Mastering the GameMaker Studio Particle System

In this article, we’ll begin with the basics of the GameMaker Studio particle system and end with advanced techniques and implementations. Think of this as a crash course to get you familiar and comfortable with one of GameMaker Studio’s most powerful built-in features. The demo and downloadable project file will allow you to follow along with the article to see exactly what the particle system is all about.

• How to Learn
  How to Learn GameMaker: Studio
  Jacob Ford

Particle System Overview

The GameMaker Studio particle system is a cheap and easy way to create flashy effects for your game project. Through a combination of particles and emitters, you can quickly create impressive explosions, smoke, blood, shrapnel, and countless other effects. Similar effects can be achieved by using individual objects, but the computing cost of the built-in particle effects system is far cheaper.

To use the particle system in your project, you'll need to understand GML (GameMaker Language), but once you become familiar with the particle system, it is simply a matter of filling in the blanks and experimentation.

Check out the demo below to see what we can achieve:

Particle System Basics

Particle Systems in GameMaker Studio consist of three parts: the system itself, the particle, and the emitter. You can create multiple systems, and each system can contain multiple particles and emitters. Think of the system as a container, with the particles and the emitters defined within.

Implementing a particle effect in GameMaker Studio is a four step process. 

1. First, you must define the particle system itself. 
2. Then, you define the actual particles that will be used within that system. 
3. Next, you have to define the emitter that will create your defined particles. 
4. Finally, you have to determine when and where the particle emitter will appear in your game.

To teach you the basics of the GameMaker Studio particle system, we’ll start out by creating this very simple green particle effect.

Creating the Particle System

Creating the particle system is as simple as defining a variable. We create an object called obj_first_particle and place the following code in the object’s Create event:

FirstParticleSystem = part_system_create();

The particle system will adopt the depth value of the object that the system is defined in, but you can also set the depth separately with GML:

part_system_depth(FirstParticleSystem,0);

Remember that objects and particle systems with a high depth value are drawn to the screen first. With a depth of 0, our green particle system will appear above objects with a depth greater than 0, and will appear below objects with a depth less than 0.

Particle systems are drawn to the screen with a base position relative to (0,0). If for some reason you want to create an offset for all future positions of this particle system, you can use the following code to create a new base position (where ind is the particle system):

part_system_position(ind, x, y);

With a new base position set to(10,10), a particle created at (25,25) will instead be drawn to (35,35). Changing the base position of a particle system is rarely necessary, but you may find it useful in your specific project.

Creating the Particle Type

Now that the system has been set up, it is time to define the actual particle that the emitter will create. Particles can contain a large number of parameters that dictate how the particle will look and behave. The first step is to create a variable for the particle, and we do this in the Create event of the obj_first_particle object:

first_particle = part_type_create();

Next, we begin defining the individual parameters of the particle. Since we do not plan on altering this particle during runtime, we can place all of this code in the Create event of the obj_first_particle object.

part_type_shape determines the base shape of the particle. There are 14 default particle shapes available in GameMaker Studio, and you can define your own shapes as well. We’ll cover this in the advanced section below, but for now let’s just start with a basic square.

part_type_shape(first_particle,pt_shape_square);

For a full list of the available default shapes, check the official GameMaker documentation.

With part_type_scale, we can set the base X and Y scale values of the particle shape. Since we want a perfect square shape, we use the following code:

part_type_scale(first_particle,1,1);

part_type_size allows us to alter the size of the particle at creation and as well as over time. The format for this code is part_type_size(ind, size_min, size_max, size_incr, size_wiggle). 

• ind is the particle variable. 
• size_min and size_max determine the range of the particle size when it is first created. If you want a uniform size, simply enter the same value for both the min and the max. 
• size_incr is a value that allows the particle to grow or shrink over time. This value determines the speed of growth, so if you don’t want your sprite to change size, you can use a value of 0. 
• size_wiggle is slightly more complicated, so we’ll cover that in the advanced techniques section below.

Here’s the particle size code used in our green particle effect:

part_type_size(first_particle,0.10,0.15,-.001,0);

The particle will be created with a size somewhere between 0.10 and 0.15 to create variety, and the sprite will slowly shrink at a speed of -0.001. This speed value depends greatly on your room speed, so you will likely need to experiment with values to get the desired results. We will not be using any size wiggle, so we set the value to0.

Particles in GameMaker Studio can actually change colors over time. This is achieved with part_type_color2 andpart_type_color3. If you don’t want your sprite to change colors, then you can just use part_type_color1. For our green particle effect, we want it to start out with a bright yellow/green color and then change to a solid green color, so we use part_type_color2:

part_type_color2(first_particle,8454143,65280);

The two colors I selected are specific numerical values that I use regularly, but if you want to use more traditional hex values, you can use the format $RRGGBB.

Particles can also become more or less transparent over time with part_type_alpha2 and part_type_alpha3. If you want a consistent alpha value, use part_type_alpha1. For our green particle effect, we want the particle to start completely opaque and fade by 25% as it stays on the screen, so we need two alpha values:

part_type_alpha2(first_particle,1,0.75);

In GameMaker, alpha is a value from 0 to 1. A completely invisible object will have an alpha value of 0, while a completely opaque object will have an alpha value of 1.

Particle speed is determined just like particle size. Particles are created within a range of speed values, and that value can increase or decrease. The format for this code is part_type_speed(ind, speed_min, speed_max, speed_incr, speed_wiggle), where ind is the particle variable, speed_min and speed_max is the speed range, speed_incr is the rate at which the particle speed changes, and speed_wiggle is a parameter that we’ll cover later on. 

The speed code for our green particle is:

part_type_speed(first_particle,0.1,0.5,0,0);

Our particle will start moving with a speed value somewhere between 0.1 and 0.5. This speed will remain constant, so we use a value of 0, and we will again not be implementing speed wiggle, so we use a value of 0.

While a particle’s speed parameter determines how fast it moves, the direction parameter determines where it moves. The direction code is in the following format: part_type_direction(ind, dir_min, dir_max, dir_incr, dir_wiggle) and again we set the variable, starting range, an incremental value, and a wiggle value. For the green particle effect, we want our particle to start moving in any direction, and we want that direction to remain constant:

part_type_direction(first_particle,0,359,0,0);

The range of 0 to 359 ensures that the particle has a chance to move in any direction (an angle between 0 and 359 degrees). If you wanted a particle to move up and only up, then you would use a range of 90 to 90).

The gravity of our particle effect is what makes it the most interesting. While our speed and direction parameters are set to create a particle that starts by moving in one direction at a constant speed, the gravity parameter kicks in and alters the particle over time. With a format of part_type_gravity(ind, grav_amount, grav_direction), the gravity parameter is very simple:

part_type_gravity(first_particle,0.02,90);

By applying a slight gravitational pull of 0.02 in an upward direction (90 degrees), we can create a particle that appears to float. Combined with our size and alpha parameters, the particle shrinks and becomes more transparent over time, accompanied by the gravitational lift.

The orientation of the particle shape is also important to the appearance of the effect, so we use part_type_orientation(ind, ang_min, ang_max, ang_incr, ang_wiggle, ang_relative) to rotate the square over time. 

• ind is the particle variable. 
• ang_min and ang_max determine the starting value of the shape’s rotation value.
• ang_incr is used to increment or decrement the shape’s orientation over time.
• ang_relative is a Boolean value to determine if the orientation should be set relative to the motion of the particle (true) or not (false). 

We want our green particle to rotate slightly to the left, so we use the following code:

part_type_orientation(first_particle,0,359,10,0,true);

One of the most important parameters of a particle is the lifespan value. This value determines the minimum and maximum time that a particle will be drawn to the screen. With two identical min and max values, all particles of that type will exist for the same amount of time. We want our green particles to have variety, so we will use a range of 100 to 150 for the lifespan value:

part_type_life(first_particle,100,150);

The final parameter for particles is a simple Boolean to determine whether the particles should blend together with an additive blend effect:

part_type_blend(first_particle,true);

Creating the Particle Emitter

The first step in defining an emitter is to create a variable. We define this emitter in the Create event of the obj_first_particle object.

first_emitter = part_emitter_create(FirstParticleSystem);

Next, we define the emitter region with part_emitter_region(ps, ind, xmin, xmax, ymin, ymax, shape, distribution).

• ps is the particle system that the emitter belongs to and ind is the emitter variable.
• The x and y min and max values determine the size of the emitter region. 
• shape determines the shape of the emitter region (ps_shape_rectangle, ps_shape_ellipse, ps_shape_diamond, ps_shap_line). 
• distribution is a distribution curve (ps_dist_linear, ps_distr_gaussian, ps_distr_invgaussian).

We’ll cover the shape and distribution parameters in further detail in the advanced techniques section. For now, we’ll use the default ellipse shape and Gaussian distribution values:

part_emitter_region(FirstParticleSystem, first_emitter, x-20, x+20, y-20, y+20, ps_shape_ellipse, ps_distr_gaussian);

This code creates an elliptical emitter region that is 40 pixels tall and 40 pixels wide, and centred on the x and y values of the obj_first_particle object. Particles created by the emitter will appear within this defined region.

Activating the Particle Emitter

The next step is to determine one of two emitter types: Burst or Stream. A Burst emitter creates a specified amount of a certain particle whenever it is triggered. A Stream emitter creates a specified amount of a certain particle once every step. 

We’ll take a look at the more versatile Burst emitters in the advanced techniques section, so for now let’s just use the Stream emitter:

part_emitter_stream(FirstParticleSystem,first_emitter,first_particle,1);

We place this code in the Create event of the obj_first_particle object, resulting in the emitter creating one particle each step as soon as the object is created. With a room speed of 30, our emitter will create 30 particles per second; to create 60 particles per second, you would simply use a value of 2 instead of 1.

And with that, our simple green particle effect is complete! The usefulness of this effect is limited, but it’s important to start small before diving into the more complicated aspects of the GameMaker Studio particle system. Once you understand the basics of the particle system, you can start implementing more advanced particle systems.

Advanced Particle System Techniques

Particle Wiggle

Wiggle is a simple, yet powerful parameter that can drastically change the appearance of your particles. The wiggle parameter causes the particle to oscillate between the min and max values for the lifetime of the particle. The value can be between 0 and 20 and determines the speed of the wiggle. 

The "Fire Bubble" example in the embedded demo uses a wiggle value of 0.40 in the part_type_size parameter:

part_type_size(fire_bubble_part,0.25,0.75,-0.01,0.40);

Burst Emitters and Moving Objects

One of the most common implementations of particle systems involves particles that emanate from behind a moving object, such as a smoke trail on a rocket. Achieving this effect in GameMaker Studio requires a Burst emitter to be placed in an object’s Step event.

The included example uses the same green particle system as before, but with a slightly modified emitter. Instead of triggering a Stream emitter in the object’s Create event, a Burst emitter is placed in the object’s Step event. The current position of the mouse cursor is checked against the previous position of the cursor, and if there is a change in the cursor’s position, the Burst emitter is triggered to release five particles:

x = mouse_x;
y = mouse_y;

part_emitter_region(MouseParticle,green_mouse_emitter,x,x,y,y,0,0);

if x != old_x || old_y != y
{
    part_emitter_burst(MouseParticle,green_mouse_emitter,green_mouse_particle,5);
}

old_x = x;
old_y = y;

Emitter Region Shapes

By using the different emitter shapes and distribution curves, you can create vastly different effects. Linear curve distribution combined with a line-shaped particle emitter can create a convincing rain effect.

part_emitter_region(RainParticle, rain_emitter, -100, room_width, y, y, ps_shape_line, ps_distr_linear);

The emitter shape is defined by a line that begins 100 pixels to the left of the room origin and is extended to the width of the room. A linear distribution curve is used to distribute the rain particles evenly across the emitter region. It is also useful to usepart_system_update to advance the rain particle several steps in the Create event. This code gives the impression that the rain was falling before you loaded the room, even though the particle system didn’t exist in memory yet.

repeat (room_speed * 3)
{
     part_system_update(RainParticle);
}

Particle System Step and Death Effects

Individual particles within a system can also spawn other particles on Step and Death events. The example shows a purple spark particle that spawns smaller dust particles as it travels to the right, and spawns a smoke particle at the end of its lifespan:

part_type_step(spark_particle,1,dust_particle);
part_type_death(spark_particle,5,smoke_particle);

Custom Particle Shapes

By using part_type_sprite(ind, sprite, animate, stretch, random), you can use custom sprites instead of the built-in GameMaker particle types. 

• ind is the particle variable.
• sprite is the sprite variable to be used.
• animate is a Boolean to determine if the sub-images should be animated.
• stretch is a Boolean that matches the animation length to the lifespan of the particle. 
• random is a Boolean to determine whether the starting sub-image should be randomly selected.

part_type_sprite(heart_particle,spr_heart,false,false,false);

Memory Management

The most important thing to remember about the GameMaker Studio particle system is that you need to manually remove items from memory when not in use. Unlike standard game objects, particle systems will remain in memory even if you change rooms. The easiest way to handle this is to place memory management code in the room changing events of your game objects.

• part_system_clear(ind): Clears all emitters and particles belonging to a specific particle system.
• part_system_clear(ind): Clears all instances of a specific particle type.
• part_emitter_clear(ps, ind): Clears all particles belonging to a specific emitter.
• part_emitter_destroy(ps, ind): Destroys a specific emitter in a specific particle system.
• part_emitter_destroy_all(ps): Destroys all emitters in a specific particle system.
• part_type_destroy(ind): Destroys a specific particle type.
• part_system_destroy(ind): Destroys an entire particle system, including all particles and emitters contained within.

Conclusion

Even with such a lengthy tutorial, we've still only scratched the surface of what kinds of effects the GameMaker Studio particle system is capable of. The key to mastering particles is familiarity and experimentation, so jump in and start creating your own effects using the knowledge you've gained. Be sure to check out the official GameMaker documentation to view all the available particle system GML!