[ p ]->show(); } }
When we show the particles we first go through them and remove and replace any dead particles.

After any dead particles are replaced we show the particles on top of the dot.
This is a pretty minimalistic example of a particle engine but the basics are there. You can make more advanced and better looking particles by making more detailed animations, adding properties like velocity, acceleration, and rotation, or even have the particles interact with each other.

Experiment and see what effects you can create.
Download the media and source code for this tutorial here.

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