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Spawner tutorial


This tutorial is showing how to use spawners.
NB: If you want to see how to use orx while using C++ for your game, please refer to the localization tutorial.

See previous basic tutorials for more info about basic object creation, clock handling, frames hierarchy, animations, cameras & viewports, sounds & musics, FXs, physics, scrolling and C++ localization.

This tutorial shows how to create and use spawners for particle effects.
It's only a tiny possibility of what can be achieved using them.
For example, they can be also used for generating monsters or firing bullets, etc…

The code here is only used for two tasks:

  • creating 1 main object (a scene) and a viewport
  • switching from one test to another one by reloading the appropriate config files

Beside that, this tutorial is completely data-driven: the different test settings and the input definitions are stored in the config files along all the spawning/move/display logic.

With this very small amount of lines of code, you can have an infinite number of results: playing with physics, additive/multiply blend, masking, speed/acceleration of objects, etc…
It's all up to you! All you need is changing the config files and you can even test your changes without restarting this tutorial: config files will be entirely reloaded when switching from a test to another.

If there are too many particles displayed for your config, just turn down the amount of particles spawned per wave and/or the frequency of the waves.
To do so, search for the WaveSize/WaveDelay attributes in the different spawner sections. Have fun! =)


Let's begin with a quick look to our main function.

int main(int argc, char **argv)
  orx_Execute(argc, argv, Init, Run, Exit);
  return EXIT_SUCCESS;

Nothing new here, we only execute orx using the helper orx_Execute function, providing three callbacks: Init(), Run() and Exit().

Let's now have a glimpse to our Init() function.

  return LoadConfig();

We simply call our LoadConfig() function that will be described below.

void orxFASTCALL Exit()

As you can see, our Exit() function is even shorter as we will let orx the task of cleaning everything when we quit. =)

  orxSTATUS eResult = orxSTATUS_SUCCESS;
  if(orxInput_IsActive("NextConfig") && orxInput_HasNewStatus("NextConfig"))
    ss32ConfigID = (ss32ConfigID < orxConfig_GetListCounter("ConfigIDList") - 1) ? ss32ConfigID + 1 : 0;
  else if(orxInput_IsActive("PreviousConfig") && orxInput_HasNewStatus("PreviousConfig"))
    ss32ConfigID = (ss32ConfigID > 0) ? ss32ConfigID - 1 : orxConfig_GetListCounter("ConfigIDList") - 1;
  else if(orxInput_IsActive("Quit"))
    eResult = orxSTATUS_FAILURE;
  return eResult;

In our Run() function, in addition to quitting when the input Quit is active, we update our global ss32ConfigID which is an index to our currently selected config, depending on our inputs PreviousConfig & NextConfig status.
They'll then both call LoadConfig() that will reload everything.

Let's now have a closer look to LoadConfig().

static orxINLINE orxSTATUS LoadConfig()
  orxSTATUS eResult = orxSTATUS_FAILURE;
    pstScene = orxNULL;
    pstViewport = orxNULL;
  if(ss32ConfigID < orxConfig_GetListCounter("ConfigList"))
    orxSTRING zConfigFile;
    zConfigFile = orxConfig_GetListString("ConfigList", ss32ConfigID);
    if((eResult = orxConfig_Load(zConfigFile)) != orxSTATUS_FAILURE)
      pstViewport = orxViewport_CreateFromConfig("Viewport");
      pstScene = orxObject_CreateFromConfig("Scene");
  return eResult;

As you can see we first delete our Viewport and our Scene object, if needed.
We then clean the whole config content and reload our main config file 1).
We then try to find the current config settings we want from the ConfigList.
If we've found it, we then load the corresponding file.
Some config files will add new properties, some will override basic ones (like the Viewport background color or the content of the Scene object).
Finally we (re-)create our Viewport and our Scene object.

And we're done for the code! =D

Again, nothing really specific here to spawners or particle handling: all the magic will come from the config files. ;-)

In the same way we did for the C++ localization tutorial, the config file in our subfolder 2) merely includes the config file from the parent folder.
We'll then skip this one and directly have a look to the parent folder's one.

As you can see by looking at the config file, we provide values for all basics system (Display, Physics, Input, Viewport, etc…).
As we've already covered all this in previous tutorials, we won't do it here again.

However, there's an additional section called Tutorial. Let's have a closer look.

ConfigList = ../11_Base.ini#../11_Blend.ini#../11_Mask.ini#../11_Physics.ini#../11_BlendMask.ini#../11_BlendPhysics.ini#../11_FusionFountain.ini#../11_MeltingDots.ini#../11_Shader.ini#../11_BlendShader.ini

If you remember, in our LoadConfig() function, we were selecting the Tutorial section 3) to look at the property called ConfigList.
This ConfigList provides our program with a list of config files, one file for each particle settings.
We then loaded the corresponding file manually by calling orxConfig_Load().

NB: All paths defined in config files are relative to the current directory at runtime. By default, it's the executable's one, hence the use of “../” in front of all our files.

Let's now look at some of them 4).

We begin with the most basic one: 11_Base.ini.

Name = Base

The first line tells orx to include ../11_ParticleBase.ini which will be instantly loaded and processed.
We then extend our Tutorial section by adding a property called Name that contains the value Base.
As we'll see later, we'll use this property to display on screen the current setting's name. =)

Let's see another one, such as 11_FusionFountain.ini.

Name = FusionFountain

As we can see, it's built the same way as 11_Base.ini, except that we now load 4 config files instead of a single one and that we provide a different name for Tutorial.Name.

NB: The file include order is important as the last included file might override properties defined in the first included one, which will happen in our case as we'll see later.

Let's now see 11_ParticleBase.ini which is included in all our settings.
We'll only cover the interesting details and skipp all the fx/particle configuration.

ChildList = ParticleSpawner

Now we know exactly the content of our Scene object! =)
Let's see what this ParticleSpawner is made of.

ChildList = Name
Spawner   = Spawner
Position  = (0, 200, 0)

Another child here! This one's called Name.
There's also an attribute called Spawner which is defined.

Let's have a very quick glance at the Name object.

Graphic   = NameGraphic
Position  = (0, 50, 0)
Pivot = Center
Text  = NameText
String = @Tutorial.Name

As we can see, Name is simply a text object, however it's content points to Tutorial.Name.
As we just saw, Tutorial.Name is different for each config setting.
This means that every time we create a ParticleSpawner object, we'll display the name of the current setting just next to it, thanks to the relative positioning in a parent/child relation. =)

Let's get back to our Spawner.

Object      = Particle
WaveSize    = 5
WaveDelay   = 0.01

Spawners can use far more attributes than the three defined above as we can see in, but those are the most important ones.

First, the Object attribute tells the spawner which kind of object it's going to spawn. In this case it's an object which is called Particle and that we won't describe here 5).

We can also learn from this spawner that it will spawn 5 of these Particle every 0.01 seconds by looking at the WaveSize and WaveDelay attributes.

So that's about it, our Spawner will spew 500 Particle every second as long as it's active.
Gladly the Particle object has a LifeTime attribute of 2.0 seconds which means we won't have more than 1000 Particle existing at the same time.

There are a lot of other attributes to have a better control over our Spawner, such as limiting the total number of object spawned, or the maximum number of existing objects at the same time, etc…

As we saw for the FusionFountain setting, we also load other config files.
Let's then have a look to them.
We'll begin with 11_ParticleBlend.ini

Texture = ../../data/object/particle2.png
Type        = color
StartValue  = (0, 0, 0) ~ (-50, -50, -50)
EndValue    = (-255, -255, -255)
Graphic   = ParticleGraphic
BlendMode = add
Color     = (255, 255, 0) # (0, 255, 0) # (255, 0, 255) # (0, 255, 255)
Position  = (-40, 0, 0) ~ (40, 0, 0)
WaveSize = 8
SlotList = FadeOut#Gravity

All those defined properties are actually overriding the ones defined in 11_ParticleBase.ini.

We can see that we want to spawn more Particle objects in every Spawner's wave 6).
We can also see that we change the Texture, the BlendMode and even the FX of our Particle, etc…

Let's now look at 11_ParticleMask.ini

ChildList = ParticleSpawner # Mask
Texture   = ../../data/object/mask.png
Pivot     = center
BlendMode = multiply
Graphic   = MaskGraphic
Position  = {0, 0, -0.1}
Color = (255, 255, 255)

The most important information we can see here is that our Scene object now has two children instead of one.
This means that, in addition to our ParticleSpawner object, we also create an object called Mask which will use a multiply BlendMode and will displayed on top of the spawned Particle objects 7).
We also change the color of our Particle so that it will always be white.

Finally, let's see 11_ParticleDot.ini.

First we can see that we change our Viewport background color.

BackgroundColor = (200, 200, 200)

As it's now a light grey, we also change the Name color to black.

Color = (0, 0, 0)

And we make sure we spawn only 5 Particle objects per wave.

WaveSize = 5

We also add a child to our Particle

ChildList = ParticleDot

That means that every Particle will have its own ParticleDot child that will follow it everywhere it goes! No more lonely Particle! :-D
Let's have a closer look to this ParticleDot.

Texture = ../../data/object/particle.png
Pivot   = center
Graphic   = ParticleDotGraphic
Position  = (0, 0, -0.001)
Alpha     = 1.0
Scale     = 0.9

We can see that this dot will be placed in front of each Particle 8) and that it will be a bit smaller than Particle as a relative scale of 0.9.
As they both use the same Texture, even if we scale Particle, ParticleDot will always have 0.9 times the size of its parent Particle.

That's it for particles, let's now have a quick look to 11_ParticleShader.ini.

ShaderList = Decompose

Here we add a shader called Colorize to our Viewport.

Code = "void main()
  float fRed, fGreen, fBlue;
  // Computes positions with offsets
  vec2 vRedPos    = vec2(gl_TexCoord[0].x + offset.x, gl_TexCoord[0].y + offset.y);
  vec2 vGreenPos  = vec2(gl_TexCoord[0].x, gl_TexCoord[0].y);
  vec2 vBluePos   = vec2(gl_TexCoord[0].x - offset.x, gl_TexCoord[0].y - offset.y);
  // Red pixel inside texture?
  if((vRedPos.x >= 0.0) && (vRedPos.x <= 1.0) && (vRedPos.y >= 0.0) && (vRedPos.y <= 1.0))
    // Gets its value
    fRed = texture2D(texture, vRedPos).r;
  // Green  pixel inside texture?
  if((vGreenPos.x >= 0.0) && (vGreenPos.x <= 1.0) && (vGreenPos.y >= 0.0) && (vGreenPos.y <= 1.0))
    // Gets its value
    fGreen = texture2D(texture, vGreenPos).g;
  // Blue pixel inside texture?
  if((vBluePos.x >= 0.0) && (vBluePos.x <= 1.0) && (vBluePos.y >= 0.0) && (vBluePos.y <= 1.0))
    // Gets its value
    fBlue = texture2D(texture, vBluePos).b;
  // Outputs the final decomposed pixel
  gl_FragColor = vec4(fRed, fGreen, fBlue, 1.0);
ParamList = texture#offset
offset    = (-0.05, -0.05, 0.0) ~ (0.05, 0.05, 0.0); <= Let's take some random offset

As you can see, we directly write our shader's code in the Code attribute.
In our case it's a trivial code that will decompose the color of a pixel into 3 channels and mix them with its neighbors.

After defining the code 9), we provide a parameter list called ParamList.
Here we define 2 parameters: texture and offset.
As you can see we give random values for the offset parameter. The random values will be picked when the shader Decompose is created.

We can also see that we didn't define our texture paremeter. This means its content will default to the current parent's texture: here it's our Viewport texture 10).

In our case all the parameters are code-independent, ie. they won't change at runtime.
However we can add runtime parameters that we can change on-the-fly, but this won't be covered in detail by this tutorial.

In order to do so, we need to add the attribute UseCustomParam with a value set to true.
If we do that, every time our shader will be executed, orx will send an orxEVENT_TYPE_SHADER event 11).
This event's payload will contain the parameter name 12), its type and its config default value.
You can then change its value on-the-fly to suit your needs.
There's a simple sine wave distortion example that you can see in the bounce demo which is included in orx's source package, source and config.


Source code: 11_Spawner.c

Config file: 11_Spawner.ini

1) so as to start on a fresh base that will be modified depending on which files will be loaded next
2) which also contains the executable
3) calling orxConfig_SelectSection()
4) they are all built the same way
5) it's mainly a graphical object with varying color, shape and physical properties that we use as a… particle! =)
6) the value previously defined was 5
7) the Particles are spawned with a default Z=0.0 whereas Mask has a Z=-0.1, which is closer to the camera
8) due to the relative Z=-0.001 positionning
9) which has to be a valid GLSL code
10) if the shader was attached on an object instead of on a viewport, texture will be the object's texture instead
11) with the eID == orxSHADER_EVENT_SET_PARAM
12) here it'd be texture or offset
tutorials/spawner.txt · Last modified: 2015/12/06 20:10 (16 months ago) (external edit)