Lazy Foo' Productions

Particle Engines

Last Updated 5/04/14
Particles are just mini-animations. What we're going to do is take these animations:
and spawn them around a dot to create a trail of colored shimmering particles.
//Particle count const int TOTAL_PARTICLES = 20; class Particle { public: //Initialize position and animation Particle( int x, int y ); //Shows the particle void render(); //Checks if particle is dead bool isDead(); private: //Offsets int mPosX, mPosY; //Current frame of animation int mFrame; //Type of particle LTexture *mTexture; };
Here is a simple particle class. We have a constructor to set the position, a function to render it, and a function to tell if the particle is dead. In terms of data members we have a position, a frame of animation, and a texture we'll render with.
//The dot that will move around on the screen class Dot { public: //The dimensions of the dot static const int DOT_WIDTH = 20; static const int DOT_HEIGHT = 20; //Maximum axis velocity of the dot static const int DOT_VEL = 10; //Initializes the variables and allocates particles Dot(); //Deallocates particles ~Dot(); //Takes key presses and adjusts the dot's velocity void handleEvent( SDL_Event& e ); //Moves the dot void move(); //Shows the dot on the screen void render(); private: //The particles Particle* particles[ TOTAL_PARTICLES ]; //Shows the particles void renderParticles(); //The X and Y offsets of the dot int mPosX, mPosY; //The velocity of the dot int mVelX, mVelY; };
Here is our dot with an array of particles and a function to render the particles on the dot.
Particle::Particle( int x, int y ) { //Set offsets mPosX = x - 5 + ( rand() % 25 ); mPosY = y - 5 + ( rand() % 25 ); //Initialize animation mFrame = rand() % 5; //Set type switch( rand() % 3 ) { case 0: mTexture = &gRedTexture; break; case 1: mTexture = &gGreenTexture; break; case 2: mTexture = &gBlueTexture; break; } }
For our particle constructor we initialize the position around the given position with some randomness to it. We then initialize the frame of animation with some randomness so the particles will have varying life. Finally we pick the type of texture we'll use for the particle also at random.
void Particle::render() { //Show image mTexture->render( mPosX, mPosY ); //Show shimmer if( mFrame % 2 == 0 ) { gShimmerTexture.render( mPosX, mPosY ); } //Animate mFrame++; }
In the rendering function we render our texture selected in the constructor and then every other frame we render a semitransparent shimmer texture over it to make it look like the particle is shining. We then update the frame of animation.
bool Particle::isDead() { return mFrame > 10; }
Once the particle has rendered for a max of 10 frames, we mark it as dead.
Dot::Dot() { //Initialize the offsets mPosX = 0; mPosY = 0; //Initialize the velocity mVelX = 0; mVelY = 0; //Initialize particles for( int i = 0; i < TOTAL_PARTICLES; ++i ) { particles[ i ] = new Particle( mPosX, mPosY ); } } Dot::~Dot() { //Delete particles for( int i = 0; i < TOTAL_PARTICLES; ++i ) { delete particles[ i ]; } }
The constructor/destructor now have to allocate/deallocate the particles we render over the dot.
void Dot::render() { //Show the dot gDotTexture.render( mPosX, mPosY ); //Show particles on top of dot renderParticles(); } void Dot::renderParticles() { //Go through particles for( int i = 0; i < TOTAL_PARTICLES; ++i ) { //Delete and replace dead particles if( particles[ i ]->isDead() ) { delete particles[ i ]; particles[ i ] = new Particle( mPosX, mPosY ); } } //Show particles for( int i = 0; i < TOTAL_PARTICLES; ++i ) { particles[ i ]->render(); } }
Our dot's rendering function now calls our particle rendering function. The particle rendering function checks if there are any particles that are dead and replaces them. After the dead particles are replaced we render all the current particles to the screen.
bool loadMedia() { //Loading success flag bool success = true; //Load dot texture if( !gDotTexture.loadFromFile( "38_particle_engines/dot.bmp" ) ) { printf( "Failed to load dot texture!\n" ); success = false; } //Load red texture if( !gRedTexture.loadFromFile( "38_particle_engines/red.bmp" ) ) { printf( "Failed to load red texture!\n" ); success = false; } //Load green texture if( !gGreenTexture.loadFromFile( "38_particle_engines/green.bmp" ) ) { printf( "Failed to load green texture!\n" ); success = false; } //Load blue texture if( !gBlueTexture.loadFromFile( "38_particle_engines/blue.bmp" ) ) { printf( "Failed to load blue texture!\n" ); success = false; } //Load shimmer texture if( !gShimmerTexture.loadFromFile( "38_particle_engines/shimmer.bmp" ) ) { printf( "Failed to load shimmer texture!\n" ); success = false; } //Set texture transparency gRedTexture.setAlpha( 192 ); gGreenTexture.setAlpha( 192 ); gBlueTexture.setAlpha( 192 ); gShimmerTexture.setAlpha( 192 ); return success; }
To give our particles a semi transparent look we set their alpha to 192.
//Main loop flag bool quit = false; //Event handler SDL_Event e; //The dot that will be moving around on the screen Dot dot; //While application is running while( !quit ) { //Handle events on queue while( SDL_PollEvent( &e ) != 0 ) { //User requests quit if( e.type == SDL_QUIT ) { quit = true; } //Handle input for the dot dot.handleEvent( e ); } //Move the dot dot.move(); //Clear screen SDL_SetRenderDrawColor( gRenderer, 0xFF, 0xFF, 0xFF, 0xFF ); SDL_RenderClear( gRenderer ); //Render objects dot.render(); //Update screen SDL_RenderPresent( gRenderer ); }
Again, since our code is well encapsulated the code in the main loop hardly changes.

Now like most of the tutorials this is a super simplified example. In larger program there would be particles controlled by a particle emitter that's its own class, but for the sake of simplicity we're having the Dot class function as a particle emitter.
Download the media and source code for this tutorial here.

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