A simple emitter

Description

Emitters can be created to deal with effects such as engine trails, weapons, smoke and much more. In this program a simple emitter is created that fires particles up into the air.

This example program relies on an external image named "test2.png":

Set up

The code that creates this emitter is as follows:

LoadImage ( 1, "test2.png" )


CreateParticles ( 1, 150, 250 )
SetParticlesImage ( 1, 1 )
SetParticlesStartZone ( 1, -5, 0, 5, 0 )
SetParticlesDirection ( 1, 0, -145 )
SetParticlesAngle ( 1, 15 )
SetParticlesFrequency ( 1, 60 )
SetParticlesLife ( 1, 1.5 )
SetParticlesSize ( 1, 16 )
AddParticlesColorKeyFrame ( 1, 0, 255, 255, 255, 255 )
AddParticlesColorKeyFrame ( 1, 1.5, 255, 255, 255, 0 )

agk::LoadImage ( 1, "test2.png" );


agk::CreateParticles ( 1, 150, 250 );
agk::SetParticlesImage ( 1, 1 );
agk::SetParticlesStartZone ( 1, -5, 0, 5, 0 );
agk::SetParticlesDirection ( 1, 0, -145.0f );
agk::SetParticlesAngle ( 1, 15 );
agk::SetParticlesFrequency ( 1, 60 );
agk::SetParticlesLife ( 1, 1.5 );
agk::SetParticlesSize ( 1, 16 );
agk::AddParticlesColorKeyFrame ( 1, 0, 255, 255, 255, 255 );
agk::AddParticlesColorKeyFrame ( 1, 1.5, 255, 255, 255, 0 );

Understanding the code

The code performs the following actions:

loads the image "test2.png" into slot 1
creates particles with an ID of 1 positioned at 150, 250
applies image 1 ("test2.png") to the particles
alters the start zone for particles on the X axis by -5 and +5
applies a negative value on the Y direction forcing all particles to be emitted so they move up the screen
sets the angle of emission between 0 and 15 allowing a little variation on the Y axis
sets the frequency to 60 particles per second
reduces the life span of particles to 1.5 seconds
changes the size of particles to be 16 pixels
adds one color key frame that is used at the beginning of the particle's life - with full alpha
adds one color key frame that is used at the end of the particle's life - with no alpha thus forcing the particle to fade out

Main Loop

Our main loop simply needs to make a call to Sync to update the screen:

do
    Sync ( )
loop

void app::Loop ( void )
{
    agk::Sync ( );
}

Full code listing

Everything is now in place. Here's the final code for our program:

SetVirtualResolution ( 320, 480 )


CreateSprite ( LoadImage ( "alien_backdrop.jpg" ) )


LoadImage ( 1, "test2.png" )


CreateParticles ( 1, 150, 250 )
SetParticlesImage ( 1, 1 )
SetParticlesStartZone ( 1, -5, 0, 5, 0 )
SetParticlesDirection ( 1, 0, -145 )
SetParticlesAngle ( 1, 15 )
SetParticlesFrequency ( 1, 60 )
SetParticlesLife ( 1, 1.5 )
SetParticlesSize ( 1, 16 )
AddParticlesColorKeyFrame ( 1, 0, 255, 255, 255, 255 )
AddParticlesColorKeyFrame ( 1, 1.5, 255, 255, 255, 0 )


do
    Sync ( )
loop

void app::Begin ( void )
{
agk::SetVirtualResolution ( 320, 480 );


agk::CreateSprite ( agk::LoadImage ( "alien_backdrop.jpg" ) );


agk::LoadImage ( 1, "test2.png" );


agk::CreateParticles ( 1, 150, 250 );
agk::SetParticlesImage ( 1, 1 );
agk::SetParticlesStartZone ( 1, -5, 0, 5, 0 );
agk::SetParticlesDirection ( 1, 0, -145.0f );
agk::SetParticlesAngle ( 1, 15 );
agk::SetParticlesFrequency ( 1, 60 );
agk::SetParticlesLife ( 1, 1.5 );
agk::SetParticlesSize ( 1, 16 );
agk::AddParticlesColorKeyFrame ( 1, 0, 255, 255, 255, 255 );
agk::AddParticlesColorKeyFrame ( 1, 1.5, 255, 255, 255, 0 );
}


void app::Loop ( void )
{
    agk::Sync ( );
}

Conclusion

With a few lines of code a fairly complex emitter has been generated. This could be used for all kinds of effects such as the exhaust from an engine, poisonous gas escaping from a pipe, smoke and much more.